Nos équipes de recherche - Quantum

Equipes de recherche

• EPLA

Activités de recherche

Superconducting Silicon resonators

To propose superconducting silicon as a serious candidate for quantum engineering, a fundamental study of its high frequency properties is necessary. We have fully characterized the first coplanar waveguide superconducting silicon resonators. Multiple resonators are coupled to the same transmission line, allowing frequency-domain multiplexing. The resonators show well-controlled resonant frequency in the 1-10 GHz range, with a Q-factor of the order of 4000 (limited by magnetic vortices and to improve), and a well-understood BCS dependence with temperature. The resonators have large kinetic inductances ~ 500 pH/sq and a strong non-linearity with power to explain. The quasiparticles show ms-recombination times without particular shielding, optimal for increased responsivity in photon detectors.

CMOS-compatible, scalable and integrable Si Josephson transistors

Obtained by out-of-equilibrium laser doping, superconducting silicon layers with sub-K critical temperatures can be epitaxied over a Si substrate. The epitaxial sharp laser doping profile is associated with a doped Si/Si highly transparent, ohmic interface (an order of magnitude less resistive than that of metallic superconductor/Si interfaces). We have thus been able to induce a long-range proximity effect in a non-superconducting silicon wire, demonstrating a nondissipative supercurrent through all-silicon Josephson junctions. Our aim is now to demonstrate that this supercurrent can be modulated by an electrostatic gate in the low-doped silicon channel, realizing a Josephson transistor (JoFET). In parallel, we collaborate with LETI and CEA to reproduce such results on FD-SOI CMOS.

Electroluminescence of ultra-doped Si LEDs

In weakly spin–orbit coupled materials, such as Si, the spin-selective nature of recombination can give rise to large magnetic-field effects. However, observing spin-dependent recombination through magneto-electroluminescence (M-EL) is challenging: Si indirect bandgap causes an inefficient emission and it is difficult to separate spin-dependent phenomena from classical magneto-resistance (MR). We have overcome these challenges and measured M-EL in silicon LED fabricated via laser doping. These devices allow us to achieve efficient emission while retaining a well-defined geometry, suppressing classical MR to a few percent. EL could be enhanced up to 300% near room temperature in a 7 Tesla field, showing that the control of the spin degree of freedom can have a strong impact on the efficiency of silicon LEDs.

• PHENIX

Activités de recherche

Croissance par MOCVD d’hétérostructures semiconductrices sur InP, GaAs et GaP pour

1. la nanophotonique télécom et MIR,
2. le contrôle de la lumière émise de VECSEL (bruit quantique d’intensité ou de phase, cohérence du laser, bifréquence pour horloge atomique au Cs, injection de spin),
3. l’amplification paramétrique optique ou la génération de différence de fréquence dans le proche IR à base de domaines d’orientation alternés en GaP,
4. le traitement analogique des signaux à l’aide d’oscillateurs optomécaniques à base de GaAs et GaP, 5) l’émission de photons unique aux longueurs d’onde télécom à base de boites quantiques localisées sur InP.

• Physique Quantique dans les Circuits

Activités de recherche

L’équipe Physique Quantique dans les Circuits explore un large spectre de physique fondamentale dans les circuits électriques, de la matière électronique corrélée au transport quantique, jusqu’au niveau le plus élémentaire de l’unique canal de conduction. Principales lignes de recherche en cours : – Physique à N corps dans les circuits quantiques : liquides de Luttinger, effet Kondo, transitions de phase quantiques. – Transport quantique de la chaleur et transferts d’énergie dans les circuits mésoscopiques.

• 2DEG Haute mobilité pour les dispositifs quantiques

Activités de recherche

High-mobility 2DEGs

Cryo HEMT

This research activity is centred around the epitaxial growth of GaAs-based twodimensional electron gases (2DEGs) for the study of electronic transport properties. In these 2DEGs the electron mean free path at low temperatures can be several tenths of micrometers, and the quantum phase can be preserved for up to a quarter of a mm. They are therefore the supreme ‘work horse’ for mesoscopic physics, where we try to understand the convergence between electronic transport and quantum mechanical properties. Within this activity, we also develop the fabrication of nano-devices for mesoscopic physics using our 2DEG material. One such development has been of a ‘meso-collider’ for the study of anyonic statistics, in a collaboration LPENS.

We develop specific process for various fieldeffect devices including a new generation of ultra-low noise cryoHEMTs for low frequency high impedance deep cryogenic readout electronics. Low-temperature readout electronics is essential to suppress various unwanted effects due to the long cable between the measured signal at low temperature and the room-temperature readout electronics: the triboelectric effect, microphonic noise, capacitive coupling noise and data-acquisition rate slow-down. Based on a long-term investigation of material growth and device process, the cryoHEMTs (Cryogenic High Electrons Mobility Transistors) made at the C2N (formerly LPN) are now in the process to fill the gap of the FET (Filed-Effet Transistor) for high impedance, low-power and lowfrequency deep cryogenic readout electronics. Different input capacitance cryoHEMTs have been fabricated and characterized, and ultralow noise voltage and, in particular, unprecedented low noise current have been obtained.

• Topological states in 2D materials (Topo2D)

Activités de recherche

We investigate topologically protected states affecting the valley and spin degree of freedom of 2D materials. These states are robust to arbitrary perturbations and can be used in future quantum technologies. To investigate these states, we combine innovative sample fabrication techniques, angular layer alignment of 2D materials and low temperature electron transport.

• C2N/ Microscopie et spectroscopie tunnel

Activités de recherche

 Surface de GaAs (110) vue par STM, montrant les orbitales de dopants de manganèse.

Les travaux de l’équipe portent sur l’étude des propriétés électroniques de surface sondées à l’échelle atomique grâce aux techniques de microscopie et spectroscopie à effet tunnel (STM/STS) appliquées aux semi-conducteurs (III-V, II-VI, dichalcogénures, matériaux 2D), et isolants (oxydes, isolants topologiques), possédant tous des propriétés quantiques remarquables. Notre équipe travaille sur des impuretés et défauts atomiques individuels magnétiques dans ces matériaux. Le STM est un outil unique pour construire des systèmes à l’échelle de l’atome grâce à la manipulation atomique par la pointe. Enfin, nous développons la technique de résonance paramagnétique électronique par STM (ESR-STM) qui apporte la résolution spatiale et permet de réduire les mesures de résonance paramagnétique à un spin unique.

• Quantum dots and photonic nanostructures (C2N/PHOTONICS/QD)

Activités de recherche

Planar Nanotechnology for quantum information

GaN optical waveguide coupled to a GaN quantum well microdisk cavity with a 45 nm air gap. 

Silicon and diamond and III-N nitride nanotechnology, partly in the context of quantum information processing integration on planar platforms. Starting projects: Nonlinear optical parametric processes for quantum technologies. Simulation of quantum mesoscopic wave systems using optical nanoresonators. Interaction of free single electrons with single photons confined into a microscopic optical cavity. Non-local semiquantum effects in plasmonic doped nanocrystals.

k.p Schrödinger equation

14-band k.p electronic structure of HgSe in pressure and temperature 

Modelling of the electronic structure of semiconductor colloidal nanocrystals using multiband k.p Schrödinger equation solving.

Semi-classical plasmonic modelling

Absorption spectra of an ensemble of disordered semiconductor plasmonics nanocrystals with various quantics confinement intensity (β/β0) of the electron gaz.

Modelling of semiconductor plasmonics nanocrystals with a semi-classical Hydrodynamic Drude model.

• ODIN

Activités de recherche

Quantum functionalities enabled by strong light-matter coupling 

Integrated polariton micro-lasers – a path towards lowthreshold, low-energy per bit, compact coherent light sources

• Transport électronique assisté par photons virtuels dans les systèmes électroniques 2DEG en couplage fort lumière-matière
• Optique non-linéaire avec petit nombre de photons dans la gamme spectrale du moyen-infrarouge
• Emission de photons corrélés stokesanti- stokes en régime de couplage-fort vibrationnel

• Integrated polariton lasers at room temperature using wide bandgap materials
• Electrical injection of polaritons for waveguided polaritonic circuits

• ToniQ : nanophoTOnique non-linéaire et Information Quantique

Activités de recherche

Sources d’intrication multipartite aux longueurs d’onde télécom

Schéma de générateur versatile d’intrication multipartite avec des guides non-linéaires couplés 

L’intrication multipartite est une ressource centrale pour l’avenir de l’information quantique. Notre objectif est la démonstration de sources quantiques avancées, intégrées, opérant aux longueurs d’onde télécom et T ambiante et leur utilisation dans des protocoles d’IQ. Ces sources utilisent des interactions optiques non-linéaires. En X(2), nous considérons des guides/réseaux de guides en LiNbO3. Le couplage entre guides et la nonlinéarité produisent des états intriqués versatiles et distribuables, ce qui différentie l’approche d’autres intrications multipartites. En X(3), nous étudions d’une part la génération directe d’états triplets de photons dans des guides de KTP. D’autre part, nous développons des peignes de fréquence par mélange à 4 ondes dans deux plateformes compatibles SOI : micro-résonateurs en Si et nano-résonateurs à cristaux photoniques hybrides III-V/Si. Nous visons notamment la manipulation de bins fréquentiels.

Transitions de phase dissipatives et intrication 

Cavités non-linéaires couplées avec contrôle du couplage et de la nonlinéarité 

Le lien en optique entre dynamique non-linéaire et réponse quantique a été étudié dès les années 80 notamment dans les cas d’un résonateur bistable et est désormais bien compris. Ceci n’est pas le cas pour la dynamique à N-corps hors d’équilibre et en régime dissipatif, où ce lien entre le squelette des bifurcations classiques et le comportement quantique n’est exploré que depuis peu. Nous avons développé une plateforme à cristal photonique en semiconducteur III-V où le couplage entre nanocavités et la réponse nonlinéaire peuvent être ajustés par design. Pour des faibles nombres de photons nous avons démontré : la brisure spontanée de symétrie, des cycles limites et de l’émission superthermique. Cette plateforme constitue un outil de choix pour explorer l’interface entre la dynamique non-linéaire et l’optique quantique dans des réseaux de nanocavités couplées.

Couplage fort hybride pour l’information et la métrologie quantiques 

Membrane suspendue à cristal photonique pour le couplage opto-mécanique

Coupler/intriquer des systèmes appartenant à deux « mondes » différents est un objectif majeur pour des nombreuses applications quantiques, mais est technologiquement compliqué. 

Dans le cadre du projet FET-OPEN DAALI nous développons une plateforme à cristal photonique en GaInP transparente aux longueurs d’ondes de résonance des atomes d’un nuage froid de Rb et permettant le couplage fort entre le mode nanophotonique et chaque atome individuel. Ainsi des applications en IQ sont envisagées mettant en jeu le contrôle de l’état d’un seul atome pour faire basculer le comportement collectif. La mesure de la température thermodynamique a largement profité des avancées récentes dans la détermination de la constante de Boltzman. Cependant, les systèmes les plus performants restent encombrants et fragiles. Dans le cadre du projet EUROMET PhotOQuant nous développons une approche originale basée sur le couplage optomécanique dans une plateforme à cristal photonique dans laquelle la contre réaction de la pression de radiation permettra d’intriquer les résonnances optique et mécanique pour atteindre une sensibilité quantique.

• EXPERFO

Activités de recherche

Experimental demonstrators and functional device characterization for high speed digital communications over optical fiber

• C2N/PQF Polariton Quantum Fluids at C2N

Activités de recherche

Fluids of light

Emission of a 1D cavity showing an extended polariton condensate and optically trapped polaritons.

We study the physics of fluids of light in semiconductor microcavities, with the aim of developing new photonic devices and also exploring the non-linear dynamics of dissipative systems. The optical excitations of these cavities (called "exciton polaritons") behave like fluids of light with fascinating physical properties. Due to their photonic nature, they propagate like light, they can be confined in structures of micrometer size. Polaritons also feature optical non-linearities (Kerr-type) which gives them fascinating properties such as superfluidity, vortex nucleation, or Bose Einstein condensation when all polaritons massively occupy massively the same state. We are interested in the generation of these condensates, their manipulation in microstructures, and their properties of coherence and stability.

Topology in arrays of polariton microcavities

Electron microscopy image of a 1D array of micro-pillars with an artistic representation of the laser emission in a topological state.

Our group has developed state-of-the-art technology to manufacture optical microcavity lattices with well-chosen band structures and topological properties. For example, we studied networks of photonic graphene, and observed their edge states as well as other phenomena emerging from the topological properties of Dirac cones. Taking advantage of the non-linear properties of polaritons, we recently demonstrated topological lasing in a 1D array, where the laser mode is protected from perturbations in its environment due the system's topology. Finally, we are interested in the topological phases of quasi-crystals, which have fractal band structures and allow us to imitate the quantum hall effect.

Quantum optics in polariton lattices

A schematic image of a polariton lattice. In the strongly interacting regime, light escaping from the array shows quantum properties.

One of our research activities is to study the quantum properties of the photonic lattices we develop in the group. Indeed, in the strong coupling regime between light and between the electronic excitations of the system, we generate hybrid light-matter quasi-particles, which behave like interacting photons. Nowadays, the major challenge for photonic platforms is to generate sufficiently strong interactions between polaritons, to generate quantum correlations between photons escaping from these synthetic structures. Our goal is to investigate the optical signatures of this quantum behavior, as a function of the dimensionality of the system (1D or 2D) and of the topology of its band structure.

• C2N/OMN OptoMechanics and Nanophononics

Activités de recherche

Ultrahigh frequency nanophononics

SEM image of an opto-phononic micropillar resonator

The study of mechanical systems in their quantum ground state motivates the development of novel mechanical resonators with frequencies higher than a few GHz. In this particular frequency range, standard cryogenic techniques become sufficient to reach the quantum regime without relying on additional sideband optical cooling. Recently, we presented GaAs/AlAs pillar microcavities as new optomechanical resonators performing in the unprecedented 18-100 GHz mechanical frequency range, showing highly promising features such as state-of-the-art quality factorfrequency products. We explore novel phonon confinement strategies as well as innovative measuring techniques, and the coupling with quantum emitters.

Localization phenomena, transport, and topological nanoacoustics

(top) Schematics of the Raman scattering measurement in a topological phononic sample. (bottom) Raman spectra of a topologically confined acoustic mode.

Acoustic transport, integration, and topological phenomena Acoustic waves represent a versatile platform for the study of wave dynamics and localized excitations. More generally, acoustic waves spanning the MHz-THz range can be used for the study of the information exchange between different (quantum and classical) optomechanical platforms working in completely different mechanical and/or optical frequencies. The C2N has the leverage to tackle the engineering of efficient resonators and waveguides, and the integration and the coupling of multiple oscillators. Topological phenomena, Anderson co-localization of acoustic phonons and visible photons, synchronization, chaos, and transport are a few examples of the physics explored in this research line.

Quantum electroopto nanomechanics

SEM image of an electro-optomechanical crystal.

Optomechanics with photonic crystals has evidence the strong colocalization of optical and mechanical modes in the GHz range. Such emblematic structure of nanophotonics allows to reach the quantum ground state of this nanoresonator. By entering in this regime, electro-optomechanical crystals open new avenues for quantum sensing technologies. At the forefront, quantum thermometry is one of the most obvious but also one of the most demanding. Moreover, the coupling between a two-level system (QD, NV center) and such resonator in its quantum ground state would make possible the control of a mesoscopic mechanical resonator with a quantum system and vice versa, thus opening up many perspectives.

• C2N/SPSS - Single photons and single spins

Activités de recherche

Quantum light

Artist view of semiconductor single photon sources: a single quantum dot is positioned at the center of a micropillar cavity that allows for efficient collection of the photons. An electrical control is used to tuned the source wavelength and reduce charge noise.

Quantum light is a key resource for quantum technologies, be it for intermediate scale quantum computing or long-distance quantum communications. However, the development of efficient single photon sources and photonphoton gates remains a great challenge for the scalability of these technologies. In the last few years, semiconductor quantum dots have emerged as a promising system both to generate single and entangled photons as well as to develop deterministic photon-photon gates. Our team has developed a unique expertise in this area, using the tools of cavity quantum electrodynamics and of semiconductor nano-processing. We have developed state of the art single photon sources that allows scaling up optical quantum protocols. We now explore ways to generate new types of quantum bits, perform multiphoton experiments and work toward the generation of multi-photon entangled states. Quandela, a spin-off company funded in 2017, commercializes single photon sources.

Spin-photon interfaces

Schematic of an efficient spin-photon interface, whereby incoming photons experience a strong rotation of their polarization state, depending on the orientation of a single confined spin.

We aim at controlling the interaction between light and matter at the most fundamental quantum level: qubits. To this purpose, we recently developed an efficient interface between a single material qubit (the spin of a single charge, trapped in a nanoscale structure) and a single photonic qubit (the polarization of a single photon). We perform fundamental experiments in solid-state and quantum physics, taking advantage of the quantum backaction induced on a single spin by a single detected photon. We want to entangle a spin with several photons, and perform quantum operations interconnecting photons and spins. Ultimately, our goal is to develop spinmediated photon-photon gates and implement them in various quantum communication and optical quantum computing protocols.

Magnetic quantum dots

Magneto-optical signature of a single InGaAs quantum dot doped by two Mn atoms. Four 2- qubit states |±1,±1> are clearly identified.

As an alternative to the spin of a single charge in a quantum dot (QD), chemical doping by a magnetic atom can be used to introduce a single spin in the QD matrix. When the latter is efficiently coupled to the QD exciton via exchange interaction, it can be manipulated by light. In this research topic, we aim to investigate the system consisting of an InGaAs quantum dot doped by a single or a small number of Mn atoms. Under appropriate magnetic field, these QDs exhibit transitions for both spin manipulation and non-destructive spin readout. The current challenge is to achieve efficient resonant optical excitation of specific transitions, which so far seems to be limited by spectral wandering. We expect significant progress by using optical resonator and better control of the electric environment, in order to demonstrate the potential of Mn-doped QDs for quantum applications.

• MINAPHOT

High quality entanglement on a chip-based frequency comb

Florent Mazeas, Michele Traetta, Marco Bentivegna, Florian Kaiser, Djeylan Aktas, et al.. High quality entanglement on a chip-based frequency comb. Optics Express, Optical Society of America - OSA Publishing, 2016, 24 (25), pp.28731-28738. 10.1364/OE.24.028731. hal-01411319v1

In collaboration with IMPHYNI, we report an efficient energy-time entangled photon-pair source based on fourwave mixing in a CMOS-compatible silicon photonics ring resonator. Thanks to suitable optimization, the source shows a large spectral brightness of 400 pairs of entangled photons /s/MHz for 500 _W pump power, compatible with standard telecom dense wavelength division multiplexers. We demonstrated high-purity energy-time entanglement, i.e., free of photonic noise, with near perfect raw visibilities (> 98%) between various channel pairs in the telecom Cband. Such a compact source stands as a path towards more complex quantum photonic circuits dedicated to quantum communication systems.

Silicon Photonics for Quantum Applications: Coherency-Broken Bragg Filters: Overcoming On-Chip Rejection Limitations

“Coherency-Broken Bragg Filters: Overcoming On-Chip Rejection Limitations” Dorian Oser, Florent Mazeas, Xavier Le Roux, Diego Pérez-Galacho, Olivier Alibart, Sébastien Tanzilli, Laurent Labonté, Delphine Marris- Morini, Laurent Vivien, Éric Cassan, Carlos Alonso-Ramos First published: 15 July 2019 https://doi.org/10.1002/lpor.201800226 Laser an photonics review 13 (8), 1800226 (2019).

Selective optical filters with high rejection levels are of fundamental importance for a wide range of advanced photonic circuits and especially for quantum applications. A new approach based on coherency-broken Bragg filters was proposed to overcome this fundamental limitation on rejection filters. Non-coherent interaction among modalengineered waveguide Bragg gratings separated by single-mode waveguides is exploited to yield effective cascading, even in the presence of phase errors. This technologically independent approach allows seamless combination of filter stages with moderate performance free of active control, providing a dramatic increase of on-chip rejection. Based on this concept, on-chip noncoherent cascading of Si Bragg filters is experimentally demonstrated, achieving a light rejection exceeding 80 dB, the largest value reported for an all-passive silicon filter.

High-quality photonic entanglement out of a stand-alone silicon chip

Schematics of the experimental setup. Raw and net visibilities and internal rate plotted as a function of the signal and idler wavelengths

D. Oser, S. Tanzilli, F. Mazeas, C. Alonso-Ramos, X. Le Roux, G. Sauder, X. Hua, O. Alibart, L. Vivien, É Cassan, and L. Labonté, “High-quality photonic entanglement out of a stand-alone silicon chip,” npj Quantum Inf. 6(1), 31 (2020). https://doi.org/10.1038/s41534-020-0263-7

The fruitful association of quantum and integrated photonics holds the promise to produce, manipulate, and detect quantum states of light using compact and scalable systems. Integrating all the building blocks necessary to produce high-quality photonic entanglement in the telecom-wavelength range out of a single chip remains a major challenge, mainly due to the limited performance of on-chip light rejection filters. In collaboration with IMPHYNI lab, we report a stand-alone, telecom-compliant device that integrates, on a single substrate, a nonlinear photon-pair generator and a passive pumprejection filter. Using standard channel-grid fiber demultiplexers, we demonstrate the first entanglement qualification of such an integrated circuit, showing the highest raw quantum interference visibility for time-energy entangled photons over two telecom-wavelength bands. Genuinely pure, maximally entangled states can therefore be generated thanks to the high-level of noise suppression obtained with the pump filter. These results will certainly further promote the development of more advanced and scalable photonic-integrated quantum systems compliant with telecommunication standards.

Equipes de recherche

• CPHT/ESQM Electronic structure and Quantum Materials

Activités de recherche

Theoretical descriptions of correlated fermionic systems

We conduct research in condensed matter theory, specializing in particular in the electronic structure of materials with strong electronic Coulomb correlations. Coulomb interactions in these materials lead to highly entangled many-body electronic states, the theoretical description of which is a challenging endeavour. Our activities can be regrouped into two classes : First, we develop, refine, implement, benchmark, and apply new theoretical techniques for addressing the subtle quantum correlations governing the behavior of correlated fermionic systems. Second, we work on the theoretical description of specific correlated systems, in order to understand the phenomenology of different correlated fermionic phases of matter, including metal-insulator transitions, various ordering phenomena, disorder-induced effects and many more.

Conceptual and numerical development of new techniques for quantum many-body systems

Cartoon of quantum fluctuations of the charge on a correlated atomic shell in a quantum material.

The theoretical description of interacting quantum many-body systems has seen tremendous progress over the last twenty to thirty years, thanks to the advent of powerful analytical, semi-analytical and numerical techniques such as dynamical mean field theory, improved quantum Monte Carlo, exact diagonalization, cluster perturbation, or renormalisation group techniques. Nevertheless, progress in the field at the same time reveals the need for improved methods able to address various outstanding challenges, such as non-local correlation effects, in particular of collective nature, longrange interactions, multi-orbital physics or disorder effects. These issues are at the heart of our method-developing activities, with the goal of enabling us to address more and more complex correlated fermion physics. Cartoon of quantum fluctuations of the charge on a correlated atomic shell in a quantum material.

Correlated electron physics in quantum materials

Spectroscopy of Sr2IrO4 : experiment vs. theory

Our group has a strong track record of analyzing quantum correlations in transition metal or f-electron compounds, which provide natural applications to the methods we develop. The aim is for example to address response properties and collective phenomena encoded therein, to understand the microscopic mechanisms of metal-insulator transitions (e.g. in VO2 or V2O3), the origin and nature of insulating phases in iridates (see picture), optical properties of f-electron systems, or specifically tailored quantum systems such as adatom systems on surfaces, just to name a few. Many of these activities are run in collaboration with experimental groups, on the Plateau of Orsay-Palaiseau-Saclay and beyond.

• CPHT/AMBP Algorithms for many-body physics

Activités de recherche

Diagrammtic approaches to strongly correlated systems

Poles in the complex plane of the interaction of the Hubbard atom that govern the convergence radius of the perturbation series.

We develop and apply diagrammatic algorithms for the quantum many-body problem. These algorithms aim at computing the coefficients of the perturbation series of given physics observables. Recent years have seen important progress in the development of these approaches. For example, we have been able to compute and resum perturbation series in highly non-trivial regimes of the Hubbard model, thus providing numerically exact results documenting the onset of the pseudogap as observed in hole-doped cuprate superconductors. We plan to pursue these developments and address broken symmetry phases to have deeper insight in the way they compete and lead to unusual physical properties.

Hybrid quantum-classical algorithms

The quantum-classical loop, where the computationally expensive operations are performed by a quantum computer.

In recent years, several prototypes of quantum computers have been developed. If their computing power is still limited, these machines nevertheless allow us to study the potential of quantum computers in different fields of research. A natural field of application is the study of strongly-correlated systems, where the fermionic sign problem is introducing a very severe challenge for classical computer algorithms. We are therefore designing hybrid classical-quantum algorithms to study how efficient they can be at solving the many body quantum problem. These algorithms can readily be tested on the quantum learning machine at ATOS before being submitted on real quantum computers.

• CPHT/QUANT Karyn Le Hur’s « Quantum » group

Activités de recherche

Interactions and Topological Systems

Stochastic approach In reciprocal space

Many-body interacting systems are often difficult to solve. We are developing tools to describe interacting systems with direct applications for topological states of matter. We have studied the phase diagrams of the interacting Haldane and Kane-Mele models, both for fermions and bosons. We are developing a stochastic approach in the reciprocal space with new applications for light-matter systems and quantum transport, which gives good quantitative results for the Mott transition and phase diagram of the Haldane model with the density matrix renormalization group method (see figure with the two phase diagrams). We have shown mathematically how to probe the quantum Hall conductivity from the Dirac points.

Interface Many-Body States and quantum Information Theory

We are developing an interface between many-body quantum states and quantum information theory, introducing tools such as “bipartite fluctuations” with applications in the classification of (interacting) many-body systems and quantum phase transitions through their entanglement properties. Here, the word bipartite refers to the partitioning of a system into two macroscopic entities. We have introduced mathematical series to relate the full counting statistics associated to fluctuations of an observable, such as charge or spin, with the quantum entropies and entanglement spectrum. We have shown applications in quantum matter, mesoscopic systems and quantum optics. We have also shown an application of entanglement to topological states from two Bloch spheres, showing the possibility of rational values of the topological number C for each spin-1/2 in the reciprocal space from the formation of an EPR or Bell pair at one pole (see figure, bottom right).

Theory and Quantum Technology of Light and Circuits

Our theoretical research is also directly related to quantum technology with applications of theory to light systems and quantum circuits. Related to the ANR BOCA with the LPS Orsay and Neel group, we study the mathematics of nano-circulators with applications for topological states and chiral flow of light in Kagome systems (see Figure). Related to the DFG German collaboration FOR2414, we study the implementation of artificial gauge fields and time-dependent drive in optical lattices for new applications. We have shown the applicability of many-body physics in mesoscopic circuits and quantum optics, through the interacting quantum RC circuit and through the Kondo resonance of light, for new quantum interfaces.

• CPHT/QM Quantum Matter

Activités de recherche

The group conducts theoretical research on the dynamics of correlated quantum systems, and more specifically to ultracold atom gases and quantum simulation. Our work aims at characterizing novel quantum phases of matter, understand transport properties of correlated systems, and develop theoretical approaches to this aim. Our work makes use of a wide panel of techniques and, most often, combine analytical approaches (eg. mean field theory, Bethe ansatz, Yang-Yang theory, bosonization, renormalization group analysis, ...) and large-scale numerical simulations for many-body systems (eg. exact diagonalization, path integral quantum Monte Carlo, matrixproduct states, ...).

Quantum phase diagram of a Lieb-Liniger in a quasicrystal potential. From Yao, Giamarchi, and Sanchez- Palencia, Phys. Rev. Lett. 125, 060401 (2020)

• CPHT/MTCM Magnetism and transport in correlated materials

Activités de recherche

Magnetism of strongly correlated d and f-electrons

High rank magnetic order in NpO2 obtained from ab initio exchange interactions. The ordered magnetic moments are of rank 5 (triakontadipole); this order results in a complex distribution of the magnetic density at each Np site as shown in this plot. Different colors indicate 4 inequivalent Np sites.

We study the magnetism of localized f and d shells in realistic oxides and magnetic intermetallics by ab initio methods based on the dynamical mean-field theory. In particular, L. V. Pourovskii proposed a linear response approach to extract exchange interactions between localized degrees of freedom in correlated insulators. This methodology was recently applied to understand the role of high-order (multipolar) exchange in the actinide dioxides UO2 and NpO2, as well as in some transitionmetal oxides and chalcogenides. In hard-magnetic intermetallics the magnetism is determined by interactions of the transitionmetal (Fe or Co) sublattice with the rare-earth one. The state of localized rare-earth 4f shells in those compounds depends on a subtle interplay between exchange and crystal fields as well as on hybridization of 4fs and itinerant states. We treat those competing energy scales from first principles, obtaining macroscopic quantities like magnetization and anisotropy constants. We aim at elucidating the role of hybridization effects in crystal-field splitting and their impact on the magnetocrystalline anisotropy in various perspective hardmagnets, like, for example, SmCo5, Nd2Fe14B, NdFe12. The role of complex many-electron effects, i. e. the Kondo effect, is the focus of research in magnetic Ce-based systems.

Electronic correlations and transport in the inner core matter

Thermal conductivity of iron at the inner core temperature (6000 K) vs. increasing degree of lattice disorder. Realistic thermal disorder in the core is indicated by vertical dashed line. Squares are the condictiviy predicted by our ab initio calculations. Shaded regions indicate the conductivity values corresponding to two models for the evolution of inner core.

Dynamics of the deep Earth interior is strongly influenced by transport properties of the core matter. In particular, Earth magnetic field is generated by a thermal convection of the conducting liquid core. The main constituent of Earth’s core is iron; the thermal conductivity of iron has thus direct impact on the geodynamo mechanism. This metal may exhibit significant many-electron correlations, contributing through electron-electron scattering to its electric and thermal resistivity. The conductivity of solid iron also impacts the dynamics of the inner solid core. We study those properties using the ab initio dynamical meanfield theory. In particular, the role of electron-electron and electron-lattice scattering in iron under inner core conditions has been evaluated in a recent work. We find the electron-lattice scattering to be the primary contribution into the overall resistivity, which is predicted to be rather low, favors the hypothesis of a young (< 1 Gy) solid inner core of Earth. The impact of many-electron effects on thermodynamic stability of different solid iron phases at the inner core conditions is a direction for future studies.

• CPHT/TCM Theory of complex materials

Activités de recherche

Order parameters of structural and magnetic phase transitions

The antiferroelectric distoriton in the low temperature phase of Ta2NiSe5.

Phase transitions can be easily observed in experiments that measure thermodynamic quantities such as heat capacity and magnetic suceptibilities. However, experimentally determining the order parameters of phase transitions can often be challenging. We use first principles calculations to identify the structural and magnetic instabilities. In LaNiO3, we calculated total energy as a function of magnetic orderings to propose an unusual antiferromagnetic order parameter for the low-temperature magnetic phase. In Ta2NiSe5, we calculated the phonon dispersions to propose an antiferroelectric distortion as the order parameter for the low-temperature phase.

Thermal conductivity of binary and ternary oxides

The three-phonon scattering phase space in different binary and ternary oxides.

There is an intense search for materials that break the current known limits of thermal conductivity at both the high and low ends of the scale. We are trying to identify binary and ternary oxides that are highly efficient in conducting heat by calculating their thermal conductivity using three-phonon scattering rates obtained using density functional theory and the solution of the Boltzmann transport equation.

Light-control of materials via nonlinear phononics

Pumping an infrared active phonon mode can cause the Raman active phonon mode to vibrate at a displaced position.

We are collaborating with the experimentalists at the University of Rennes to control the physical properties of organic crystals by pumping their infrared active phonon modes using intense laser sources. The crystal structure displaces along the coordinates of lowfrequency Raman modes after the laser pump due to nonlinear coupling between the infrared and Raman active phonon modes. We are trying to understand the light-induced dynamics in the experiments being performed at Rennes.

• CPHT/CTQM Computational Theory of Quantum Matter

Activités de recherche

Computational methods for quantum systems with strong correlations

The wave-function of a quantum many-particle system lives in an exponentially large Hilbert space.

The quantum `many-body’ problem is a fundamental problem of both applied and fundamental importance. Our team develops novel algorithms to deal with this computationally complex problem, using in particular `quantum embedding’ methods such as extensions of dynamical mean-field theory. We also aim at a `handshake’ with other methods, such as tensor-network neural network representations of wave-functions. These methods are applied to both materials and other quantum systems such as cold atoms in optical lattices.

Quantum Materials with Strong Electronic Correlations

A model quantum material and unconventional superconductor: Sr2RuO4

Material with strong correlations between electrons display a large range of fascinating collective phenomena, such as magnetism, superconductivity, metal-insulator transitions etc. Our team combines electronic structure methods with advanced quantum many-body methods to compute and understand the physical properties of these materials (such as transition-metal oxides, high- Tc superconductors or twisted bilayer graphene).

Materials in Quantum Cavities

Two-dimensional quantum material in a QED cavity

We are exploring how the properties of quantum materials can be modified by coupling their internal degrees of freedom to the photons of an electromagnetic cavity.

Equipes de recherche

• ONERA/DOTA

Activités de recherche

Le Département optique et techniques associées de l’ONERA réalise des études et recherches appliquées principalement aux domaines de l’aéronautique, l’espace et la défense, et à d’autres tels que la sécurité, l’environnement, l’astronomie, ou l’imagerie médicale. Nos travaux impliquent des méthodes et des outils communs à l’optique quantique ou la physique atomique, illustrant le bénéfice des interactions entre physique classique et quantique. Nous cherchons par ailleurs à identifier des méthodes quantiques applicables à nos activités actuelles, ainsi que les nouvelles applications potentielles des technologies de l’optique quantique.

Equipes de recherche 

• ONERA/CIAP Capteurs Inertiels à Atomes Froids

Activités de recherche

The Cold Atom Inertial Sensors team at ONERA has been pursuing efforts towards the development of transportable cold atom gravimeters for more than 15 years. To date, their instrument is the only quantum sensor able to measure gravity in operational environments. Several shipborne and airborne measurement campaigns have been performed, demonstrating equal or better performance than classical gravimeters. Recently, ONERA has started important efforts to build a small industrial series of this instrument, while transferring the technology to the French company Muquans. Longer-term research efforts include cold atom gyroscopes and multi-axis accelerometers, interferometers with multiple atomic species and arrays of single Rydberg atoms for microwave sensing and quantum metrology.

The « GIRAFE » transportable cold atom gravimeter by ONERA

Equipes de recherche 

• GEMAC/OEN Optique à l’échelle nanométrique (OEN)

Activités de recherche

Collective effects - Gold-semiconductor hybrid nanoparticles (OEN, collaboration : LCF)

Illustration of an ensemble of NCs encapsulated into a gold shell

The OEN team is carrying out work devoted to the optical characterization of a new type of hybrid fluorescent emitters combining colloidal nanocrystals (NCs) with plamonic nanoresonators. We have already investigated the emission of individual spherical or two-dimensional colloidal NCs (nano-platelets, NPs) encapsulated in a silica layer and covered by a gold shell by solution chemistry methods. Beyond the study of individual emitters, the work focuses on the coupling of an ensemble of NCs or NPs to plasmonic cavities and the study of collective effects (superradiance, strong coupling) to enhance the light emission of these superparticles.

Coupling single photon sources with photoresist photonic structures (OEN, collaboration : LuMIn)

Illustration of CdSe/CdS NCs coupled into dielectric nanopillar antennas

In collaboration with Ngoc Diep Lai of LuMIn, we are working on the integration of chemically synthesized individual colloidal semiconductor nanocrystals (NCs) into photonic structures made in a photoresist (SU8) by an original technique called LOPA for Low One Photon Absorption. By exposing the polymer to a focused laser at 532 nm, it is possible to define 3D architectures with a resolution well below 200 nm. The LOPA technique has already been used to fabricate various 2D structures containing NCs (nano-antennae, bull-eye cavities...). We are currently seeking to extend this appoach to 3D structures and NV centers in diamond.

Nanostructures and colour centres (OEN - DIAM - NSP, collaboration : RCFM, LEM)

Array of single photon emitters generated in a hBN nanoflake

ZnO nanowire

Colour centres are optically active deep defects in the condensed matter. They represent a major interest in quantum information science, owing to their potential as single photon emitters, as well as to the possibility to integrate them in solid-state nanostructures and devices. This research topic is focused on the study and quantum engineering of colour centres in wide gap materials such as hBN and ZnO. The emphasis is put in particular on defects that can be controllably created or activated in semiconductor nanostructures, as well as the realisation of miniaturised devices, with electrical and optical functionalities (microcavities, plasmonic resonators, waveguides). 

• GEMAC/DIAM Diamant pour l'électronique (DIAM) 

Activités de recherche

Atomic defects in wide bandgap semiconductors (DIAM, collaboration : Thalès, LEM, SSSG, Felix Bloch) The activities of the DIAM team focus on the defects in semiconductors and in particular on the color centers in diamond and hexagonal boron nitride (hBN). We fabricate diamond thin films by homoepitaxy: doped with phosphorus and isotopically purified to stabilize and increase the coherence of NV spins. The NV centers implanted by focused ion beams (FIB) for quantum applications are studied in cathodoluminescence (CL) at the nanometer scale. The expertise of the DIAM team on 2D semiconductors has allowed to start researches on color centers in hBN in collaboration with the OEN team (next topic). They are activated by electron irradiation to allow the study of quantum properties of isolated centers.

NV center interactions with phosphorus impurity and carbon 13 nuclear spin in diamond.

• GEMAC/NSP Nanostructures Semiconductrices et Propriétés (NSP)

Activités de recherche

Nanostructures and colour centres in ZnO (collaboration OEN)

Pour en savoir plus 

Equipes de recherche

• I2CB/LBMS (Laboratoire de Bioénergétique Membranaire et Stress)

Activités de recherche

L’équipe s’intéresse aux étapes primaires de la photosynthèse (transfert d’excitation et transferts de charges, ayant lieu dans les 20 premières picosecondes après l’absorption du photon par un pigment spécialisé), et à leur caractère quantique en particulier. Plus généralement, l’équipe s’intéresse aux phénomènes de photobiologie, en particulier à la fission singulet ayant lieu dans les assemblages biologiques.

Equipes de recherche

• IPHT/QI Quantum information : applications to quantum computing and quantum communications

Activités de recherche

Quantum computations

Quantum circuit for quantum computation

We work both on the development and on the characterization of novel architectures for quantum computations. We are in particular interested in the performance of new architectures to solve problems relevant in quantum chemistry. In parallel, we work on designing algorithms which could be used on hybrid machines combining a classical high performance computer and a small noisy quantum unit.

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Equipes de recherche

• ISMO/DIRAM

Activités de recherche

Cold atom-based quantum sensors (E. Charron)

A Bose-Einstein condensate was created for the first time in space by a team of physicists from the University of Hanover (Germany), in collaboration with theoretical physicists from ISMO (University Paris-Saclay & CNRS, Orsay, France).

Quantum physicists have a strong interest in reaching very low temperatures to explore new states of matter. The advent of quantum gas cooling marked a new era in this field. The ultimate potential of these very low temperature systems is revealed when they are probed in free evolution over long periods of observation. Space exploitation, where quantum matter can float freely for long periods of time, is at the forefront of this quest for low energy and its exploitation. We explore these regimes by developing a precise quantum control of the physical properties of atomic gases. The engineering of these states has many applications for quantum information processing, quantum simulation as well as for metrological applications such as Earth observation, relativistic geodesy or tests of the fundamental laws of physics. Reference: D. Becker et al, Nature 562, 391 (2018).

Laser control of ultra-cold molecules (O. Atabek)

STIRAP and chirp strategies for creating molecules in their absolute ground state taken from a work in collaboration with LAC and ICP (University Paris-Saclay & CNRS, Orsay, France)

Ultra-cold molecules are promising systems for a wide range of applications, including quantum simulation and computation and precision measurements. We are developing and studying strategies, based on laser control, for the preparation of such systems by photo-association. A first class of strategies creates a Feshbach resonance whose decay is controlled by ZWR (Zero- Width Resonance) while the population is transferred to an excited vibrational state of the molecule. A second class uses a STIRAP process to achieve this same transfer. The final transfer to the fundamental level is done by experimentally proven techniques (STIRAP, chirp) or techniques in development (e.g., ZWR, Exceptional Points). Reference: R. Lefebvre, O. Atabek, Phys. Rev. A 101, 063406 (2020)

Quantum technologies and Molecular dynamics (F. Gatti)

Coherent control of photochemical processes

It is about describing and controlling chemical reactivity at a microscopic level through the systematic use of quantum phenomena such as quantum coherence. The use of coherent wave packets can be seen as a paradigm shift in chemistry with extensions to biology. It is now possible to describe the molecular quantum dynamics of large systems. The most recent experimental developments open up the possibility of controlling the movement of electrons and nuclei, each of them on its natural time scale. It thus becomes possible to “operate on” molecular systems controlling all the different aspects of the system as in a kind of “chemical surgery” by a “photonic scalpel”. Reference: F. Gatti, Nature, New & Views, 557 (7707), 641-642.

• ISMO/Nanobio

• ISMO/NanoPhys

Activités de recherche

Optical Field Emission and Ultrafast Electron Transport in Plasmonic Gaps

Manipulating electrons with light in nanoscale plasmonic gap structures

The possibility of engineering enhanced optical fields in narrow-gap plasmonic nanoantennas allows one to reach the optical field emission regime and to drive femtosecond electron currents in the gap with single-cycle optical pulses. We develop theoretical tools based on one-electron and many-body quantum time-domain approaches that enable one to access the optical field emission as well as the dynamics of the emitted electrons in the plasmonic gaps. We are particularly interested in the possibility of achieving active control of the electron transport in nanodevices. These may consist of a plasmonic gap antenna connected to an external circuit. The results could lead to applications in ultrafast petahertz electronics.

Electrically driven single photon nanosources

Single photon nanosource consisting of a semiconductor nanocrystal in the gap of a bowtie antenna

We are working towards using the inelastic tunneling current in metal-insulator-metal or metal-insulator-semiconductor systems to drive single photon nanosources. These may be based on semiconductor nanocrystals or induced defects in 2D materials. Plasmonic materials will be used to enhance and control the emission properties of the single photon nanosource.

Nanoscale devices on silicon surfaces

Top: STM image of a 4 quantum dot star shape that has the properties of an ON/OFF switch. Bottom: Association of two Er adatoms on an Si(100) surface.

One of the activities of the MND axis in the Nanophysics and Surfaces group at ISMO is devoted to the study of nanoscale devices on silicon surfaces. A part of this study concerns quantum dot interactions that can be considered as silicon qubits. The properties and interactions of these qubits are studied via electronic excitations induced with the tip of an STM/AFM at low temperature and via the analysis of their luminescence. Another aspect of this research is related to the study of the optoelectronic properties of atomic-scale lanthanides on a silicon surface. We aim to use the long lifetime of the 4f orbitals of these species to optically excite and entangle different levels of various ionic species when adsorbed on silicon surfaces.

• Sysiphe

Activités de recherche

Vibrational coherence / Cohérence vibrationnelle

Montage expérimental

Study of vibrational coherence times of molecular systems trapped in cryogenic solids – Environment effects on decoherence processes. Following our IR photon echo work, we perform multidimensional infrared spectroscopy in cryogenic matrix – degenerate four-wave mixing method – with the aim of reaching resolutions better than cm-1, thereby accessing long coherence times (> 100 ps).

EDM (electric Dipole Moments)

We participate to the Matrix EDM project, initiated at LAC. Electric dipole moments (EDM) of electrons, neutrons or nuclei are probes of particle physics beyond the standard model. The proposal consists in measuring the EDM of electrons using impurities embedded in a cryogenic solid matrix of inert gas or hydrogen. The matrices offer unprecedented sample sizes while retaining many features of an atomic physics experiment, such as laser manipulation. By using atoms and molecules (Cs, Yb, BaF ...) in an argon or parahydrogen matrix, we want to study the principle of EDM measurement through a precise study of systematic effects that would then allow to reach an unprecedented accuracy. (collaboration between LAC, ISMO, CIMAP and LPL)

• SIM2D

Experimental studies of the electronic structure of functional quantum materials

Systems with strongly interacting electrons present competing quantum ground states from which a rich variety of remarkable macroscopic properties emerge. Many of these materials are challenging from a fundamental standpoint, while their functionalities are promising for applications. We study experimentally their quantum electronic structure using angle-resolved photoemission spectroscopy (ARPES).

Electronic, magnetic & optical properties of functionalized 2D materials

2D materials have been at the forefront of research over the last decade. Following the discovery of graphene, new 2D materials have been discovered. Silicene, phosphorene, bismuthene and metal tellurides are particularly interesting because reducing the dimensionality reveals new electronic, magnetic and optical properties.

Structural and electronic properties of surfaces using GIFAD

After discovering that fast (keV) atoms can diffract on crystal surfaces, we have developped the technique. It can image large dimensions of the crystal surface with a resolution reaching 10 pm. The inelastic component highlights surface defects (steps, ad-atoms) and dynamical aspects of the surface (vibrational excitations, electron-hole pair creations..)

• ISMO/SYSTEMAE

- Dynamique électronique en présence de quantum dots

- Study the structure and the spectroscopic response of hydrocarbon molecules present in the interstellar medium through computational methods

- Contrôle des degrés de liberté moléculaire à l'aide d'impulsions laser ou térahertz. Sont concernés les degrés de liberté externe de molécules rigides et les degrés de liberté interne de molécules nonrigides. Les phénomènes ciblés vont de l'orientation à l'alignement en passant par les échos. La manipulation de la torsion de molécules axiales chirales est également étudiée avec pour objectif l'enrichissement énantiomérique.

Equipes de recherche

THEOMOL :

Equipe composée de théoriciens-ennes en physique atomique et moléculaire, en dynamique quantique, et interaction matière rayonnement pour le contrôle quantique.

MFC (Matière Froide Corrélée) :

Equipe composée d’expérimentateurs experts en refroidissement, guidage et piégeage d’atomes et de molécules, et de sources d’ions et d’électrons lents.

Equipes de recherche

• LAMBE/THY Théorie et Modélisation


Activités de recherche

Spécialiste de Chimie théorique et computationnelle. Dynamiques moléculaires ab initio/quantiques de mol cules et clusters en phase gazeuse, de liquides, d’interfaces non homogènes solide/liquide.
Expertises en spectroscopies vibrationnelles de la matière condensée, théorie de ces spectroscopies.
Recherche bi-disciplinaire simulations numériques et algorithmiques de graphes/méthodes de machine learning/IA.

Equipes de recherche

• LARSIM

Activités de recherche

Indefinite causality

Indefinite causal orders – a non-classical resource based on the indefinite nature of causal relations between operations in Hilbert space – provide a quantum advantage demonstrably different from that of superposition. Recent theoretical and experimental work focused mainly on a causally indefinite process called the “quantum switch”. It provides several advantages over standard models of quantum information processing, showing that causal indefiniteness is a useful new resource for quantum information processing tasks, and one that is, moreover, experimentally relevant. Larsim (team led by A. Grinbaum) has been involved in research on causal indefiniteness since 2013, working on entropic measures and studying the computational advantage of the quantum switch versus superposition.

Contextuality as quantum resource

Bell's inequalities and the Kochen-Specker theorem provided rst tangible assessments of nonclassicality. John Wheeler's dictum “It from Bit" marked the birth of an approach using such quantitative measures to perform classically impossible tasks. On this view, quantum theory employs classically unavailable protocols or resources. Quantum theory is seen as a “resource theory", and the resources are consequently exploited by quantum technologies in order to build real-world non-classical devices. At Larsim, we explore models of generalized postquantum contextuality to better understand this non-classical resource and the communication advantage that it provides.

Information-theoretic interpretations of quantum mechanics

The philosophical interpretation that “quantum physics is about information" has emerged as a logical consequence of new mathematical results in the foundations of quantum mechanics and quantum information. The concept of information can be understood in various ways, based on the Shannon, von Neumann, or Kolmogorov entropies, but also incorporating such quantum features as the possibility to continuously vary one's information state. At Larsim (A. Grinbaum), we work ono such “informational" interpretations and corresponding axiomatic approaches to quantum mechanics. This work has produced a new wave of operational accounts, while also contributing to the emergence of a particular informational form of structural realism.

Equipes de recherche

• LCF/QO-A Quantum Optics - Atoms 

Activités de recherche

Quantum simulation using arrays of single Rydberg atoms

In this research activity, we use arrays of optical tweezers, each containing a single rubidium atom, and we induce strong, controlled interactions between the atoms by exciting them coherently to Rydberg states (highly excited states of the atom, that interact strongly via electric dipole-dipole interactions). We have full control over the system: geometry, dimensionality and size of the arrays, exact number of atoms, strength of the interaction… With this platform, we explore the physics of spin Hamiltonians (Ising or XY models, synthetic topological matter) with up to 200 particles.

A square array of individual rubidium atoms held in optical tweezers. The distance between neighboring atoms is 10 μm.

Collective light-matter interaction in structured atomic ensembles

This research focuses on the experimental study of the collective interaction of light with ensembles of cold atoms. By shining laser light onto a dense cloud or structured array of laser-cooled atoms, dipole moments are induced in the atoms, and the dipolar interactions between those induced dipoles strongly alter the atomic response to light when the atoms are separated by subwavelength distances. This results in a quantum many-body driven dissipative system with non-trivial properties both for the atoms and the scattered light.

Sketch of the experimental setup with two orthogonal high-resolution optical systems allowing the trapping and observation of atoms.

• LCF/QO-NCS Quantum Optics – Non-Classical States Generation

Activités de recherche

Generation of non-classical states of light

Quantum optics provides useful tools for quantum information processing. In the continuous variables approach, some "exotic" states with complex quantum structures exhibit interesting quantum properties, opening new perspectives. We are working on new concepts for the generation of such states: we presented the first implementation of a “cat breeding” scheme, with the generation of optical "Schr dinger cat" states by the coalescence of two photons. We have recently developed a high-rate single photon source, coupled to a quantum memory in order to deliver the photons on demand. Such a setup could considerably improve the production rate of the abovementioned breeding scheme.

Wigner function of a "cat" state generated by photon coalescence.

• LCF/QO-FQC Quantum Optics – Foundations and Quantum Cryptography

Activités de recherche

Quantum cryptography with continuous variables

Quantum cryptography with continuous variables (CVQKD) has been introduced by our group in 2003 (F. Grosshans et al, Nature 2003). It is also called GG02 protocol (Grosshans-Grangier 2002), and is now implemented by many groups worldwide. We are pursuing it within the framework of one European Flagship project, CiViQ (2018-2021, 10 M€), specifically dedicated to CVQKD, and of another large European project, OpenQKD (2019- 2022, 15 M€), gathering most of the European effort on QKD. This work is done in collaboration with LIP6 at Sorbonne Universit  (Eleni Diamanti), Nokia Bell Labs France (Nozay), Ixblue (Besan on), and Thales (TRT and SIX).

CVQKD setup with Mistral encryptor developped by LCF, Thales and LIP6 (ANR SEQURE, 2012).

Foundations of quantum mechanics

Following theoretical work done by Philippe Grangier in 2000- 2002, we have recently developed a new framework for Quantum Mechanics, called “Systems, Contexts and Modalities” (CSM). This work has been done in collaboration with Alexia Auff ves (Institut N el, Grenoble) and Nayla Farouki (philosopher, previously advisor at CEA). We have published a significant series of articles, including broad audience ones (e.g. Journal du CNRS, La Recherche…), and our results have also been presented in many national and international conferences. They continue developing on both the physical and the philosophical sides, and all articles are available on arxiv.

Generic scheme for experimental test of Bell’s inequalities, which are at the core of the discussions on the foundations of Quantum Mechanics (A. Aspect et al, 1981-82).

• LCF/QG-QAO Quantum Gases : Quantum Atom Optic

Activités de recherche

Bose Einstein condensates of metastable helium are used to test Bell’s inequalities. This test will be the first using massive particles entangled in their motional degrees of freedom.

Schematic diagram of the protocol used to observe two particle interference. Interference is detected in the correlations between detectors it the A and B outputs. High enough fringe contrast can lead to violation of a Bell inequality.

Quantum simulation of the early Universe

We seek to observe entanglement in bi-partite phonon states for the dynamical Casimir effect – as well as the onset of decoherence and nonlinear effects. From a conceptual point of view, a clear result demonstrating entanglement and its subsequent disappearance would help clarify much of the conjectural physics involved in modeling cosmological processes. We thus have a fascinating example of quantum simulation, in which a laboratory experiment can shed light on a complex system – in this case, the very early universe – about which we are unable to make reliable predictions and which is poorly accessible to observations.

Illustration of a laser trap whose depth is temporally modulated to create phonons with an energy of the modulation frequency.

• LCF/ QG-LG Quantum Gases : Lattice Gases

Activités de recherche

Etats corrélés sur réseaux – Hamiltonian de Bose-Hubbard et transition de Mott

We load a gas of metastable Helium-4 atoms into a 3D optical grating and study the equilibrium properties of the Bose-Hubbard model from a single measurement, the 3D velocity distribution. We have studied the phase diagram (superfluid to Mott transition, superfluid state to normal gas transition) and the possibility of creating correlated states in the critical regime of the Mott transition.

Phys. Rev. A 97, 061609(R) (2018) Phys. Rev. Research 2, 013017 (2020) Arxiv 2010.14352 (2020)

Certifying the adiabatic preparation of strongly correlated states of the Bose-Hubbard Hamiltonian (at a constant entropy of 0.8kB per atom)

Corrélations en vitesse entre atomes individuels

The large internal energy stored in the metastable state of Helium-4 atoms allows individual detection of these atoms in the velocity space. From the recorded three-dimensional distributions, we measure the correlations between an arbitrary number of individual atoms (g(2)(k,k'), g(3)(k,k',k''), ...). Such measurements, inspired by Quantum Optics, are used to study highly correlated systems, such as those of interacting particles in a periodic potential.

Phys. Rev. X 9, 041028 (2019) Phys. Rev. Lett. 125, 165301 (2020)

Momentum-space correlations between three individual atoms in a Mott insulator

• LCF/GG-DQG Quantum Gases : Disordered Quantum Gases with Tunable Interactions

Activités de recherche

Bose gases with tunable interactions

We study gases in reduce dimensions (1D, 2D), where quantum and thermal fluctuations are most important. Importantly, we work with potassium 39, a bosonic element having nice magnetically tunable Feshbach resonances, thus permitting the control of the interatomic interaction.

Propagation of 39K bright solitons.

We can add a controllable amount of disorder thought a speckle light field. Disorder competes with the interaction induced superfluidity. For example a superfluid to insulator transition is observed in 2D Bose gases. We can also study non-interacting phenomena such as Anderson localization, i.e. the absence of diffusion due to multiple quantum interference. Recently, we have studied the superfluid propagation in a 1D disordered trap of bright solitons; condensed clouds of atoms which remain together because of attractive interaction.

Schematic of the experimental sequence. A non-interactiing BEC is launched in a 1D speckle potential. At intermediate disorder strength, both localized and propagating atoms are observed.

• LCF/QG-QDN Quantum Gases : Quantum dynamics in N-body systems

Activités de recherche

Our team investigates the relaxation dynamics of quantum many-body systems with ultracold strontium gases. Thanks to a recently built microscope for quantum gases, we aim at solving two distinct problems:

(i) Under what conditions will an isolated quantum system set out of equilibrium relax towards a thermal state? In other words, what makes a quantum system ergodic?

(ii) Can we identify universal features in the the relaxation dynamics itself?

The aim is then to understand how correlations build up between two initially uncorrelated regions of space and to which extent their equilibrium value depends on the initial conditions imposed on the system.

The ultracold strontium gas trapped inside a vaccum chamber.

• LCF/QG-QT Quantum Gases : Quantum transport in disorder

Activités de recherche

Our team studies the transport properties of matter waves in well controlled disordered potentials, focusing especially on the celebrated Anderson localization. Landmark results has been obtained in the team, such as the direct observation of 1D and 3D Anderson Localization or Coherent Backscattering (which is a direct signature of phase coherent effect in disorder media). Using a novel method (based on spectroscopy) our current goal is to investigate in detail the Anderson transition that occurs in 3D, which constitutes an utmost challenge in the field.

Experimental observation of atoms localized in a speckle disorder. The atomic density exhibits an exponentially decreasing density (in green).

• LCF/QG-AC Quantum Gases : Atom Chips

Activités de recherche

Physics of one-dimensional Bosons gases.

We study both equilibrium and out-of-equilibrium properties. We study in particular the role of integrability in these N-body quantum systems.

Chip used to make and study one-dimensional gases: the atoms are confined in magnetic traps made by microwires deposited on the chip. The micro-wires are covered with a mirror.

• LCF/PNQ Plasmonique et nanophotonique quantique

Revisiting Quantum Optics with single surface plasmons

Surface plasmons are waves of electron density propagating at the interface between a metal and a dielectric. They confine the electric field in a tiny volume, and this property makes them particularly interesting candidate to convey optical signal through nanometric structures and devices that are much smaller than conventional optics. Moreover, theoretical models predict that the quantum behavior of plasmons is identical to the quantum behavior of photons. Thus, many physicists nowadays study the opportunity to use plasmons instead of photons for quantum information related applications. Quantum plasmonics aims at reproducing experimentally the landmark experiments of quantum optics using single surface plasmons. One of the most famous of these experiments has been performed around 30 years ago by Hong, Ou and Mandel : they observed that two indistinguishable photons reaching a 50/50 beamsplitter using two distincts input ports would exit the same device by two separated output ports, a phenomenon since called photon coalescence. Our team performed a plasmonic version of the HOM experiment and we could observe both the coalescence but also an anti-coalescence effect in specific conditions. We also investigated a variety of other situations, such as the hybrid antanglement between a plasmon and a photon, the non-local control of a plasmon state, or the observation of plasmonic N00N fringes.

Publications: Anti-coalescence of bosons on a lossy beamsplitter

Science Vol. 356, Issue 6345, pp. 1373-1376 (2017)

A: Directional photon-plasmon coupler, B: Plasmonic chip including two couplers a surface plasmon beam splitter and two outcoupling slits. C: lateral view of the plasmonic chip.

Antenna Surface Plasmon Emission by Inelastic Tunneling (ASPEIT)

Surface plasmons polaritons are mixed electronic and electromagnetic waves. They have become a workhorse of nanophotonics because plasmonic modes can be confined in space at the nanometer scale and in time at the 10 fs scale. However, in practice, plasmonic modes are often excited using diffraction-limited beams. In order to take full advantage of their potential for sensing and information technology, it is necessary to develop a microscale ultrafast electrical source of surface plasmons. Here, we report the design, fabrication and characterization of nanoantennas to emit surface plasmons by inelastic electron tunneling. The antenna controls the emission spectrum, the emission polarization, and enhances the emission efficiency by more than three orders of magnitude.

Antenna Surface Plasmon Emission by Inelastic Tunneling

C. Zhang, J.P. Hugonin, A.-L. Coutrot, C. Sauvan, F. Marquier, J.-J. Greffet, Nat Commun 10, 4949 (2019)

Plasmonic antenna for electrical emission of surface plasmons

Controlling spontaneous emission at the nanoscale

A basic paradigm of light emission is the radiative relaxation of a two-levels system. The emission process can be controlled by modifying the emitter environment. There are basically two ways of modifying the environment and this is also true for an acoustic wave emitter: the source can be placed in a cavity (e.g. a piano string alone or close to the piano resonator), the source can be placed near another source thereby generating so-called collective effects (e.g. two piano strings or two organ pipe). We explore the interplay between these two effects two generate non-classical states of light.

Single photon emission by two dipoles strongly coupled by the dipole-dipole interaction in a cavity.

Equipes de recherche

• LIDYL/PH1 PHI-EXQUESITE (au sein de l’actuel groupe PHI)

Activités de recherche

Strong-Field Quantum Electrodynamics at extreme light intensities

We are developing new concepts to very soon reach unexplored regimes of strong-field Quantum Electrodynamics (SF-QED) with currently available high-power Petawatt (PW) lasers. Such regimes occur at extreme light intensities, the most famous example being the optical breakdown of the quantum vacuum occurring beyond light intensities of 10²⁹W/cm² (the so-called Schwinger limit). Reaching these regimes would have major impacts on (i) the test of Quantum Field Theory in yet unexplored regimes (ii) the potential discovery of new physics beyond the standard model (axions, millicharged particles) (iii) the understanding of extreme astrophysical events involving SF-QED processes and (iv) the design of future lepton colliders.

As the Schwinger limit is 7 orders of magnitude higher than the present record in laser intensity (5x10²²W/cm²) set by a 4PW laser, it is impossible to reach with conventional optical laser technology and new paradigms are absolutely necessary to close this gap. To break this barrier, our approach consists in directly boosting the intensity of a PW laser pulse upon reflection off a curved relativistic plasma mirror. A relativistic plasma mirror can be formed by the PW laser pulse itself after focusing on an initially solid target.

In this context, our main experimental and theoretical activities currently focus on:

(i) The development of realistic all-optical techniques to efficiently curve the surface of a plasma mirror in experiments,

(ii) the development of new numerical tools at exascale to efficiently simulate light-matter and light-vacuum interactions in our kinetic code,

(iii) the identification of clear SF-QED signatures (antimatter particle beams and hard radiations) with our code that will be essential to guide planned experiments on PW laser facilities.

3D Kinetic simulation (with our code WARPX+PICSAR) at intensities >1025W/cm2 for which SF-QED processes dominate the light matter interaction. This simulation shows prolific electronpositron pair production (green/violet) induced by the SF-QED non-linear Breit-Wheeler process occurring in a secondary target (grey scale) placed at the focus of a Curved Relativistic Plasma Mirror. The simulation was performed on the SUMMIT GPU Cluster at the Oak Ridge Leadership Computing facility.

• LYDIL/ATTO AttoPhysique

Activités de recherche

Attosecond dynamics of small quantum objects

Using attosecond (1 as=10⁻¹⁸ s) pulses of XUV light, we investigate ultrafast electronic dynamics in small quantum systems: atoms, molecules, clusters, nanoparticles. Attosecond spectroscopy allows studying fundamental processes, e.g., photo-ionization, giving access to photoemission delays - or Wigner delays - as well as more complex dynamics close to resonances. Spatially and temporally resolved measurements provide insight into electron correlation, in particular to electronic rearrangements in the ion upon electron ejection. The control of the charge migration in bio-relevant molecules opens the prospect of a charge-directed reactivity in attochemistry. Finally, we investigate quantum decoherence effects, e.g., induced by ionphotoelectron entanglement.

Experimental reconstruction of the temporal buildup of the 2s2p autoionizing resonance of Helium in the photoelectron spectrum

Femtosecond laser induced topology

We propose to exploit the best aspects topology to avoid energy losses in electronic transport. Laser electronics would make it possible to overcome the limitations imposed by the properties of quantum materials in order to create new storage functionalities (“write” function) and information processing (“read-out” function and associated algorithms). We will use the latest technologies in 2D materials, ultra-fast electron and X-ray spectroscopy, and attosecond science, nanotechnology and quantum computing. In order to realize this platform, we need to control structured light (orbital angular momentum), to write / read topological states, possibly at optical cycle speeds (THz-PHz), to store and process quantum information. We will focus on the induction and manipulation of topologically protected states by temporally and spatially structuring light pulses to transfer moment and spin to a 2D hexagonal material. Optical vortex beams offer also a fantastic opportunity to circumvent these difficulties by transferring their orbital angular momentum (OAM) to magnetic materials. The coupling between photon magnetic fields and local magnetic moments can be used to create complex solitons (skyrmions).

Artistic view of a laser beam carrying orbital angular momentum to create a skyrmion.

Equipes de recherche

• LISN/PARSYS

Activités de recherche

High performance quantum computing

Even though Exascale will undoubtedly represent a technological and algorithmic advance, some critical scientific computations will remain out of reach of conventional supercomputers. For some of these (e.g., simulations for optimizing molecule synthesis) quantum computing is a promising track for speeding up the computations. Quantum computing and its potential usage is currently under study by major actors of Computer Science, such as BULL, IBM, Microsoft, Google, etc.

Our research concerns the development of algorithms and software for future quantum processors including for instance:

• Optimization of quantum circuits via linear algebra specific algorithms
• Application of quantum computing to scientific computing (e.g., tensor computations, solution of PDEs) and data analytics (e.g., machine learning,data clustering)
• Simulation of quantum algorithms on massively parallel architectures.
• Exploration of interactions between classical and quantum computing at the theoretical and practical level.

Equipes de recherche

• LIST/Quantum

Activités de recherche

Pile logicielle quantique

Cette activité  de recherche s’attache  étudier la chaine de programmation des algorithmes quantiques et de leur intégration dans un flot de programmation et d’exécution hybride classique/quantique. Dans ce thème on étudie en particulier les phases de spécification, de modélisation, d’identification des noyaux de calculs pour le quantique et leur impact sur la compilation et amont sur les méthodes et les outils de programmation  mettre en oeuvre. Un volet important des recherches dans ce thème concerne la vérification de programmes quantiques qui s’attache  vérifier que les circuits quantiques issus de la compilation de programmes haut niveau implémentent correctement les fonctions souhaitées.

Co- développement de l’interface au matériel

Cette recherche consiste  co-développer les interfaces entre logiciel et mat riel qui autoriseront l'exécution d'applications sur une cible concrète. Il s’agit ainsi de lier la "pile logicielle" étudiée dans le premier thème avec une "pile d'exécution" chargée de l'orchestration des circuits physiques, du contrôle des qubits et des méthodes et circuits de mesures. Cette recherche s’intéresse aussi aux couplages entre circuits quantiques et classiques pour l’implémentation efficace d’une architecture de calcul quantique nécessairement hybride.

Evaluation applicative de l’avantage quantique

Ce thème d’études cherche  à évaluer l’avantage potentiel d'une approche quantique sur des applications concrètes dans les domaines de l’optimisation combinatoire et de l’apprentissage machine. Alors que les technologies de calcul quantique sont en devenir et que celles du calcul classique progressent toujours, cette recherche cherche  caractériser les capacités calculatoires des diff rents processeurs quantiques (D-Wave, NISQ et futures machines LSQ) afin de montrer dans quel cadre on peut en espérer une utilisation concrète.

Equipes de recherche

LIX/Grace

Activités de recherche

Factorisation quantique

La nature m me de l'ordinateur quantique permet de concevoir des algorithmes fondamentalement diff rents pour factoriser des nombres entiers, comme montré par Shor. Cet algorithme est cependant encore très théorique. En réalité, il peut être amélioré par la théorie algorithmique des nombres avant d' être réalisé en matériel, comme montré par Morain et Smith en 2018. De mani re curieuse, ce sont les nombres les plus difficiles  factoriser en classique qui deviennent les plus faciles  factoriser en quantique. Ces travaux vont être prolongés.

Cryptographie post-quantique

L'arrivée possible de l'ordinateur quantique compromet la sécurité des algorithmes cryptographiques les plus couramment utilisés, base de théorie des nombres. La communauté  cryptographique internationale a donc développé un nouvel axe de recherche, pour concevoir des algorithmes résistants à l'ordinateur quantique. Alain Couvreur, Ben Smith, Thomas D bris, de l'équipe de cryptographie du LIX (Grace) travaille activement dans ce domaine, pour proposer des algorithmes de chiffrement et de signature.

Codes quantiques

Un des problèmes majeurs pour la réalisation de l’ordinateur quantique est celui de la stabilité des qbits, qui stockent de mani re quantique l’information manipulée. Le ph nom ne de décohérence peut détruire cette information. Une solution est l’utilisation de codes correcteurs quantiques, qui permet de remettre des registres dans leur tat avant perturbation, en corrigeant les erreurs produites par l’environnement. Ces codes ont été utilisés en pratique dans les grandes annonces de record de nombre de qbits. Alain Couvreur de l’équipe de Cryptographie du LIX (Grace) travaille sur ces sujets.

Laboratoire Léon Brillouin

Equipes de recherche

• LLB/NFMQ

Activités de recherche

Magnétisme frustré

Structure magnétique locale dans une glace de spin. Les spins sont situés sur un réseau pyrochlore, formé de tétraèdres joints par leurs sommets. Chaque tétraèdre possède 2 spins « in » et 2 « out », une règle qui s’apparente à la condition de divergence nulle d’un champ magnétique émergent. Le champ électrique dual habite le réseau pyrochlore dual, ici en bleu.

Les dernières décennies de recherche en mati re condensée ont vu l'émergence d'une physique nouvelle, dépassant le paradigme de N el et transcendant les descriptions conventionnelles bas es sur la théorie de Landau. Le magnétisme frustré a contribué  à ces développements, en pointant l’existence de nouveaux tat de la mati re, par exemple de type  liquide de spin . L'intérêt pour ces tats provient de l’existence d’excitations fractionnaires, de champs de jauge émergents et de la propriété d’intrication quantique grande échelle. Dans ce cadre, nous nous intéressons aux systèmes de chaines de spins, aux réseaux Kagomés, pyrochlores et hyperkagomés. En variant le spin des éléments magnétiques, nous étudions la structure et la dynamique des configurations magnétiques par diffusion de neutrons.

Boucles de courants dans les oxydes corrélés

Modèle microscopique des boucles de courants : un nouvel état quantique se développe via une cohérence de la phase de l’orbitale 3d du cuivre avec celles des orbitales p de l’oxygène, formant deux boucles de courant de sens opposé. Ces boucles fermées créent des moments magnétiques orbitaux observés par diffraction de neutrons.

Des phénomènes émergents apparaissent dans les supraconducteurs non conventionnels (cuprates) ou les isolant de Mott en présence d’un fort couplage spin- orbite (iridates). Ces composés sont caractérisés par un ordre antiferromagnétique à longue portée à dopage nul qui est détruit en dopant ces matériaux. Ils développent alors des états exotiques de type métal étrange, avec des phases de pseudogap et même de la supraconductivité à haute température critique. Dans les deux exemples, ces matériaux possèdent des ordres cachés, qui semblent être liés à la présence de boucles de courants, tournant en sens opposés (voir figure). Ces boucles résultent de fortes corrélations électroniques entre les orbitales du cuivre ou iridium avec le ligand oxygène et peuvent alors
être associées à des moments toroïdaux.

Skyrmions et textures magnétiques

Les défauts topologiques sont au cœur de la recherche contemporaine en matière condensée, à l'interface entre physique fondamentale et applications technologiques. Qu'il s'agisse de skyrmions, de points de Bloch ou de fermions de Weyl, ces objets confèrent des propriétés remarquables aux matériaux qui les accueillent. Nous nous intéressons aux systèmes ayant tendance à former des structures magnétiques favorables à l'apparition de tels défauts. En utilisant des paramètres d'ajustement tels que le désordre chimique ou la pression, nous étudions la morphologie et la dynamique des textures magnétiques présentes au sein des matériaux. La diffusion et la spectroscopie de faisceaux quantiques (neutrons, rayons X et muons) nous permettent de sonder ces propriétés sur plusieurs échelles de temps et d'espace.

Equipes de recherche

• LMCE/Q

Activités de recherche 

Apport des technologies quantiques aux caractérisations de matériaux soumis à des conditions extrêmes.

Travaux en collaboration avec Jean-Fran ois Roch (LAC, ENS Paris-Saclay) : Nouveaux diagnostics pour les expériences haute-pression réalisées en cellule enclume diamant. Des centres NV du diamant implantés directement dans les enclumes en diamant permettent de mesurer les propriétés magnétiques des matériaux à haute pression.

Contribution of quantic technologies to characterization of materials under extreme pressures: use of diamond NV centers to measure the magnetic properties of materials in Diamond Anvil Cells

Recherche de cas d’usage pour les ordinateurs quantiques

Thématiques étudiées: science des matériaux, physique nucléaire, algorithmes d’apprentissage automatique

Research of use cases for quantum computing in material sciences, nuclear physics and machine learning

Equipes de recherche

• QuaCS (Quantum Computation Structures)

Activités de recherche

Quantum Cellular Automata as

• a mathematical theory
• an architecture
• quantum simulation framework

ZX-calculus

• a complete graphical model of quantum computing
• for optimization
• for verification

Quantum programming languages

• Circuits synthesis
• Formal proofs of algorithms
• Resource estimation

Laboratoire de Mathématiques de Versailles

Equipes de recherche

• LMV/CSI Cryptologie et sécurité de l’information

Activités de recherche 

Algorithmes post-quantiques en cryptographie

L'équipe crypto du LMV a conçu plusieurs algorithmes post-quantiques en cryptographie asymétrique, à base soit d’isogénies sur les courbes elliptiques (avec des propriétés intéressantes, du fait de la difficulté supposée exponentielle du problème algorithmique sous-jacent et de la petite taille des clés), soit de polynômes multivariés (avec notamment des signatures remarquablement courtes). Dans ce cadre, nous avons par ailleurs coordonné les soumissions à l'appel international du NIST (National Institute of Standards and Technology, USA), dans le cadre du projet PIA3 RISQ (Regroupement de l'Industrie française pour la Sécurité Post– Quantique http://risq.fr/) : parmi les 25 algorithmes sélectionnés pour la 2ème phase au niveau mondial, 6 sont issus de RISQ, dont 2 de l'équipe.

Laboratoire national de métrologie et d’essais

Equipes de recherche

• LNE/MEFQ Métrologie électrique fondamentale et quantique

Activités de recherche

Etalons électriques quantiques et instrumentation associée pour le SI

Cette activité concerne l’ingénierie des étalons à effet Hall quantique(EHQ) et à effet Josephson, pour la dissémination des unités de mesure électriques du système international d’unités SI : A, V, F,… . Elle comprend aussi le développement de l’instrumentation nécessaire à l’utilisation de ces étalons au meilleur niveau d’exactitude (e.g. comparateur de courants à SQUID).
Les challenges actuels pour ces dispositifs sont l’extension des applications, la simplification de l’utilisation, la miniaturisation, l’intégration jusque dans des systèmes complexes, en conservant fiabilité et exactitude. Les développements peuvent viser des TRL élevés.

Parmi les travaux en cours : la fiabilisation de l’étalon de résistance à EHQ dans le graphène pour un fonctionnement simplifié, à qq teslas, dans un réfrigérateur compact en cycle fermé, la réalisation d’un étalon de courant par combinaison des étalons à EHQ, à effet Josephson et d’un comparateur de courants à SQUID. La perspective emblématique est celle d’un multimètre quantique.

Réseaux de barres de Hall lithographiées dans des hétérostructures GaAs/AlGaAs (OMMIC) pour la réalisation de l’étalon de résistance à effet Hall quantique avec des valeurs ajustées entre 100  et 1,29 M 
 

Matériaux et phénomènes quantiques pour la métrologie électrique quantique avancée

Cette activité regroupe les travaux de recherche exploratoires, à bas TRL, sur des matériaux et des phénomènes quantiques, pour des applications en métrologie quantique, au-delà de l’état de l’art. Il s’agit de développer des étalons du SI, mais aussi d’établir des expériences ou des méthodes de référence, parfois au-delà du SI, ainsi que de développer des capteurs. Ces travaux de recherche peuvent être assez fondamentaux avec une contribution à la connaissance.

Parmi ces travaux : tests d’universalité de l’effet Hall quantique (EHQ), transport d’électrons uniques, détecteur d’électrons uniques fondé sur la rupture de l’EHQ dans le graphène pour des expériences d’interférométrie, mesures de bruit en régime EHQ, hétérostructures de van der Waals à base de graphène et de h-BN.
En perspective : EHQ en régime AC, effet Hall quantique anormal (QAH), hétérostructures de van der Waals de matériaux 2D avec contrôle de l’angle d’alignement (twistronics), 2D COF-MOF, et autres matériaux de Dirac…

Col 3 content area

Laboratoire d’Optique Appliquée

Equipes de recherche

• LOA/APPLI

Activités de recherche

Electron-phonon coupling in colloidal quantum dots

In this project we explore the infrared response of self-doped colloidal nanocrystals (in particular HgSe, HgTe and one Ag2Se). Femtosecond infrared spectroscopy and time-resolved electron diffraction are used to follow in real-time both electrons and phonons dynamics. As we are able to excite coherently a specific phonon mode, we are able to investigate the electron-phonon coupling in a selective way. Such a coupling is expected to be strongly modified by the electrons and phonons confinement in the quantum dots. This investigation will generate a detailed insight into the relaxation mechanisms of confined carriers. Fundamental processes ruling the electronic structure and dynamics will be identified and quantified to envision the use of self-doped nanocrystals in emerging infrared nanocrystal optoelectronics.

Figure 1 : Infrared spectra for two sizes of HgSe nanocrystals.

Realization of a tunable nanometric terahertz oscillator based on two-dimensional materials

The main objective here is to realize a tunable terahertz oscillator at the nanoscale. This can be done using collective interfoliar movements in two- dimensional crystal structures. Taking the example of graphene, by applying an electric potential difference between two layers of graphene, it is possible to create an oscillating dipole at the frequencies of the two interlayer vibrational modes, about 1 THz for the shear mode and about 4 THz for the breathing mode. We have already shown our ability in controlling the shearing mode in a bilayer graphene, which must now be further investigated under an external electric bias. This concept can be used with any two-dimensional material, and pave the way toward the realization of a terahertz nano antenna.

Figure 2 : (a) Real-time measurements of shearing mode oscillations in few-layer graphene by time-resolved spectroscopy and (b) schematic representations of the corresponding vibrations.

Ultrafast dynamics in strongly correlated materials and topological insulators

In strongly-correlated electrons materials the interplay within all the degrees of freedom of the crystal, like electrons and phonons, produces peculiar phases such as charge density waves and high temperature superconductivity, as well as a a competition between the metallic and the insulating state that can be controlled by a laser pulse. This leads to interesting fundamental questions about the different ways to control and to address these states on demand by external stimuli. In this trend, we investigate the mechanisms behind ultrafast photoswitching between the metallic and the insulating phases in two classes of quantum materials: strongly correlated materials and topological insulators. This opens the way to realize optical-based ultrafast transistors.

Figure 3 : Investigation of the ultrafast photoinduced metallic state in V2O3 crystal. (a) Measurement of the coherent A1g optical phonon mode by transient reflectivity measurement in the metallic phase (PM) and insulating phase (PI). (b) and (c) Comparison of the Fourier transform of the signals with a standard Raman measurement, pointing out a phonon hardening that manifests the non-thermal character of the photoinduced state.

Equipes de recherche

• LPS/MATRIX – Matière et Rayonnement

Activités de recherche

Multiferroicity

Our team is interested in bulk quantum materials presenting astonishing properties. At the origin of these remarkable quantum properties are the couplings between charge, spin and lattice degrees of freedom (multiferroicity). These properties can be manipulated with external parameters such as pressure, temperature, electric or magnetic field.
Our activity focuses on the description of the microscopic mechanism coupling these different degrees of freedom at different time scale (static and dynamic). This opens the way to new applications in the field of spintronics, magnonics and quantum-scale information storage and manipulation.

3D plot of the diffracted peak in reciprocal space, revealing the symmetry breaking at the origin of ferroelectricity in TbMn₂O₅

Exotic magnetism and superconductivity

Unconventional superconductors generally occur near an exotic magnetic phase. These generally mysterious phases (such as the pseudogap phase of cuprates) consist of new quantum magnetic states (spin or orbital). We are interested in characterizing and defining these new quantum objects in these bulk materials and thus determine their role in the appearance of superconductivity.

Atomic and magnetic structure of multiferroic and superconducting iron based spin ladder compound BaFe2Se3.

• LPS/TQM Theoretical Quantum Matter

Activités de recherche

Unconventional and topological superconductivity

The quest for unconventional high-Tc superconductivity is one of the most outstanding research fields in our group. Besides the long-sought cuprate oxides, in recent time our attention has also turned to iridium oxides, which are widely studied by the experimental groups at the LPS. These systems are believed to posses the ingredients to produce a high Tc superconducting mechanism and present novel topological strong spin-orbit interaction. This is also the case in systems where magnetic impurities are embedded in a conventional superconductor, which can give rise to an anomalous superconducting states, displaying unconventional p-wave pairing and topological edge states. This challenging problems are also studied within ad hoc theoretical methods (such as DMFT), developed within our group.

Fig.: Magnetisation-induced topological Majorana states in superconducting materials.

Graphene, relativistic and topological matter

The theoretical study of graphene and other relativistic matter is one of the group's vastest research fields.
Graphene is investigated, but recently the focus has shifted to materials beyond graphene, such as organic crystals that depict tilted Dirac cones. Relativistic aspects also govern the electronic properties of Weyl semimetals, the three-dimensional analogue of graphene. Another class of Dirac materials is that of transition-metal dichalcogenides, direct-gap semiconductors whose electronic properties are most likely described in terms of massive Dirac fermions. A particular field of interest is the interplay between crystal defects and the electronic properties in Dirac and topological matter, e.g. impurity states and anisotropic Friedel oscillations in graphene-like structures.

Quantum transport in correlated nanostructures

Electronic and spin transport is strongly affected by quantum effects in low-dimensional nanostructures, such as quantum dots, nanowires and hybrid circuits. The theoretical understanding of this quantum transport is therefore fundamental for the characterisation and fabrication of next- generation electronic nano-devices, e.g. in the framework of quantum computation or simulation. The understanding of these phenomena is at the heart of the group’s activity, namely in non- equilibrium quantum and diffusive transport, quantum noise.
Furthermore, quantum light-matter coupling (quantum electro- dynamics) in hybrid circuits and quantum cavities is strongly investigated.

Fig. : Resonant mode of a half- wavelength coplanar cavity, with a quantum point contact (QPC) which contacts the centre strip and lower ground plane. A dc voltage is also applied to the junction via the centre strip at a voltage node, so as not to induce losses. The state of the resonant microwave mode provides a quantum ac voltage across the junction. We are interested in how transport in the QPC acts as a non-trivial probe of prepared quantum microwave states of the cavity such as squeezed or Fock states.

• PULS – Phénomènes ultrarapides lumière-solides

Activités de recherche

Dynamique électronique dans les matériaux quantiques

L’activité de l’équipe PULS est centrée sur le développement de nouvelles méthodes spectroscopiques ultrarapides pour l'étude des matériaux quantiques. Le projet de recherche est basé sur l’utilisation de la spectroscopie ARPES résolue en temps, et d’autres techniques qui donnent accès à la structure électronique des matériaux hors équilibre. Ces techniques sont en fort développement grâce au progrès continu des sources laser ultra-brèves, et donnent accès à des phénomènes et à des paramètres physiques importants et relativement peu explorés, tels que les transitions de phase photo-induites, la durée de vie des états excités, le couplage électron- phonon, etc.

Dynamique ultra-rapide des bandes électroniques dans un isolant topologique

• STEM – Microscopie électronique

Activités de recherche

Imagerie d’émetteurs quantiques

Nous utilisons des techniques de spectromicroscopies à base d’électrons libres dans des microscopes électroniques à transmission, pour déterminer, ultimement à l’échelle atomique, la structure et les propriétés optiques d’émetteurs quantiques. Les émetteurs d’intérêt vont de puits quantiques de nitrure d’éléments III à des défauts ponctuels dans les matériaux de van der Walls. Les spectroscopies utilisées sont essentiellement la spectroscopie de perte d’énergie électronique et la cathodoluminescence.

Cartographie de cathodoluminescence révélant l’émission d’un défaut ponctuel dans le nitrure de Bore hexagonal émettant dans l’UV (gauche) et se comportant comme un émetteur de phonons uniques (droite)

Physique des spin-vallées dans les TMDs

Les propriétés optiques des monocouches de dichalcogénures de métaux de transition (TMD) et de leurs bicouches et hétérostructures sont intimement liées à leur structure. Ainsi, les monocouches possèdent un gap direct et des propriétés de forte luminescence associées, ainsi que qu'une structure de bande particulière permettant d'étudier la physique des spin-vallées aux points K non-équivalents. Dans les bicouches et hétérostructures, la formation de motifs moirés avec des périodicités à l'échelle nanométrique entraîne des changements drastiques de leur structure électronique et, par conséquent, de leur réponse optique.
Notre équipe se spécialise dans l'étude des spectres d'émission et d'absorption des monocouches et des bicouches de TMD avec une résolution nanométrique, que nous relions aux informations chimiques et structurelles à l'échelle nanométrique, voire atomique.

a) Image à résolution atomique d'une fissure sur une monocouche de WS2 (les points brillants sont des atomes de tungstène). b) Émission (cathodoluminescence, CL-pourpre) et absorption (spectroscopie de perte d'énergie d'électrons, EELS-orange) d'une monocouche WS₂. Les réactions excitoniques sont marquées par Xi (i=A, B, C). X- correspond à l'émission de trions.

Degrés de liberté dans les nanostructures d'oxydes corrélés

Parmi les matériaux quantiques, les oxydes de métaux de transition présentent des propriétés inédites dues aux fortes interactions entre électrons et degrés de liberté de charge, de réseau, de spin et orbitaux. Nous utilisons les techniques de microscopie et spectroscopie électroniques pour étudier comment ces degrés de liberté évoluent dans des couches minces, des hétéro-structures et à leurs interfaces.
L’intérêt de ces techniques est notamment de pouvoir étudier des inhomogénéités (par exemple de charge et de réseau) à l’échelle nanométrique.

Imagerie de type STEM-ABF démontrant la suppression uniaxiale de distorsions antiferrodistortives pour des super-réseaux ultraminces à base de manganites. Ces modifications modifient drastiquement les propriétés magnétiques du système.

• LA PHYSIQUE AUTREMENT

Activités de recherche

Nous explorons de nouvelles façons de vulgariser et d’enseigner la physique, en particulier dans le champ de la quantique.
Nous développons pour cela des collaborations avec des designers, créatifs, vidéastes et illustrateurs. Nos productions sont ensuite testées dans différents cadres puis diffusées gratuitement. Nous menons également des recherches en lien avec les SHS sur ces nouvelles formes de médiation et d’enseignement.
A titre d’exemple, dans le champ de la quantique, nous créons :

• des animations pédagogiques sur différents concepts de base ou recherches récentes
• des illustrations et BD illustrant les idées ou courbes clé ou la vie des labos, par exemple ces paysages quantiques
• des vidéos décrivant des champs scientifiques, par exemple la topologie quantique
• des dispositifs ou des expériences permettant de mettre en scène des phénomènes quantiques, comme ces manivelles pour expliquer l’ordinateur quantique
• des conférences grand public dans différents contextes, confinés ou non.

 Une de nos animations 3D illustrant les concepts de la quantique :

• HP - Corrélations électroniques et Hautes Pressions

Activités de recherche

Photonique quantique

La photonique suscite beaucoup d'intérêt aussi bien sur le plan fondamental qu'appliqué. Nous nous intéressons aux structures de graphènes photoniques métalliques : la formation et les propriétés des cônes de Dirac, ainsi les modes de propagation des ondes de lumière associés aux différentes parties de ces cônes, pouvant trouver l’application en vallée-photonique. Nos intérêts portent également sur d’autres structures photoniques, tels que la formation des bandes basses fréquences en relation avec les modes de résonance locaux dans les structures métalliques, ainsi que la formation des gaps photoniques, le régime de la localisation intrinsèque de la lumière et sa limite, ainsi que l’effet de délocalisation par désordres dans les structures quasipériodiques.

Propagation inhabituelle d’un faisceau électromagnétique, associée à la partie inférieure (a) et supérieure (b) des cônes de Dirac pour deux vallées différentes K et K’, dans une structure de graphène photonique métallique triangulaire. Les graphiques insérés en bas présentent les directions de propagation attendues.

Transition de Mott et supraconductivité dans les AxC60

La supraconductivité (SC) au voisinage des phases magnétiques est un sujet activement étudié aujourd’hui, et le rôle des fluctuations du spin dans la formation de l'état supraconducteur ainsi que la symétrie de son paramètre d'ordre sont très débattus. En ce qui concerne les fullerènes A₃C₆₀ dopés aux alcalins, une famille distincte des supraconducteurs à haute température de transition, la phase SC observée en onde s a longtemps été interprétée comme une supraconductivité de type purement BCS, pilotée par des phonons localisés, avec une faible incidence des corrélations électroniques. Un intérêt renouvelé se manifeste car dans une structure cubique A15 de Cs₃C₆₀, une transition des phases antiferromagnétiques vers la SC est observée sous pression. Nous étudions ces phases par RMN et muSR sous pression pour élucider le mécanisme à l’origine de la supraconductivité dans ces matériaux.

Diagramme de phases (Température, Pression) du composé Cs₃C₆₀

Physique au voisinage des points critiques quantiques

En jouant sur un paramètre tel que la pression ou le dopage, les états fondamentaux quantiques (antiferromagnétisme, onde de densité,…) peuvent être déstabilisés à température nulle lorsque le paramètre atteint une valeur critique pc. Au-delà de p_c, l’état métallique est de nouveau stabilisé et la supraconductivité peut même apparaître. Au voisinage de p_c, l’état normal ne suit pas forcément les lois physiques attendues. Par exemple, la résistivité ne suit pas forcément une loi en T² attendue pour un liquide de Fermi. Nous étudions ce comportement en fonction de la pression hydrostatique ou de la pression uniaxiale pour différents composés à fortes corrélations électroniques.

Résistivité linéaire (à basse température et fort champ magnétique) et résistivité quadratique (à haute température) dans un composé moléculaire quasi- bidimensionnel.

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Laboratoire de physique theorique et modeles statistiques

Equipes de recherche

• LPTMS/MCSQ matière condensée et systèmes quantiques

Activités de recherche

Analogous Hawking radiation

Confronting the predictions of general relativity and quantum mechanics, Hawking showed in 1973 that black holes are not completely black, but emit a faint radiation of quantum origin. However, this radiation is too weak to be detected in the astrophysical context. We can circumvent this difficulty because we are now able to realize analogous systems in the lab: the flow of some quantum fluids emit a sonic analogue of the Hawking radiation. In a series of works, members of the lab theoretically analyzed some experimental platforms making it possible to realize an analogous black hole in a Bose-Einstein condensate.
Although they widely differ in intensity and wavelength, the light emitted by a usual star and the Hawking radiation of a gravitational black hole have an important feature in common: their spectra are both fixed by their surface temperature and obey the so-called Planck’s law. In a recent work, Mathieu Isoard and Nicolas Pavloff theoretically reproduced recent experimental results and challenged their interpretation by arguing that, at variance with what occurs in a gravitational black hole, the analogous radiation of a Bose-Einstein condensate is not planckian.

Chaos assisted tunneling with cold atoms

The field of quantum simulation, which aims at using a tunable quantum system to simulate another, has been developing fast in the past years as an alternative to the all-purpose quantum computer. In particular, the use of temporal driving has attracted a huge interest recently as it was shown that certain fast drivings can create new topological effects, while a strong driving leads to e.g. Anderson localization physics. We investigate a quantum chaos transport mechanism called chaos-assisted tunneling which provides new possibilities of control for quantum simulation. Indeed, this regime generates a rich classical phase space where stable trajectories form islands surrounded by a large sea of unstable chaotic orbits. This mimics an effective superlattice for the quantum states localized in the regular islands, with new controllable tunneling properties. Besides the standard textbook tunneling through a potential barrier, chaos-assisted tunneling corresponds to a much richer tunneling process where the coupling between quantum states located in neighboring regular islands is mediated by other states spread over the chaotic sea. This process induces sharp resonances where the tunneling rate varies by orders of magnitude over a short range of parameters. Such systems can be used to enlarge the scope of quantum simulations in order to experimentally realize long-range models of condensed matter.

Phase-space picture of a chaotic kicked rotator. A wave-function initially localized (right red dot) tunnels through the chaotic sea to left regular island.

Laboratoire des Solides Irradiés

Equipes de recherche

• LSI/ST SPECTROSCOPIE THEORIQUE

Activités de recherche
 

Description théorique des excitations électroniques par la lumière

Théorie fondamentale, dérivation d’approximations, développement d’algorithmes et de codes de calcul, applications (prédictions, collaboration avec des expériences, ponctuellement avec l’industrie) pour la description des excitations électroniques par la lumière : processus linéaires, non-linéaires et plasmonique

Chlorure d’argent : effet d’une résonance excitonique sur la densité induite en réponse à une perturbation localisée (Thèse A. Lorin)

Description théorique du couplage électron-boson et boson-boson

Théorie fondamentale, dérivation d’approximations, développement d’algorithmes et de codes de calcul, applications (prédictions, collaboration avec des expériences, ponctuellement avec l’industrie) pour la description du couplages électron- boson et boson-boson : dérivation de premiers principes, étude des conséquences du couplage

Angle-resolved photoemission spectra in bulk aluminum: Band structure and satellites due to plasmons coupled to the quasi-particles. Left: theory, intrinsic only, Middle: experiment, Right: theory including extrinsic, interference and temperature effects.
Zhou et al., Proceedings of the National Academy of Sciences 117 (46), 28596-28602 (2020)

Processus quantiques dans les systèmes à basse dimension

Théorie fondamentale, dérivation d’approximations, développement d’algorithmes et de codes de calcul, applications (prédictions, collaboration avec des expériences, ponctuellement avec l’industrie) pour l’étude des processus quantiques dans les systèmes à basse dimension

Electronic distribution of the wave function of the lowest-energy exciton of graphane and h-BN for the fixed position of the hole (black sphere) calculated for q → 0 (left) and 0.4 Å⁻¹ (right). The black arrow is the direction of q ≠ 0. White and green spheres represent N and B atoms in h-BN and H and C atoms in graphene.
Cudazzo et al., PRL 116, 066803 (2016)

• LSI/NEE NOUVEAUX ETATS ELECTRONIQUES

Activités de recherche

Dynamique ultra-rapide des matériaux quantiques

L'interaction de photons avec la matière condensée est un des plus vieux et des plus vastes domaines de la physique. La plupart de ces expériences sont traditionnellement réalisées à l'équilibre et permettent d'explorer l'état fondamental des matériaux. Néanmoins, de nouveaux horizons apparaissent lorsque l'on considère les états hors équilibre de la matière condensée : on peut alors avoir accès aux états excités de la matière et à la façon dont ils relaxent vers l'équilibre. Cet aspect dynamique offre de nouvelles informations sur les couplages électron-électron ou électron-phonon. On peut aussi envisager d'utiliser la lumière laser pour induire, voire contrôler propriétés topologiques, supraconductivité et de spin. Nous utilisons plusieurs techniques de spectroscopie ultrarapide pour explorer ce sujet.

• LSI/QCMX Quantum Circuits and Matter Lab (QCMX)

Activités de recherche

Circuits et matière quantiques

Notre    but    est    d'explorer    les    propriétés quantiques des circuits électroniques et de la matière. La stratégie consiste à coupler des circuits supraconducteurs habituellement utilisés pour traiter  l'information  quantique à des matériaux afin de sonder leurs propriétés quantiques et découvrir de nouveaux états électroniques de la matière. Ceci pourrait permettre d'identifier de nouveaux porteurs d'information quantique et de simuler des problèmes quantiques complexes à plusieurs corps.

Circuit Josephson composé d’un nanotube de carbone et d’électrode supraconductrice (gauche). Diagramme illustrant le couplage d’une telle jonction avec une cavité dans le but d’effectuer le contrôle cohérent de ses niveaux quantiques (à droite).

• LSI/PCNANO Physics and Chemistry of Nanoobjects (PCnano)

Activités de recherche

Spintronics, nanomagnetism
Theory / modeling: thermokinetic approaches to transport, magnetization dynamics, spin-dependent and chiral tunneling effect, spin lasers
Experimental activities: transport measurements under magnetic field, thermal phenomena, spin injection in ferromagnetic / semiconductor metal structures, ferromagnetic nanowires, piezoelectricity and magnetostrictive properties.

• LSI/TSM THÉORIE DE LA SCIENCE DES MATÉRIAUX

Activités de recherche

Modélisation des états excités de défauts dans les solides

Development of quantum-scale methods for condensed matter and numerical simulations in high-performance computing (HPC) environments
Modeling of the behavior under pressure of N-body states of point  defects  such as  the nitrogen-vacancy center in diamond, in connection with the development of quantum sensors in a diamond anvil press carried out in teams of the DIM Major Interest Area SIRTEQ. Study of defects in solids rich in boron: boron, boron carbides.

Nitrogen-vacancy center in the diamond: atomic structure (left), electronic (center) and probabilities of electronic presence (right).

Laboratoire de Traitement et Communication de l’Information

Equipes de recherche

• LTCI/IRQ Informatique et Réseaux Quantiques

Activités de recherche

Information Quantique et Cryptographie

(PI : Romain Alléaume)

Ces activités à dominante théorique visent à explorer les liens entre cryptographie, sécurité des infrastructures et information quantique, à travers plusieurs axes.
1)    Cryptographie quantique théorique. Nous étudions la construction de nouveaux protocoles dans un modèle de sécurité hybride (cf figure) . Nous développons également des constructions permettant d’opérer la CV-QKD de façon indétectable (covert).

2)    Sécurité Hardware : nous étudions, expérimentalement et théoriquement comment améliorer la sécurité des implémentations en cryptographie quantique, notamment CV- QKD. Nous participons à l’écriture du premier Protection Profile pour la QKD au sein du projet européen OpenQKD et dans le cadre de l’ETSI QKD ISG dont nous sommes partenaire fondateur.

Principe de la construction « Quantum- Computational Timelock ». On suppose (modèle QCH) qu’un attaquant a une mémoire quantique dont la durée de vie tcoh est inférieure à la durée nécessaire tcomp pour casser le chiffrement computationel (Enc).

Quantum Machine Learning

(PI : Filippo Miatto)

Quantum Machine Learning (QML) is the intersection between quantum information and classical Machine Learning. In QML there are two complementary approaches: develop ML algorithms that run on quantum hardware, or
use ML algorithms to aid the development of quantum devices. Our research aligns with the second approach. Specifically, we develop gradient-based optimization methods to design quantum photonic circuits like quantum repeaters, or for bosonic quantum error correction and cluster state generation. In our most recent work [1], we introduced an algorithm that is 100x faster at optimizing photonic circuits than the previous state of the art.
[1] “Fast optimization of parametrized quantum optical circuits” Filippo M. Miatto, Nicolás Quesada, arXiv:2004.11002 [quant- ph]

Quantum optical neural networks are Variational Quantum Circuits composed of alternating layers of Gaussian and non-Gaussian transformations, which can be trained to become virtually any device.

Post-Quantum Cryptography

(PI : Hieu Phan)

The security of most currently deployed public-key cryptosystems is based on the assumed hardness of mathematical problems that can be easily solved using Shor's algorithm on a sufficiently powerful quantum computer. The community is thus paying special attention to cryptosystems that are believed to remain secure even against quantum attacks. These systems are often based on other well-studied computational assumptions, including those from lattices and codes.
On the other hand, in many emerging applications of cryptography, the demand for security grows beyond the basic requirements. This requires us to consider advanced primitives against strong adversaries.
 

• LTCI/PIQ Physique et Ingénierie quantique

Activités de recherche

Optoélectronique avancée pour les communications optiques et les systèmes d’information quantique

(PI : Frédéric Grillot)

L’activité porte sur les émetteurs quantiques constitués d’hétérostructures semi-conductrices III-V de basse dimensionnalité. Dans ce cadre, nous étudions l’interaction lumière-matière d’une part dans les sources (interbandes) à ilots quantiques émettant à 1,3 et 1,55 microns, d’autre part dans les sources à cascade quantiques (intersoubandes) à 4 et 9 microns. Les objectifs sont 1) de développer des solutions photoniques pour les circuits quantiques intégrés sur silicium et 2) d’explorer de nouveaux paradigmes et concepts pour le hardware quantique aux grandes longueurs d’ondes. L’activité est sous- tendue par le déploiement de modélisations ad hoc (approches excitonique et multi-particulaires).

Gauche : boite quantique semi-conductrice émettant des photons indiscernables.
Droite : composant photonique a cascade quantique émettant une impulsion géante dans l’infrarouge moyen.

Systèmes de communication quantiques

(co-PIs : Yves Jaouen, Cédric Ware et Romain Alléaume)

Cette activité vise à développer systèmes et protocoles de communication quantique reposant pour partie sur des technologies photoniques largement déployées, notamment les systèmes modernes de communication cohérente. Il s’agit en particulier de mettre au point de nouveaux design permettant de co- déployer communications classiques et quantiques sur une même fibre et avec du hardware partagé, en mettant à profit les techniques de multiplexage, de contrôle du bruit, et traitement du signal (DSP), et de viser une intégration, à faible cout marginal, des communications quantiques (notamment CV-QKD) dans les infrastructures de communication optiques existantes. Cette activité est notamment liée au projet CIVIQ du QT
Flagship.

Plateforme expérimentale de communication cohérentes classiques à haut débit (jusqu’à 40 Gbit/s) sur laquelle on met au point la co-intégration de communications quantiques, reposant sur des récepteurs cohérents limités au bruit de photon.

Sources fibrées pour les communications quantiques

(PI : Isabelle Zaquine)

Etude théorique et expérimentale de nouvelles sources de paires de photons aux longueurs d’onde des télécommunications basées sur le mélange à 4 ondes dans des fibres à cristaux photoniques à coeur creux remplies de gaz rare sous pression. L’utilisation de ce type de gaz comme milieu non linéaire garantit l’absence de bruit d’origine Raman dans ces sources, contrairement à tous les autres types de sources fibrées.
Ces sources permettent de plus de modifier les corrélations spectrales entre les photons de la paire, suivant que l’on souhaite les utiliser comme sources de photons uniques annoncés ou de photons intriqués et sont accordables en longueur d’onde en variant la pression du gaz.

Valeur absolue de la différence de fréquence entre les photons de la paire et la pompe permettant de satisfaire la condition d’accord de phase en fonction de la longueur d’onde de pompe p. La valeur de  donnée par les couleurs est liée à la forme des corrélations spectrales des photons de la paire. En insert, la structure tubulaire de la fibre à cœur creux.

Equipes de recherche 

• LUMIN/NOOS Nano optique et spectroscopie (NOOS)

Activités de recherche

Nano-objects as quantum emitters

Chemical "bottom-up" methods allow the synthesis of nano-objects with perfectly controlled molecular structure. Thus, graphene quantum dots of graphene of predetermined shape and size can be synthesized, allowing in principle the engineering of their optical, electronic and magnetic properties. By studying these properties, our team aim the link between the chemical structure and the luminescence properties. Using this information, the nano-objects will be optimized for the targeted t application, such as a communication network node or sensor. We extend this approach to other nano-objects produced by bottom-up synthesis, carbonaceous or not.

Levitation of nanoparticles in vacuum

The observation of quantum effects at the scale of a mesoscopic particle is hampered by the dissipative coupling to the environment. The ability to "levitate" a nanoparticle in the vacuum using optical tweezers greatly reduces this coupling, opening the way to the observation of quantum effects at the scale of a macroscopic particle. Our team is working to increase the control exerted on levitating particles, either by tayloring the trapping optical potential, by controlling the environment, or by using artificial atoms hosted inside the nanoparticle such as NV centers in a nanodiamond.

• LUMIN/QP Quantum Photonics

Activités de recherche

Manipulation 3D de single photon source par des structures photoniques en polymère

Low one-photon absorption based direct laser writing (LOPA-DLW) has been demonstrated as an ideal method to create desired multi-dimensional submicrometric    polymeric/magnetic/plasmonic structures.
Recently, the LOPA-DLW was also demonstrated, via a double-step process, as an excellent way to optically address most kinds of nanoparticles (gold, quantum dot, KTP, etc.) and to precisely embed them into desired polymeric photonic structures. The coupling of a single quantum emitter (QD or NV) in a photonic structure allows controlling and optimizing its optical properties (brightness, spectrum, radiative lifetime). The photonic structures also allow control and manipulation of quantum light beam propagation in 3D space. This is an excellent base and very important for development of quantum
applications.

SEM and fluorescent images of SU8 photonic structures containing a single CdSe/CdS quantum dot. These coupled structures are realized by the LOPADLW method. The bright point located at the center of each structure represents the fluorescence of a single quantum emitter at ambient condition.

Quantum chaos and microlasers

We study microlasers as testbed systems for quantum chaos physics. Various two-dimensional resonator shapes are fabricated by e-beam lithography with a nanoscale quality, yielding to integrable, pseudo- integrable, or chaotic systems. Recently three- dimensional surface-like microlasers were obtained, like the Möbius strip microlaser on the figure, which opens the way to non-Euclidean photonics.

• LUMIN/LO – Lasers and Optics

Activités de recherche

Coherent processes in atom cells

This activity deals with the fine understanding of quantum phenomena occurring in three- and four-level atomic systems coupled with light, using mainly metastable helium cells, but also rubidium conventionnal and thin cells. This includes the application of these concepts to optical sensors or quantum information processing.

Quantum photonics

We develop phase sensitive amplifiers based on optical para- metric amplification in nonlinear optical fibers. The ultimate goal is to build noiseless amplifiers, with a quantum limited noise figure below 3 dB, for microwave photonics applications (distribution of RF local oscillators or radar signals, electronic warfare, radio over fiber, …).

Development of coherent sources

We develop optical parametric amplifiers for the generation of narrow linewidth tunable radiation in the visible and the infra- red and new lasers or optoelectronic oscillators for the generation of ultra-stable RF local oscillators. This research is trig- gered by applications in the domains of quantum information processing and remote sensing.

• LUMIN/DIADEMS Diamond-Enabled Materials and Sensors

Activités de recherche

NV-based quantum sensing

The DIADEMS team of LUMIN pioneered research on point defects in diamond more than 15 years ago, with the first realization of quantum cryptography testbeds and single- photon interference based on the luminescence of a single NV center. Enlarging these activities to NV spin physics, this background was applied to develop practical NV-based mag- netometers which allowed us to image magnetic nano- and micro-structures. We are currently implementing NV magne- tometry in diamond anvil cells to explore the magnetic and superconducting properties of materials under very high
pressure.

Detection of the Meissner effect using NV centers created on the culet of a diamond anvil.

Laboratoire de Physique de la Matière Condensée

Equipes de recherche

• PMC/EPS Electrons-Photons-Surfaces

Activités de recherche

Localization induced by alloy disorder in nitride compounds

We study localization effects induced by the intrinsic compositional disorder in nitride semiconductor alloys. The disorder results from the random positioning of the alloy atoms on the crystal lattice sites. As a consequence, the electronic potential exhibits strong fluctuations on the scale of a few nanometers. In this potential landscape, localization effects impact the electronic processes even at room temperature. In particular, photon emission from single localized states can be observed under local carrier injection. This opens a wide field for the study of quantum effects in disordered systems with the possibility of controlling the disorder by the alloy composition.

Photon emission from disorder- induced localized states in an InGaN/GaN quantum well measured by scanning tunneling electro- luminescence microscopy.

Exciton and spin dynamics in 2D semiconductor compounds

Novel 2D semiconductors made of single molecular sheet of transition metal dichalcogenide MX2 (such as M0S2, WSe2...) are promising building blocks for future opto-nano electronic quantum devices. We fabricate heterostructures of atomically thin compounds by using an all-dry mechanical exfoliation and assembling technique. Strong excitonic effects, which dominate the optical response of these materials, are present even at room temperature, and allow to explore a rich variety of physical phenomena related to many body interactions, spin-valleytronics and Berry curvature effects. In addition, other issues are emerging such as single photon emission from localized atomic defect states or from the effect of alloy disorder in ternary
compounds of the form MX2(x)Y2(1-x).

Exciton diffusion in hBN/WSe₂/hBN van der Waals heterostructure measured by photoluminescence
microscopy.

Defect-mediated charge and spin dynamics in semiconductors

Our work covers the effects of localized electronic states related to crystal defects on recombination and transport dynamics of non-equilibrium free charge in semiconductors where the defects are either intrinsically present or have been engineered. Charge trapping at atomic scale defects leads to a rich variety of opto- electronic phenomena such as single photon emission, spin- dependent effects... One example in dilute ternary nitrides is spin- dependent recombination (SDR) at Shockley-Read centres. SDR is fundamentally present in semiconductors, and can significantly increase the lifetimes and distances over which both charge and spin can be transported, even at room temperature.

Transport (red arrow) can be significantly affected by capture (orange arrow), emission and recombination (yellow arrows) on localized electronic states. Capture and emission rates can depend on experimentally accessible variables including spin and mechanical stress.

• PMC/ECM Electrochimie et couches minces

Activités de recherche

Influence of the surface chemistry and electric field on the magnetic properties of ultrathin ferromagnetic films

The team's magnetism activity is currently focused on the effect of a strong electric field on the nucleation and propagation of magnetic domains. The originality of our approach is to apply the electric field by putting the magnetic layer in direct contact with an electrolyte and to make the magnetic measurements in-situ. This configuration allows to apply large and spatially homogeneous fields. This work is carried out in collaboration with C2N.

Schematics of a magnetic domain in a ultrathin cobalt layer with a perpendicular magnetization.

• PMC/PI Physique de l’irrégularité

Activités de recherche

Localisation des ondes dans les milieux désordonnées

The "Physics of Irregularity" group of the PMC laboratory develops activities related to Quantum in the framework of the Simons project on wave localization. The general theoretical question is to understand how stationary states of waves remain confined to a small region of space due to static or dynamic disorder. This is closely related but goes beyond the well-known Anderson localization. The approach called the "localization landscape theory" gives access with a remarkable precision to the main properties of the quantum disordered system. This approach is developed in collaboration with numerous groups of mathematicians and theoreticians, and in close interaction with experimental teams working on localization effects in semiconductors and in cold atom systems.

Illustration of the “localization landscape theory” which allows to predict the geometry of eigen modes in a random potential.

• PMC/CS Chimie du solide

Activités de recherche

Rare-earth-doped nanoparticles for applications in quantum optics

We are interested in the synthesis and study of the physical properties of rare-earth-doped oxide nanoparticles, with the objective of optimally controlling the crystallinity, size and shape of the considered objects.
These particles exhibit remarkable polarized luminescence properties. We are studying the applications of these particles as luminescent probes. We are also developing ultra-high crystallinity systems for quantum optics in collaboration with the group of
P. Goldner at Chimie-ParisTech.

Nanoparticule de YVO4 :Eu de haute critallinité, image TEM et photographie avec et sans irradiation UV
 

Services répartis, Architectures, MOdélisation, Validation, Administration des Réseaux

Equipes de recherche

• SAMOVAR/JGA

Activités de recherche

Capacity Requirements of Quantum Repeaters

We consider the problem of path congestion avoidance in networks of quantum repeaters and terminals. In other words, the avoidance of situations when demands exceed capacity. We assume networks in which the sets of complete paths between terminals may affect the capacity of repeaters in the network. We compare the reduction of congestion avoidance of two representative path establishment algorithms: shortest-path establishment vs. layer-peeling path establishment. We observe that both strategies provide an equivalent entanglement rate, while the layer-peeling establishment algorithm considerably reduces the congestion in the network of repeaters. Repeaters in the inner layers get less congested and require a lower number of qubits, while providing a similar entanglement rate.

Entanglement swapping

Faking and Discriminating the Navigation Data of a Micro Aerial Vehicle Using Quantum Generative Adversarial Networks

We show that the Quantum Generative Adversarial Network (QGAN) paradigm can be employed by an adversary to learn generating data that deceives the monitoring of a Cyber-Physical System (CPS) and to perpetrate a covert attack. As a test case, the ideas are elaborated considering the navigation data of a Micro Aerial Vehicle (MAV). A concrete QGAN design is proposed to generate fake MAV navigation data. Initially, the adversary is entirely ignorant about the dynamics of the CPS, the strength of the approach from the point of view of the bad guy. A design is also proposed to discriminate between genuine and fake MAV navigation data. The designs combine classical optimization, qubit quantum computing and photonic quantum computing. Using the PennyLane software simulation, they are evaluated over a classical computing platform. We assess the learning time and accuracy of the navigation data generator and discriminator versus space complexity, i.e., the amount of quantum memory needed to solve the problem. The work received one of the Xanadu Research Awards.

Generator qubit circuit feeding the discriminator circuit (n is two)

Quantum Computing Assisted Medium Access Control for Multiple Client Station Networks

Introduction of a medium access control protocol based on quantum entanglement to avoid collisions. The scheme works for an arbitrary number of client stations, based on three strategies: qubit distribution, transmit first election and temporal ordering protocols. The first strategy leverages the concepts of Bell-EPR pair or W state triad. It works for networks of up to four client stations. With up to three stations, there is no probability of collision. In a four-station setup, there is a low probability of collision. The other two strategies, transmit first and temporal ordering work for a network with any number of stations. The transmit first strategy builds upon the concept of W state of size corresponding to the number of client stations. It is fair and collision free. The temporal ordering strategy employs the concepts of Lehmer codes and quantum oracles. It is collision free and achieves quasi-fairness.

Equipes de recherche 

• GALAXIES

Activités de recherche

Inelastic x-ray scattering (RIXS) in quantum materials

Electronic properties of bulk quantum materials
Valence transitions / magnetic collapse / superconductivity at extreme conditions
Low energy excitations / dispersion Correlated materials (3d, 5d) Heavy fermions (4f)    
 

High energy photoemission (HAXPES) in quantum materials    

Band structure and electronic proprités of quantum materials (surface / interfaces)
Charge transfert effect
Ultrafast electron delocalisation dynamics Oxide heterostructures
2D materials Multiferroics

• ANR HITS

Activités de recherche

Nanomatériaux et nanotechnomogies pour les produits du futur

Hybrid Interfaces for Tailoring of Spintronics (HITS)

ARPES and High energy photoemission (HAXPES) in quantum materials

The ultimate objective of the HITS project is to tailor the properties of spin injection at hybrid metal/molecule interfaces towards efficient molecular spintronics devices. This will be achieved thanks to the development of a full understanding and leveraging of the key uncharted states involved in molecular spin-valves: hybrid unoccupied electronic states at the interface.

• SEXTANTS

Activités de recherche

Etude de la densité electronique et de spin aux interfaces d’oxides complexes

Grâce à l’utilisation de la diffusion résonante des RX il est possible d’accéder à la densité électronique et à l’organisation des moment magnétiques (spins dans des oxides complexes. Une des forces de l’approche est la sélectivité chimique grâce à l’utilisation d’une longueur d’onde correspondant à un seuil d’absorption es RX.

Etude des excitations élémentaires dans les oxydes par diffusion inélastiques résonantes des rayons X (RIXS)

L’activité de recherche effectuée par diffusion résonante inélastique des rayons X (RIXS) porte sur l’étude des excitations électroniques et magnétiques. Le RIXS mesure l’énergie et la dispersion des excitations (champ cristallin, orbitalaire, magnétiques), le couplage électron-phonon dans les solides ainsi que la dynamique moléculaire dans les gaz. Avec le récent développement d’un environnement échantillon innovant « MAGELEC », pour l’application de champs électriques et magnétiques in situ, notre station expérimentale offre aujourd’hui une configuration unique au monde, ouvrant de nouvelles perspectives dans le domaine de la
spintronique et de l’optoélectronique.

• CASSIOPEE

Activités de recherche

Demi-métaux pour la spintronique    

Nous étudions par photoémission résolue en angle et en spin la structure électronique de composés de la famille des Heusler qui présentent la propriété d’être demi- métallique. Ces matériaux présentent un gap au niveau de Fermi dans les états de spin minoritaire et les états de conduction sont donc entièrement polarisés en spin.
Cette caractéristique en fait des matériaux particulièrement prometteurs pour être utilisés dans les jonctions tunnel magnétiques. D’une part, la polarisation totale des états de conduction permet d’envisager des magnétorésistances tunnel très élevées et, d’autre part, le très faible coefficient d’amortissement magnétique permet de réduire le courant nécessaire pour retourner l’aimantation par couple de transfert de spin dans des dispositifs MRAM (mémoire magnétique) par exemple.     
Densités d’états de spin majoritaire et minoritaire calculées (traits plein et pointillé respectivement) pour une série de composés Co2MnZ (d’après C. Guillemard, thèse de doctorat, Université de Lorraine).

Densités d’états de spin majoritaire et minoritaire calculées (traits plein et pointillé respectivement) pour une série de composés Co₂MnZ (d’après C. Guillemard, thèse de doctorat, Université de Lorraine).

Contrôle Ferroélectrique de l’effet Rashba dans les TMDCs

Nous étudions l’effet Rashba géant prédit à l’interface entre un dichalcogénure de métal de transition (TMDC) et un matériau ferroélectrique. En utilisant la spectroscopie de photoémission résolue en angle et en spin, nous caractérisons la structure de bande des TMDC déposés sur une couche mince ferroélectrique par épitaxie par jet moléculaire. Ceci permettra meilleure compréhension des TMDCs et de leur utilisation dans des dispositifs de spintronique. En étudiant des interfaces hybrides et des matériaux à fort couplage spin-orbite, cette activité s’inscrit dans le contexte des Matériaux Quantiques. Ce domaine d’étude est un formidable terrain de jeu pour dévoiler le rôle des symétries, de la topologie, des dimensions et des corrélations électroniques dans les propriétés macroscopiques des matériaux.    
 
 

Structure de bande de WS2 déposé sur du BaTiO3 ferroélectrique

Topological insulator for spintronics

New quantum states discovered in topological insulators (TI) has unveiled exciting opportunities in the field of spintronics. Their topologically protected conductive surface states with spin- momentum locked perpendicular to the momentum should provide a 100% charge to spin conversion (CSC) in spintronics devices via the Edelstein effect. Pure spin currents could also be converted into charge current (inverse Edelstein effect). In collaboration with other groups, we work on various TIs (Bi1-xSbx, Bi2(Se,Te)3 or α-Sn). To probe the CSC efficiency, we use an adjacent ferromagnetic material, both as a spin source or a spin sink and detector.    
 
 

Fermi surface of a TI, Bi₈₅Sb₁₅

• SixS

Organic molecules on metallic surfaces for microelectronics and spintronics applications

Intermetallics and surface alloys structures

Metallic nanoparticles for heterogeneous catalysis

Service de Physique de l’Etat Condensé

Equipes de recherche

• SPEC/Nano Groupe nanoélectronique

Activités de recherche

Electron quantum optics and heat quantum transport in graphene    

Under high magnetic field, the unique competition between the different symmetries of graphene and electronic correlations gives rise to a variety of exotic quantum states. The one dimensional quantum Hall edge channels associated with these states have very promising electronic coherence properties compared to conventional semiconductor two dimensional electron systems. This allows new electron quantum optics experiments where single electron excitations are guided along an edge channel in a manner akin to photons in an optical fiber. Furthermore, the strongly correlated nature of these quantum states give rise to chargeless bulk collective modes that reflect their spin and valley polarization, and that can lead to decoherence. To investigate those collective modes, we rely on electron interferometry as well as heat transport measurements.    
 

Optical Microscope image of a graphene electronic Mach Zehnder.

Quantum electrodynamics of electrical conductors

Owing to the probabilistic character of charge transfers in a quantum conductor, such as quantum point contacts or Josephson junctions, a dc bias produces quantum current fluctuations, which couple to the surrounding electromagnetic environment. We investigate the resulting dynamics in its many facets: The emitted RF radiation conveys information on charge transport mechanisms in ns timescales otherwise hardly accessible. Moreover, being emitted by a quantum source, the radiation displays quantum correlations as well. Not the least, the electrodynamic coupling can be engineered in order to provide a strong measurement back-action on the transport properties of the conductor itself, where the equivalent of the fine structure constant is of order 1, resulting in a regime unparalleled by other experimental platforms. Beyond aiming at providing a unified quantum description of electrical transport and electromagnetic radiation, this activity brings the opportunity to develop new quantum devices.    
 

A dc biased Josephson junction (inset) coupled to a high impedance RF resonant coil, a setup generating antibunched radiation (PRL 122, 186804 (2019)

Flying qubits

Our understanding of quantum mechanics has reached the level such that one exploits it for unprecedented applications. The most common approach, aimed at realizing qubits, manipulates discrete states based on localised two-level systems, often called: “artificial atoms”. Here, we explore continuous electronic states that propagate coherently in a solid-state device. They form flying qubits, where the information is encoded by the presence or absence of a single electron in a propagating quantum channel.
Paralleling photonic flying qubits, we are able to realize on- demand single electron source emitting “levitons” [Nature 2013]. Two-particle interference similar to Hong-Ou-Mandel interference are currently done as well as Electron Quantum State tomography [Nature 2014]. Using strong magnetic fields we can reach the fractional Quantum Hall regime showing anyonic excitations. On- demand time-resolved Single anyon sources are currently done [Science 2019]. Hong-Ou-Mandel anyon interference are in progress.

• SPEC/QUANTRONIQUE
   

Probing localized states at Josephson weak links    

Weak links between superconducting electrodes host discrete localized electronic states, called Andreev bound states (ABS). The ABS energies depend on the difference between the superconducting phases of the electrodes which is at the origin of a supercurrent through the weak link. We probe the spectrum of ABS in weak links made of semiconducting nanowires, and characterize their coherence with time domain experiments performed using circuit quantum electrodynamics techniques. Due to the spin-orbit interaction in the nanowire, ABS are spin- resolved, and microwave excitations allow manipulating the spin of a single quasiparticle.     

Nanowire weak link (green) in a superconducting loop (grey).
Microwaves induce transition between states with different spins.

Quantum Sensing and Computing with Spin-Superconducting Hybrid Devices

We develop hybrid quantum devices combining superconducting quantum circuits with spins in solids (NV centers in diamond, donors in silicon, rare-earth-doped crystals) at millikelvin temperatures, with applications in quantum sensing and quantum computing. In our devices the spins are located in close proximity to micron- or sub- micron scale resonators, thus reaching a large spin- microwave coupling. On the sensing side, we demonstrate new methodologies for magnetic resonance : ultra-sensitive spin detection, spin cooling. On the computing side, we use ensembles of electron spins with long coherence times (≈10ms - 1s) as multi-mode quantum memory for superconducting qubits.    

Superconducting resonator consisting of a capacitor in parallel with an inductor, deposited on top of a silicon substrate containing bismuth donor spins, biased by a magnetic field B₀

High impedance superconducting circuits
    

In quantum circuits, the ratio of the phase fluctuations to    circuits
dimensionless charge (# of Cooper pairs) fluctuations is equal to    the ratio of the circuit impedance to the impedance quantum    kΩ resistance.
RQ=h/4e²≃ 6.5 kΩ. In usual circuits this ratio is small and phase is    Center: a squid array
nearly a classical variable. In the recent years we learned how to    implementing a tunable
engineer Josephson junction (JJ) arrays or disordered    superinductor
superconducting nanowires to make reactive impedances that can    Bottom : resonator with a beat RQ. We also uncovered how charge fluctuators can affect such    disordered superconductor
“superinductors”. We furthermore recently clarified that JJs    nanowire superinductor
connected to resistances larger than RQ  remain perfectly  superconducting contrary to common belief.    

Such progress opens the way to realizing the quantum dual of e.g. the AC Josephson effect, implementing a coherent current source driven by a microwave signal.

High impedance quantum circuits

Top : a JJ in series with a 12 kΩ resistance. Center: a squid array implementing a tunable superinductor

Bottom : resonator with a disordered superconductor nanowire superinductor

• SPEC/LEPO Laboratoire d’Électronique et Nanophotonique Organique (LEPO)

Control of intersystem crossing in the emission of single photons by a plasmonic antenna

In the framework of the ANR JCJC PlasmonISC project (AAPG 2019), we are interested in the quantum properties of single molecules, that can be used as single photon sources. In particular, we are experimentally studying the possibility of controlling the exchanges between excited singlet (emitting) and triplet (non-emitting) states of a single fluorescent molecule under the influence of a plasmonic nano-antenna. The singulet-triplet transition rate, called inter- system crossing, is an important factor governing the emitted intensity, which must approach 100% for the realization of single photon sources.

Control of the emission of single photons by an individual molecule using a plasmonic antenna functionalized AFM tip

Anisotropic metamaterials with epsilon near-zero for quantum cascade infrared photodetection

In the framework of the ANR mEtaNiZo project (AAPG 2017), we are developing the use of electromagnetic modes propagating in a particular class of metamaterials with a dielectric constant close to zero ("epsilon-near-zero", ENZ) for quantum detectors of infrared photons. The combination of this lamellar and laterally surface structured material with a quantum cascade detector allows a strong field enhancement at the level of the photosensitive structure and thus a strong optimization of IR photons detection. In particular we use a quantum cascade detector structure as the heart of our devices, in a metal-insulator-metal resonator.

Schematic representation of the studied infrared photodetector combining a quantum cascade stacking forming an ENZ metamaterial and a lateral plasmonic structuring, the whole allowing the electromagnetic field enhancement.
 

• SPEC/LNO Equipe matériaux quantiques

Activité de Recherche

Quantum materials elaboration

The group is expert in the elaboration and exploration of the phase diagram of high Tc superconductors (HgBaCaCuO and BiSrCaCuO single crystals). Our studies are also devoted to the synthsis and investigation of new Mott insulators (iridates - single crystals and thin films, family of Fe- based spin scale type BaFe2Se3 - single crystals) together with Weyl semi-metals (kagame compounds Co3Sn2S2- single crystals).
Other aspects of our work also concern spin/charge conversion in topological insulating oxides and multiferroic interfaces.    

Single crystal and cristallographic structure of the HgBa2Ca2Cu3O8+d compound synthesised at the SPEC to study of the generic phase diagram of cuprates
 

Structures, Propriétés et Modélisation des Solides 

Equipes de recherche

• SPMS/SEMS STRUCTURES ELECTRONIQUES, MODELISATIONS ET SIMULATIONS

Activités de recherche

Defects quantum states for imagery and cryptography

Over the last 20 years or so we have been active in many aspects of what is now called Quantum Crystallography. More precisely, with the help of undergraduate, graduate phD students (De Bruyne, Y. Launay,,
B. Courcot, S. Ragot, C. Fluteaux, Z. Yan) or post-docs (I. Ciumacov, S. Gueddida) and through long standing collaborations (such as Faculté Pharmacie Paris-Saclay, Univ. Lorraine, Japan Synchotron Radiation Reasearch Institute) we have developed an expertise in the exploitation of the links between the quantum description of electrons in crystals and molecules and several high-resolution scattering methods. In the recent years we have focused our interests on the determination of the one-electron reduced density matrix (1-RDM) from a set of different experimental data provided by high-resolution X-ray diffraction (coherent elastic), convergent electron beam diffraction, and inelastic incoherent scattering (Compton scattering) of X-rays. Some of our works also tackled the spin density of electrons in molecular magnets for which we developed a model giving access to the spin resolved electron density in crystals by a joint use of high- resolution X-ray and polarized neutron diffractions. We have also proposed a procedure to reconstruct the unpaired-electron 1-RDM from polarized neutron diffraction and magnetic Compton scattering data.
Our recent efforts have mostly been in the improvement of strategies to enforce the N-representability condition of 1-RDM.
For the past 4 years (ending next Summer) J-M Gillet served as the chairman of the Quantum Crystallography commission of the International Union of Crystallography.     

Spin traced one-electron reduced density matrixin dry ice obtained from a set of X- ray diffraction structure factors and directional Compton profiles
De Bruyne & Gillet, Acta Cryst. (2020). A76, 1-6

Nuclear Quantum effects

We proposed in 2009 a universal quantum thermal bath to account for quantum statistics while using standard MD. The QTB-MD technique is an approximate approach that yields accurate results and save at least two orders of magnitude of computation time compared to the well-known PIMD method based on the path integral formalism of Feynmann. Over the past 5 years, we have improved the application of this method and combined it with the PIMD method to make it applicable for highly anharmonic systems. In collaboration with a team of the CEA/DAM, we have implemented the two methods, QTB- MD and QTB-PIMD, in the ABINIT band-structure computational code (see the corresponding form). These methods are also implemented since two years in the CP2K code by a former PhD of the laboratory, Fabien Brieuc, within the framework of his current post-doc.

Excited states in DFT

Starting in 2016, we have investigated the interplay between light and functional ferroic materials from ab-initio. In particular, the change of shape and symmetry at the atomic scale under illumination has prompted us to develop an original constrained DFT scheme to mimick the effect of thermalized photo-excited carriers. We have for example predicted a potential photo-induced phase transition between a polar and anti-polar state in lead titanate. New developments towards the consideration of hot excited carriers are under way.    

 
Phonon band structure: the polar instability at the Gamma point in dark (blue curve) becomes stable when electrons and holes are photo-excited (red curve).

Unité Mixte de Physique CNRS/Thales

Equipes de recherche

• UMPHY/Mat QT: Materials for the Quantum Technology of tomorrow

Activités de recherche

Quantum oxydes in 2D gases : towards Majorana fermions

Two-dimensional electron gases (2DEGs) based on SrTiO3 display remarkable properties such as Rashba spin-orbit coupling and superconductivity, both highly tunable by gate voltages. These 2DEGs constitute a unique platform for the production of Majorana fermions. The basic element of this technology is a quasi-unidimensional nanochannel, whose properties can be locally tuned by a gate to create topological and non-topological superconductors separated by metallic spacers or tunnel barriers. All the ingredients needed for the creation, the manipulation and the braiding of Majorana fermions can be produced using the same materials and integrated into architectures in a monolithic way.    

Possible STO-based device for the detection and manipulation of Majorana zero modes.

Hybrid superconductors for QT

Hybrid heterostructures combining superconductors and materials with remarkable electronic properties provide a natural ground for the emergence of new quantum states, which result from proximity effects and competing interactions. One of the systems of interest is the interface between superconductors and ferromagnets, where phenomena such as the emergence of a spin-polarized superconducting state or the coupling between magnetization dynamics and Josephson current can be observed. Another example is that of the interfaces between superconductors and topological insulators, for the generation of Majorana fermions. A specificity of our research in this field is the use of high temperature superconductors, whose d-wave symmetry enriches the physics and interface effects.    

Andreev pair interference pattern in the conductance on a d-wave/graphene Fabry-Pérot.
 

2D and Topology for QT

The use of 2D materials and molecules, intrinsically defined at the atomic scale, constitutes a natural emerging class of quantum materials. New electronic, magnetic and topological transport properties are emerging. Current research efforts focus on finding large-scale compatible quantum materials platforms for tomorrow's low-energy quantum technologies. They range from spin-dependent quantum interference at “spinterface” hybrid systems (such as molecular compounds or 2D interfaces) to gate control in newly discovered 2D quantum magnets and 2D topological insulators for the manipulation and quantum transport of spin (for instance in materials such as WTe₂/MoTe₂ or graphene QDots and atomic nanoribbons).    

 
Examples of 2D quantum materials integration in spintronic devices.

• UMPHY/Dispo QT : Novel opportunities for Quantum Devices based on spintronic & HTc supra

Magnonics for QT

Bose-Einstein condensate (BEC) of different types of quasi-particles has attracted a lot of interest in recent years. Their physics is based on the ability to significantly increase the density of quasi-particles by pumping. Magnon BEC is one of the few room- temperature manifestations of quantum coherence in solid-state physics. Such coherent state can only be reached in insulating magnetic materials (e.g. YIG) that possess extremely low magnon-phonon coupling. Furthermore, magnon superfluidity is also predicted to exist in particular classes of antiferromagnets. Magnons couple efficiently with their environment through EM radiation and can be interfaced with NV centres and superconducting qubits. Using the tunability offered by spintronic phenomena, we envision their potential integration in versatile hybrid quantum systems.     

An anticrossing of a magnons coherent mode with an electrodynamic mode measured using radiofrequency spectroscopy on the top of a diamond crystal.

Neuromorphique QT

Neuromorphic and quantum computing are both foreseen as the future of beyond-CMOS computation. Quantum neuromorphic computing aims at combining the advantages of these two approaches by implementing physical neurons on quantum devices. One research axis studies so-called spintronic Josephson junctions. Indeed, an original aspect of these new components is that at low temperature an antiferromagnetic Josephson junction behaves like an anharmonic quantum oscillator. By coupling several quantum junctions, it is possible to study the contribution of quantum complexity to computation with a reservoir, as has been done recently with classical spintronics oscillators. A parallel axis of research investigates the implementation of a quantum
reservoir on superconducting circuits.     

Quantum reservoir neural network exploits the dynamics of a disordered quantum system. Reservoir nodes are implemented by the quantum basis states of the system. A subset of these states are measured to provide the reservoir outputs.

Josephson devices for QT

The implementation of Josephson junctions in carefully- engineered arrays opens the door to a variety of electronic applications like quantum antennas, sensors or amplifiers, with properties unachievable using their classic counterparts. Furthermore, using high-critical-temperature superconductors allows compact, energy-efficient, and relatively cheap cryogenic packaging so that these devices can successfully transition to commercial quantum products. In addition, in a synergic effort with the “Hybrid superconductors” activity, tunable Josephson circuits are envisioned based on cuprates combined with ferromagnetic or 2D materials (graphene, topological insulators), in which properties can be manipulated by external stimuli (magnetic or electrical fields, light…).    

 
Truly-broadband and compact quantum antenna sensitive to the magnetic-field component of RF waves.