LKB SEMINARS/SÉMINAIRES DU LKB
Upcoming seminars – Séminaires à venir
29/05/2024  11am : Nathan Goldman (Laboratoire Kastler Brossel, Collège de France)
Title – Fractional quantum Hall physics in quantum simulators
Location : Amphi Budé – Collège de France – 11 Place Marcelin Berthelot – 75005
A coffee will be offered starting at 10:45 am (room 1), the seminar will start at 11am (amphi Budé)
Abstract – This talk will present recent progress in realizing and detecting fractional quantum Hall (FQH) states in quantum simulators, setting the focus on ultracold atoms in optical lattices. I will start by describing the state of the art, introducing key theoretical notions and reporting on recent experimental results. I will then present several methods for extracting topological signatures in these settings, both in the bulk and on the edge of the FQH droplet. I will also discuss different preparation schemes, introducing a patchwork construction for growing FQH states and an opensystem approach dubbed ‘coldatom elevator’. While directly relevant to cold atoms, the ideas and results presented in this talk could have implications for a broad class of quantum settings.
05/06/2024  11am : Gwendal Feve (Ecole Normale Supérieure)
Title – Fractional statistics of anyons in mesoscopic colliders
Location : Amphi Budé – Collège de France – 11 Place Marcelin Berthelot – 75005
A coffee will be offered starting at 10:45 am, the seminar will start at 11am
Abstract – In threedimensional space, elementary particles are divided between fermions and bosons according to the properties of symmetry of the wave function describing the state of the system when two particles are exchanged. When exchanging two fermions, the wave function acquires a phase. On the other hand, in the case of bosons, this phase is zero, . This difference leads to deeply distinct collective behaviors between fermions, which tend to exclude themselves, and bosons which tend to bunch together. The situation is different in twodimensional systems which can host exotic quasiparticles, called anyons, which obey intermediate quantum statistics characterized by a phase varying between and [1,2].
For example in the fractional quantum Hall regime, obtained by applying a strong magnetic field perpendicular to a twodimensional electron gas, elementary excitations carry a fractional charge [3,4] and have been predicted to obey fractional statistics [1,2] with an exchange phase (where is an odd integer). Using metallic gates deposited on top of the electron gas, beamsplitters of anyon beams can be implemented. I will present how the fractional statistics of anyons can be revealed in collider geometries, where anyon sources are placed at the input of a beamsplitter [5,6,7]. The partitioning of anyon beams is characterized by the formation of packets of anyons at the splitter output. This results in the observation of strong negative correlations of the electrical current, which value is governed by the anyon fractional exchange phase [5,8].
[1] B. I. Halperin, Phys. Rev. Lett. 52, 1583–1586 (1984).
[2] D. Arovas, J. R. Schrieffer, F. Wilczek, Phys. Rev. Lett. 53, 722–723 (1984).
[3] R. de Picciotto et al., Nature 389, 162–164 (1997).
[4] L. Saminadayar, D. C. Glattli, Y. Jin, B. Etienne, Phys. Rev. Lett. 79, 2526–2529 (1997)
[5] B. Rosenow, I. P. Levkivskyi, B. I. Halperin, Phys. Rev. Lett. 116, 156802 (2016).
[6] H. Bartolomei et al. Science 368, 173177 (2020).
[7] M. Ruelle et al., Phys. Rev. X 13, 011031 (2023).
[8] Lee, JY.M., Sim, HS, Nature Communications 13, 6660 (2022).
19/06/2024  11am :Roman Schnabel (Université Gottfried Wilhelm Leibniz de Hanovre)
Title – Optical and Optomechanical Quantum Correlations in operational Gravitational Wave Detectors
Location : Room 2 – Collège de France – 11 Place Marcelin Berthelot – 75005
A coffee will be offered starting at 10:45 am in room 4, the seminar will start at 11am in room 2.
Abstract – From 2010 to 2015, the gravitationalwave (GW) detector GEO600 was using squeezed light in all of its searches for GWs [1]. The successful sensitivity improvement triggered the implementation of “squeeze lasers” also in Advanced LIGO and Advanced Virgo. In 2019 they started their third observational run with an increased event rate of up to 50% due to the exploitation of squeezed states of light [2,3]. More recently, LIGO’s optical quantum noise was shown to be less than that at the Standard Quantum Limit (SQL) [4]. While a squeezed quantum uncertainty refers to quantum correlations in time, I will explain why the observation in [4] certifies correlations between the quantum uncertainties of the optical field and those of the motion of the 40 kg mirrors [5].
References
[1] LIGO Scientific Collaboration, Nature Physics 7, 962 (2011);
[2] M. Tse et al., Phys. Rev. Lett. 123, 231107 (2019);
[3] F. Acernese et al., Phys. Rev. Lett. 123, 231108 (2019);
[4] H. Yu et al., Nature 583, 43 (2020);
[5] R. Schnabel and M. Korobko, AVS Quantum Sci 4, 014701 (2022).
26/06/2024  11am : Kenji Ohmori (Institute for Molecular Science (IMS), National Institutes of Natural Sciences, Japan)
Title – Ultrafast quantum simulation and quantum computing with ultracold atom arrays at quantum speed limit
Location : Amphi Budé – Collège de France – 11 Place Marcelin Berthelot – 75005
A coffee will be offered starting at 10:45 am, the seminar will start at 11am
Abstract – Manybody correlations drive a variety of important quantum phenomena and quantum machines including superconductivity and magnetism in condensed matter as well as quantum computers. Understanding and controlling quantum manybody correlations is thus one of the central goals of modern science and technology. My research group has recently pioneered a novel pathway towards this goal with nearby ultracold atoms excited with an ultrashort laser pulse to a Rydberg state far beyond the Rydberg blockade regime [17]. We first applied our ultrafast coherent control with attosecond precision [2,3] to a random ensemble of those Rydberg atoms in an optical dipole trap, and successfully observed and controlled their strongly correlated electron dynamics on a subnanosecond timescale [1]. This new approach is now applied to arbitrary atom arrays assembled with optical lattices or optical tweezers that develop into a pathbreaking platform for quantum simulation and quantum computing on an ultrafast timescale [47].
In this ultrafast quantum computing, as schematically shown in Fig. 1, we have recently succeeded in executing a controlledZ gate, a conditional twoqubit gate essential for quantum computing, in only 6.5 nanoseconds at quantum speed limit, where the gate speed is solely determined by the interaction strength between two qubits [5]. This is faster than any other twoqubit gates with coldatom hardware by two orders of magnitude. It is also two orders of magnitude faster than the noise from the external environment and operating lasers, whose timescale is in general 1 microsecond or slower, and thus can be safely isolated from the noise. Moreover, this twoqubit gate is faster than the fast twoqubit gate demonstrated recently by “Google AI Quantum” with superconducting qubits [8].
References
[1] N. Takei et al., Nature Commun. 7, 13449 (2016).
Highlighted by Science 354, 1388 (2016); IOP PhyscisWorld.com (2016).
[2] H. Katsuki et al., Acc. Chem. Res. 51, 1174 (2018).
[3] C. Liu et al., Phys. Rev. Lett. 121, 173201 (2018).
[4] M. Mizoguchi et al., Phys. Rev. Lett. 124, 253201 (2020).
[5] Y. Chew et al., Nature Photonics 16, 724 (2022). (Front Cover Highlight)
[6] V. Bharti et al., Phys. Rev. Lett. 131, 123201 (2023).
[7] V. Bharti et al., arXiv:2311.15575 (2023).
[8] B. Foxen et al., Phys. Rev. Lett. 125, 120504 (2020).
03/07/2024  11am : Audrey Bienfait (École normale supérieure de Lyon)
Title – Implementing a quantum memory at microwave frequencies with Bismuth donors in silicon
Location : Amphi Budé – Collège de France – 11 Place Marcelin Berthelot – 75005
A coffee will be offered starting at 10:45 am in room 1, the seminar will start at 11am in the amphi Budé
Abstract – Among platforms for storing quantum states in the microwave domain, solid state spin ensembles addressed via superconducting circuits stand out for their multimodal storage capability and the secondlong coherence time when operated at clock transitions [1]. Successful implementation of a practical memory scheme requires several keys features, such as the ability to tune ondemand the frequency and the bandwidth of the resonator [2]. In this talk, we will present a superconducting circuit architecture accomplishing both, allowing strong coupling to an ensemble of bismuth dopants in silicon. We devise a parametric process to dynamically control the virtual bandwidth of the superconducting circuit by exploiting its kinetic inductance nonlinearity, demonstrating coupling rate tuning range over a factor of 15. The strong coupling of the spins to the resonator also set radiation loss as the main nspin relaxation channel. Combined with nuclear and electronic drives, this Purcell effect enables to polarize the spins dynamically predominantly into a single ground state, allowing us to reach a cooperativity between the resonator and the spin ensemble near unity.
References:
[1] Wolfowicz, G. et al. Nature nanotechnology 8, 561–564 (2013).
[2] Julsgaard, B. et al. Phys. Rev. Lett. 110, 250503 (2013).
Previous seminars – Séminaires passés
Date  Speaker  Title and abstract  Time and location 
2023/11/29 
Bruno LaburtheTolra(LPL, Paris Nord – CNRS) 
Quantum thermalization of large spin atoms in optical lattices Abstract – Our experimental projects at the Laser Physics Institute (North Paris University) aim at characterizing entanglement for manybody systems made of large spin atoms. For this, we have developed two experimental setups : one with largespin strontium fermionic atoms, with spinindependent contact interactions; one with largespin chromium bosonic atoms, with spindependent longrange dipoledipole interactions. Our experiments are mostly outofequilibrium experiments, where we probe how an isolated manybody quantum system relaxes towards equilibrium after being excited, in a scenario of quantum thermalization. I will first briefly describe our first measurements of the spin distribution of the SU(N) Fermi gas made of strontium atoms. For this, we used a spinorbit coupling scheme, where a retroreflected laser beam selectively diffracts two spin components in opposite directions. Spin sensitivity is provided by sweeping through a magneticfield sensitive transition while dark states ensure that spontaneous emission remains low. On the chromium machine, we investigated the spin dynamics and quantum thermalization of a macroscopic ensemble of S = 3 spins initially prepared in a pure coherent spin state. The experiment uses a unitfilled array of 10 thousand chromium atoms in a three dimensional optical lattice. Atoms interact at long distance under the effect of magnetic dipoledipole interactions, realizing the spin3 XXZ Heisenberg model with longrange couplings. We investigated the buildup of quantum correlations in this manybody system. For this, we measured collective properties such as the total population in the seven different Zeeman states, or the collective spin length. We also found that the measurement of magnetization fluctuations provides direct quantitative estimates for twobody correlations, and that bipartite measurements allow to characterize their anisotropy. 
11H SU – Jussieu 
Date  Speaker  Title and abstract  Time and location 
2023/11/15 
Hui Cao(Department of Applied Physics, Yale University) 
Mesoscopic physics of photons Abstract – Mesoscopic physics encompasses a broad spectrum of interference effects associated with the coherent wave propagation in complex systems. While this field initially emerged from investigations into electron transport, there are significant benefits to exploring the mesoscopic transport of photons. Through the manipulation of a coherent light’s wavefront, we are able to govern the propagation of light within randomly scattering media. For instance, this allows us to enhance light transmission or effectively deliver optical energy to targets by controlling the interference patterns of scattered waves. Another prominent manifestation of wave interference is Anderson localization, which signifies the halt of diffusive wave propagation in disordered systems. Despite four decades of extensive research, the question of whether threedimensional Anderson localization of electromagnetic waves exists has remained unanswered. Recent progress in hardwareaccelerated numerical computation allows us to conduct comprehensive, largescale simulations. Our findings affirm the nonexistence of threedimensional localization of vector electromagnetic waves in disordered dielectric systems, while highlighting the presence of Anderson localization in disordered metallic systems. Lastly, I will delve into the interplay between light localization and coherent amplification, which leads to the phenomenon of random lasing. 
11H SU – Jussieu 
2023/10/25 
Tracy NORTHUP(University of Innsbrück) 
Levitated nanoparticles: a route to the quantum regime Abstract – Can we prepare quantummechanical states of motion of macroscopic objects — for example, superposition states of massive objects where the distance scale of the superposition is as large as the object itself? Such states would allow us both to investigate fundamental questions about quantum mechanics and to build novel sensors and transducers. A levitated nanoparticle in ultrahigh vacuum is a promising experimental system with which to investigate these questions. I will present experimental work with silica nanoparticles in ion traps in which we aim to bring these particles into the quantum regime. Here, we adapt techniques originally developed for trapped atomic ions, including detection via selfinterference and sympathetic cooling, for the domain of nanoparticles [1,2]. Quality factors above 10^{10} provide evidence of the particles’ extreme isolation from their environment [3]. Recently, we have trapped a calcium ion and a nanoparticle together in a linear Paul trap [4], which provides a potential route to prepare the nanoparticle’s motion in nonclassical states.
[1] L. Dania, K. Heidegger, D. S. Bykov, G. Cerchiari, G. Arenada, T. E. Northup, Phys. Rev. Lett. 129, 013601 (2022) 
11H SU – Jussieu 
2023/10/18 
Lawrence CHEUK(Princeton University) 
Optical Tweezer Arrays of LaserCooled Molecules as a New Quantum Science Platform Abstract – Polar molecules, with their rich internal structure and tunable longrange interactions, have long been proposed for quantum information processing and quantum simulation of a wide range of manybody Hamiltonians. For these applications, the abilities to detect and manipulate individual particles are often useful and sometimes necessary. By offering microscopic detection and control at the singlemolecule level, optical tweezer arrays of polar molecules therefore promise to be a new versatile platform for quantum science. In this talk, I will report on several recent advances from our group on controlling individual lasercooled molecules trapped in rearrangeable tweezer arrays. I will describe our work on creating defectfree arrays of CaF molecules in 1D and observing coherent dipolar interactions between molecular pairs, and discuss how these results establish the building blocks for quantum information processing and simulation of quantum spin models. I will also describe our recent results towards full quantum control of lasercooled molecules including their motional degrees of freedom. Specifically, I will report our latest work demonstrating Raman sideband cooling in molecules for the first time, and discuss how it provides a new pathway towards lowentropy molecular ensembles through lasercooling. 
11H SU – Jussieu 
2023/10/04 
Andrea CAVALLERI(Max Planck Hamburg*) 
Recent Progress in Driven Superconductivity Abstract – I will discuss how irradiation of certain quantum materials with coherent electromagnetic radiation at TeraHertz and midinfrared frequencies can induce transient high temperature states that have striking similarities with equilibrium superconductors. These phases are observed at base temperatures as high as room temperature, underscoring the ability to impress coherence with light. This talk will also cover our search for new experimental methods that enable the characterization of these transient phases, to measure optical, structural, electrical and magnetic properties at very fast speeds. *Max Planck Institute for the Structure and Dynamics of Matter, Hamburg GERMANY 
11H SU – Jussieu 
Date  Speaker  Title and abstract  Time and location 
2023/07/12 
Martin ZWIERLEIN(Massachusetts Institute of Technology) 
Owls to Athens: Recent experiments on Rotating Bose Gases Abstract – Rapidly rotating quantum gases, pioneered at LKB, realize the physics of charged particles in high magnetic fields. We developed a novel protocol, geometric squeezing, that enables to create BoseEinstein condensates in a single Landau gauge wavefunction of the lowest Landau level. Based on the noncommutativity of guiding center X and Y coordinates, geometric squeezing in a saddle potential is a real space analogue to squeezing in phase space of an inverted 1D harmonic oscillator. The condensate’s transverse width shrinks to the Heisenberglimited groundstate extent of cyclotron motion. Removing the saddle enables studying the evolution of a Landau gauge condensate in « flat land » under the sole influence of interactions. Surprisingly, we find that Landau gauge condensates are unstable towards crystallization into arrays of droplets. This instability of states in the lowest Landau level has its classical analogy in the KelvinHelmholtz instability of counterflowing liquids. We explore the crossover of this instability from the lowest Landau level to the ThomasFermi regime. I will discuss experiments on observing edge states in confined geometries and prospects to extend this work beyond meanfield quantum Hall states of bosons. 
11H ENS – Lhomond 
2023/06/28 
Gerhard REMPE(MaxPlanck Institute of Quantum Optics, Germany) 
Massively entangled photonic graph states Abstract – Individually addressable atoms strongly coupled to optical cavities constitute lightmatter quantum modules with numerous applications in quantum information processing. The talk will present a new capability of the system as an efficient, highfidelity entanglement source for large photonic graph states. Unprecedented entanglement rates for more than a dozen photons are now stateoftheart. This opens up new perspectives for measurementbased quantum computation and losstolerant quantum communication. 
11H Collège de France 
2023/05/17 
Nicolas GISIN(Group of Applied Physics, University of Geneva, Switzerland) 
Quantum NonLocality in Networks Abstract – Quantum nonlocality, i.e. the violation of some Bell inequality, has proven to be an extremely useful concept in analyzing entanglement, quantum randomness and cryptography, among others. In particular, it led to the fascinating field of deviceindependent quantum information processing. Historically, the idea was that the particles emitted by various quantum sources carry additional variables, known as local hidden variables. The more modern view, strongly influenced by computer science, refers to these additional variables as shared randomness. This, however, leads to ambiguity when there is more than one source, as in quantum networks. Should the randomness produced by each source be considered as fully correlated, as in most common analyses, or should one analyze the situation assuming that each source produces independent randomness, closer to the historical spirit? The latter is known, for the case of n independent sources, as nlocality. For example, in entanglement swapping there are two sources, hence “quantumness” should be analyzed using 2locality (or, equivalently, bilocality). The situation when the network has loops is especially interesting. Recent results for triangular networks will be presented. Another result is that some quantum networks can’t be described by realnumber Hilbert spaces. 
11H Collège de France 
2023/05/17 
Francesca FERLAINO(University of Innsbruck and Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences) 
Manybody physics in dipolar quantum gases Abstract – Brought to quantum degeneracy, ultracold gases enable the study of manybody quantum phenomena, in which the interaction between atoms can be so carefully mastered as to determine the very state of matter. Typically, this interaction has a shortrange and isotropic nature, the latter meaning that the atoms globally attract or repel each other. However, there is another possibility that naturally emerges for some specific atomic species, such as erbium and dysprosium, featuring an extraordinarily large magnetic dipole moment. Magnetic properties give rise to dipolar manybody interactions, qualitatively very different from others in that it is longrange and anisotropic, thus adding connectivity and directionality at the quantum level. In the present talk I will retrace the fundamental steps in the study of dipolar gases, with emphasis on the Innsbruck results, from their creation to the new phenomena unveiled such as the emergence of rotonic excitations, so named by Landau, to the observation of a new and paradoxical state of matter with multiple spontaneous symmetry breaking, known as supersolid. 
11H Collège de France 
2023/03/01 
Martino TRASSINELLI(Institut des NanoSciences de Paris, CNRS, Paris, France) 
Testing quantum electrodynamics at extreme fields in the heaviest fewelectron atoms Abstract – Quantum electrodynamics (QED), the quantum field theory that describes the interaction between light and matter is commonly regarded as the best tested quantum theory in modern physics. However, this claim is mostly based upon extremely precise studies performed in the domain of relatively lowfield strengths and light atoms/ions. In the realm of very strong electromagnetic fields, as present e.g. in the heaviest highlycharged ions, QED calculations enter a qualitatively different nonperturbative regime (in Za with Z the nuclear charge and a the fine structure constant) with quantum vacuum fluctuations effects such as vacuum polarisation and selfenergy strongly affecting the atomic binding energies. Experimental studies on this regime are very challenging due to the required extremely high ionization state of the investigated ions. Therefore, at present, precision of QED tests in the nonperturbative strongfield domain still remains considerably lower as compared to the perturbative regime. For these endeavours, precise understanding of the structure of highlycharged ions is of great importance to test boundstate QED in strongest Coulomb fields. We present here the most recent experimental developments for measuring of transition energy in heavy, fewelectron atoms. In particular, we present a recent experiment on highaccuracy xray spectroscopy of two, three, and fourelectron uranium ions (Z=92, i.e. Za=0.7). The obtained experimental accuracy allows to test, on the one hand, twoloop quantum electrodynamics effects for the first time in heavy heliumlike atoms, and, on the other hand, to isolate the effects of electronelectron interaction in heavy bound systems. Such measurements rule out some of the most recent theoretical predictions. 
11H ENS – Lhomond 
2023/02/22 
Silke OSPELKAUS(Institut of Quantum Optics, Leibniz Universität Hannover, Germany) 
Quantum gases of ultracold polar molecules Abstract – In recent years, tremendous progress in the preparation and control of ultracold molecular gases in the quantum regime has been achieved and has opened exciting new research opportunities. Molecules rotate and oscillate and therefore offer many more quantum degrees of freedom than their atomic counterparts. Polar molecules interact via strong and longrange anisotropic interactions. These unique molecular properties lead to largely unexplored new possibilities and surprising results. These range from peculiar scattering properties via the control of ultracold collisions and chemical reactions to strongly correlated dipolar quantum manybody systems. In this talk I will take you on a journey through the world of cold and ultracold molecular systems and discuss future prospects. 
11H ENS – Lhomond 
2023/02/08 
Patrice BERTET(Université Paris Saclay, CEA Saclay, SPEC) 
Singleelectronspinresonance detection by microwave photon counting Abstract – Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities, with applications ranging from chemistry to quantum computing, but it gives access only to ensembleaveraged quantities due to its limited signaltonoise ratio. The sensitivity needed to detect single electron spins has been reached so far using spindependent photoluminescence, transport measurements, or scanningprobe techniques. These methods are systemspecific or sensitive only in a small detection volume, so that practical single spin detection remains an open challenge. Here, we demonstrate single electron spin resonance at millikelvin temperature by spin fluorescence detection [1], using a microwave photon counter at cryogenic temperatures based on a superconducting transmon qubit [2]. We detect individual paramagnetic erbium ions in a scheelite crystal coupled to a smallmodevolume, highquality factor superconducting resonator to enhance their radiative decay rate [3], with a signaltonoise ratio of 1.9 in one second integration time. The fluorescence signal shows antibunching, proving that it comes from individual emitters [4]. Coherence times up to 3ms are measured, limited by the ion radiative lifetime. The method applies to arbitrary paramagnetic species with long enough nonradiative relaxation time, and offers large detection volumes; as such, it may find applications in magnetic resonance and quantum computing [4].
[1] E. Albertinale et al., Nature 600, 434 (2021) [2] R. Lescanne et al., Phys. Rev. X 10, 021038 (2020) [3] A. Bienfait et al., Nature 531, 74 (2016) [4] Z. Wang et al., arXiv:2301.02653 (2023) 
11H Jussieu 
2023/01/18 
Philipp TREUTLEIN(Department of Physics, University of Basel, Switzerland) 
An EinsteinPodolskyRosen experiment with two BoseEinstein condensates Abstract – In 1935, Einstein, Podolsky and Rosen (EPR) conceived a Gedankenexperiment which became a cornerstone of quantum technology and still challenges our understanding of reality and locality today. While the experiment has been realized with small quantum systems, a demonstration of the EPR paradox with spatially separated, massive manyparticle systems had so far remained elusive. In our experiment, we observe the EPR paradox with two spatially separated BoseEinstein condensates containing about 700 Rubidium atoms each. Entanglement between the two condensates results in strong correlations between measurement outcomes of their collective spins, satisfying Reid’s criterion for the EPR paradox. Our results show that the conflict between quantum mechanics and local realism does not disappear as the system size is increased to over a thousand massive particles. Furthermore, EPR entanglement in conjunction with individual manipulation of the two condensates on the quantum level, as demonstrated here, constitutes an important resource for quantum metrology and information processing with manyparticle systems.
P. Colciaghi, Y. Li, P. Treutlein, and T. Zibold, EinsteinPodolskyRosen experiment with two BoseEinstein condensates, arXiv:2211.05101. 
11H Jussieu 
2022/12/07 
Jacqueline BLOCH(C2N Palaiseau*) 
Excitonic polaritons in semiconductor lattices: emulating condensed matter physics Abstract – Photonic resonators, coupled within a lattice, have appeared in the recent years as a powerful synthetic platform to imprint on light some of the fascinating physical properties that can emerge in condensed matter, or even to go beyond what exists in nature. For instance, light can become superfluid, present spin orbit coupling, spin Hall effect or propagate along topologically protected edge states. New physical properties may emerge when drive and dissipation come into play. Such realizations are not only interesting from a fundamental point of view, but also inspire innovative photonic devices. After a general introduction to excitonpolariton (polariton) physics and polariton lattices [1], I will present some recent experiments we have performed at C2N. Using lattices of semiconductor microcavities, we explore single and many body physics of photons in 1D or 2D lattices and the emergence of novel physics related to the openness of the system [2]. Topological physics can be investigated when nonlinearities come into play [3]. Interestingly, our photonic platform also enables exploring the physics of out of equilibrium Bose Einstein Condensates. We have recently shown that the coherence of these BECs features universal scaling related to the Kardar–Parisi–Zhang universality class [4].
[1] C. Ciuti and I. Carusotto, Quantum fluids of light, Rev. Mod. Phys. 85, 299 (2013) [2] A. Amo and J. Bloch, Excitonpolaritons in lattices: A nonlinear photonic simulator, Comptes Rendus de l’Académie des Sciences 8, 805 (2016) (Elsevier) [3] N. Pernet et al., Topological gap solitons in a 1D nonHermitian lattice, Nature Physics 18, 678 (2022) [4] Q. Fontaine et al., Observation of KPZ universal scaling in a onedimensional polariton condensate, Nature 608, 687 (2022)
* Center for Nanoscience and Nanotechnology (C2N), Université Paris Saclay / CNRS 
11H Jussieu 
2022/11/30 
Immanuel BLOCH(Max Planck Garching) 
Quantum Simulations using Ultracold Atoms in Optical Lattices Abstract – 40 years ago, Richard Feynman outlined his vision of a quantum simulator for carrying out complex calculations of physical problems. Today, his dream has become a reality and a highly active field of research across different platforms ranging from ultracold atoms and ions, to superconducting qubits and photons. In my lecture, I will outline how ultracold atoms in optical lattices started this vibrant and interdisciplinary research field 20 years ago and now allow probing quantum phases in and outofequilibrium with fundamentally new tools and single particle resolution. Novel (hidden) order parameters, entanglement properties, full counting statistics or topological features can now be measured routinely and provide deep new insight into the world of correlated quantum matter. I will introduce the measurement and control techniques and a few recent applications regarding quantum simulations of condensed matter systems, namely the Fermi Hubbard model, which plays an essential role in the context of HighTc superconductivity, experiments on new dynamical phases of matter, as well as topological systems. 
11H Jussieu 
2022/11/23 
Andreas WALLRAFF(Department of Physics, ETH Zurich, Switzerland) 
Realizing Quantum Error Correction with Superconducting Circuits* Abstract – Superconducting electronic circuits are ideally suited for studying quantum physics and its applications. Since complex circuits containing hundreds or thousands of elements can be designed, fabricated, and operated with relative ease, they are one of the prime contenders for realizing quantum computers. Currently, both academic and industrial labs vigorously pursue the realization of universal faulttolerant quantum computers. However, building systems which can address commercially relevant computational problems continues to require significant conceptual and technological progress. For faulttolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distancethree logical qubit building up on our recent distancetwo error detection experiments [1]. In an error correction cycle taking only 1.1 µs, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit and phaseflip error syndromes using a minimumweight perfectmatching algorithm in an errormodelfree approach and apply corrections in postprocessing. We find a low logical error probability of 3 % per cycle [2]. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast, and highperformance quantum error correction cycles, together with recent advances in ion traps, support our understanding that faulttolerant quantum computation will be practically realizable.
[1] C. Kraglund Andersen et al., Nature Physics 16, 875–880 (2020) [2] S. Krinner, N. Lacroix et al., Nature 605, 669–674 (2022)
* Work done in collaboration with Sebastian Krinner, Nathan Lacroix, Ants Remm, Agustin Di Paolo, Elie Genois, Catherine Leroux, Christoph Hellings, Stefania Lazar, Francois Swiadek, Johannes Herrmann, Graham J. Norris, Christian Kraglund Andersen, Markus Müller, Alexandre Blais, Christopher Eichler, and Andreas Wallraff 
11H Jussieu 
2022/11/16 
Päivi TÖRMÄ(Aalto University – Helsinki, Finland) 
New perspectives on quantum geometry, superconductivity and BoseEinstein condensation Abstract – Superconductivity, superfluidity and BoseEinstein condensation (BEC) are manybody phenomena where quantum statistics are crucial and the effect of interactions may be intriguing. Superconductors are already widely applied, but theoretical understanding of superconductivity and condensation in several real world systems is still a challenge, and superconductivity at room temperature remains a grand goal. We have discovered that superconductivity (superfluidity) has a connection to quantum geometry [1]. Namely, the superfluid weight in a multiband system has a previously unnoticed component which we call the geometric contribution. It is proportional to the quantum metric of the band. Quantum metric is connected to the Berry curvature, and this allows to relate superconductivity with the topological properties of the band. Using this theory, we have shown that superconductivity is possible also in a flat band where individual electrons would not move. Recently, we and other groups have shown [2,3] that these results are essential in explaining the intriguing observation of superconductivity in bilayer graphene and may eventually help realize superconductors at elevated temperatures. We have also explored the effect of quantum geometry on BoseEinstein condensation [4]. BoseEinstein condensation has been realized for various particles or quasiparticles, such as atoms, molecules, photons, magnons and semiconductor exciton polaritons. We have experimentally realized a new type of condensate: a BEC of hybrids of surface plasmons and light in a nanoparticle array [5]. The condensate forms at room temperature and shows ultrafast dynamics, and the system provides easy tunability of the lattice and unit cell geometry and symmetries. Recently, we have observed formation of polarization textures and domain walls, and obtained the BEC phase for the first time using a phase retrieval algorithm [6]. Our measurements of spatial and temporal coherence show a change from exponential decay to powerlaw when crossing to the BEC phase [7]. We have also observed topological bound states of continuum (BICs) and lossdriven topological transitions in nanoparticle arrays [8].
[1] S. Peotta, P. Törmä, Nature Commun. 6, 8944 (2015); A. Julku, S. Peotta, T.I. Vanhala, D.H. Kim, P. Törmä, Phys. Rev. Lett. 117, 045303 (2016); P. Törmä, L. Liang, S. Peotta, Phys. Rev. B 98, 220511(R) (2018): K.E. Huhtinen, J. HerzogArbeitman, A. Chew, B.A. Bernevig, P. Törmä, Phys. Rev. B Editor’s Suggestion arXiv:2203.11133 (2022) [2] A. Julku, T.J. Peltonen, L. Liang, T.T. Heikkilä, P. Törmä, Phys. Rev. B 101, 060505(R) (2020); X. Hu, T. Hyart, D.I. Pikulin, E. Rossi, Phys. Rev. Lett. 123, 237002 (2019); F. Xie, Z. Song, B. Lian, B.A. Bernevig, Phys. Rev. Lett. 124, 167002 (2020); for a news article see L. Classen, Physics 13, 23 (2020) https://physics.aps.org/articles/v13/23 [3] P. Törmä, S. Peotta, B.A. Bernevig, Nat. Rev. Phys., https://doi.org/10.1038/s4225402200466y (2022) [4] A. Julku, G.M. Bruun, P. Törmä, Phys. Rev. Lett., 127, 170404 (2021) [5] T.K. Hakala, A.J. Moilanen, A.I. Väkeväinen, R. Guo, J.P. Martikainen, K.S. Daskalakis, H.T. Rekola, A. Julku, P. Törmä, Nature Phys. 14, 739 (2018); A.I. Väkeväinen, A.J. Moilanen, M. Necada, T.K. Hakala, P. Törmä, Nature Commun. 11, 3139 (2020) [6] J.M. Taskinen, P. Kliuiev, A.J. Moilanen, P. Törmä, Nano Letters 21, 5202 (2021) [7] A.J. Moilanen, K.S. Daskalakis, J.M. Taskinen, P. Törmä, Phys. Rev. Lett. 127, 255301 (2021) [8] R. Heilmann, G. Salerno, J. Cuerda, T.K. Hakala, P. Törmä, ACS Photonics 9, 224 (2022); G. Salerno, R. Heilmann, K. Arjas, K. Aronen, J.P. Martikainen, P. Törmä, arXiv:2206.08897 (2022) 
11H Jussieu 
2022/11/09 
Gerardo ADESSO(University of Nottingham) 
Every quantum helps Abstract – What makes quantum technologies tick? Advantages in communication, computation, metrology and other applications can be traced back to distinct manifestations of quantum theory, such as coherence and entanglement. We characterise these elusive quantum signatures and their operational power under the unifying lens of resource theories. We then show that every (convex) quantum resource yields an advantage in a channel discrimination task, enabling a strictly greater success probability than what is achievable by any state without the given resource. We further discuss recent progress in untapping these benefits for practical quantumenhanced imaging and sensing tasks 
11H Jussieu 
2022/10/26 
Rainer BLATT(University of Innsbruck)* 
The Quantum Way of Doing Computations, Simulations and Measurements Abstract – In this talk, the basic functional principles of quantum information processing are reviewed and the stateoftheart of the Innsbruck trappedion quantum computer is reported. With strings of trapped ions, we implement a quantum information processor and perform quantum operations. We present an overview on the available quantum toolbox and discuss the scalability of the approach. The quantum way of doing computations is illustrated with analog and digital quantum simulations. Employing universal quantum computations, we investigate the dynamics of the Lattice Schwinger model [1], a gauge theory of 1D quantum electrodynamics and using a hybridclassical ansatz, we determine steadystate properties of the Hamiltonian [2]. Using tailored quantum operations, we obtain optimized measurements for spectroscopy [3].
[1] E. A. Martinez et al., Nature 534, 516 (2016). [2] C. Kokail et al., Nature 569, 355–360 (2019). [3] C. Marciniak et al., Nature 603, 604 (2022).
*Inst. for Experimental Physics, University of Innsbruck and IQOQI Innsbruck, Austrian Academy of Sciences 
11H Jussieu 
2022/10/19 
Barbara TERHAL(TU Delft)* 
Quantum Error Correction: Dream or Nightmare Abstract – I will discuss the ideas behind quantum error correction. I will give an overview of some recent research on quantum error correction with superconducting qubits. In particular I will discuss the problem of qubit leakage as well as the alternative of bosonic error correction.
*QuTech & EEMCS Dept. Delft University of Technology 
11H Jussieu 
Date  Speaker  Title and abstract  Time and location 
06/15/22 
Klaus Blaum(MaxPlanck Heidelberg) 
Precision Tests of Fundamental Interactions and Their Symmetries using Exotic Ions in Penning Traps An overview is given on recent mass and gfactor measurements with extreme precision on single or few cooled ions stored in Penning traps. On the one hand, mass measurements provide crucial information for atomic, nuclear and neutrino physics as well as for testing fundamental interactions and their symmetries. On the other hand, gfactor measurements of the bound electron in highly charged hydrogenlike ions allow for the determination of fundamental constants and for constraining Quantum Electrodynamics. For example, the most stringent test of CPT symmetry in the baryonic sector could be performed by mass comparison of the antiproton with H and the knowledge of the electron atomic mass could be improved by a factor of 13. 
13H45 CDF 
06/22/22 
Robin Kaiser (University of Cambridge) 
Resonant dipoledipole interactions: Dicke subradiance and Anderson localisation
The quest for Anderson localization of light in three dimensions has been at the center of many experimental and theoretical activities. Cold atoms have emerged as interesting quantum system to study coherent transport properties of light. Initial experiments have established that dilute samples with large optical thickness allow studying weak localization of light, which has been well described by a mesoscopic model. Recent experiments on light scattering with cold atoms have shown that Dicke super or subradiance occurs in the same samples, a feature not captured by the traditional mesoscopic models. The use of a long range microscopic coupled dipole model allows to capture both the mesoscopic features of light scattering and Dicke super and subradiance in the single photon limit. I will review experimental and theoretical state of the art on the possibility of Anderson localization of light by cold atoms.

13H45 CDF 
06/06/22 
Zoran Hadzibabic (University of Cambridge) 
Far from equilibrium homogeneous Bose gases
The developments in trapping ultracold atomic gases in the homogenous potentials of optical box traps have opened many new research possibilities. One large research area where boxtrapping has been particularly advantageous is the study of nonequilibrium manybody physics, with different experiments investigating quenched, continuously driven and/or intrinsically unstable systems. I will discuss our recent experiments on turbulence in driven 3D and 2D Bose gases, and on the equilibration dynamics in a quenched 3D Bose gas, pointing out some similarities between the two.

13H45 CDF 
05/25/22 
Klaus Mølmer (University of Aarhus, Denmark) 
Quantum interactions with light that moves Protocols for scalable quantum information processing employ photon or phonon wave packets that can communicate quantum states and gate operations between distant material quantum systems in a larger network. The precise description of how travelling pulses of quantum radiation interact with a local material quantum system would seem a crucial and well established theory component in quantum optics and quantum information technologies. I shall discuss why and how a fundamental theory for such processes must differ from the treatment of interactions between, e.g., an atom and standing wave modes in cavity QED. In fact, no textbook provides a formal description of this elementary interaction process. We have recently been able to cast the problem in a form that permits a (simple) density matrix theory for the excitation of a general quantum system by an incident quantum pulse of radiation. Our theory also provides the output quantum state of the radiation, restricted to any choice of a single or a few wave packet modes. I shall show multiple applications of this theory of relevance to recent experiments with atomic and superconducting qubits interacting with pulses of optical, microwave and acoustic radiation.  13H45 ENS 
18/05/22 
David Clément (Laboratoire Charles Fabry – Institut d’Optique) 
The fate of the Bogoliubov’s pairs at increasing interactions
A cornerstone in the description of quantum fluids is Bogoliubov’s theory, which provides a physical framework explaining how superfluidity emerges from interactions in ensembles of weaklyinteracting bosons. At the microscopic level, it predicts that interactions deplete the condensate by promoting pairs of bosons with opposite momenta outside the condensate, the quantum depletion. Exploiting the capability to detect individual metastable Helium atoms after a long free expansion, we confirmed this microscopic prediction experimentally. I shall present the measurements performed to reveal Bogoliubov’s pairs, a manifestation of interactioninduced quantum fluctuations at equilibrium, and their properties.
While Bogoliubov’s theory was introduced in the context of superfluid liquid Helium, interactions in liquid Helium deplete too strongly the condensate for Bogoliubov’s theory to be applicable. This naturally raises the question of the fate of the Bogoliubov’s pairs in a regime of strong depletion of the condensate. Varying the optical landscape where metastable Helium atoms are held, we have studied how the pairing signal changes as interactions increase and the gas become more correlated. I shall discuss this recent results, as well as ongoing efforts to observe atom triplets and quadruplets, in addition to atom pairs.

13H45 ENS 
Date  Speaker  Title and abstract  Time and location 
17/06/20 
Piet O. Schmidt(Universität Hannover)

Optical Clocks with Highly Charged Ions for Tests of Fundamental Physics
Highly charged ions (HCI) have many favorable properties for tests of fundamental physics and as potential nextgeneration optical atomic frequency standards [1]. For example, narrow optical finestructure transitions have smaller polarizabilities and electric quadrupole moments, but much stronger relativistic, QED and nuclear size contributions to their binding energy compared to their (near) neutral counterparts. Therefore, HCI have been found to be among the most sensitive atomic species to probe for a possible variation of the finestructure constant or dark matter coupling.

Visioconférence 
Date  Speaker  Title and abstract  Time and location 
10/06/20 
Tilman Pfau(University of Stuttgart)

Quantum Droplets and Supersolidity in a Dipolar Quantum Gas
Dipolar interactions are fundamentally different from the usual van der Waals forces in real gases. Besides the anisotropy the dipolar interaction is nonlocal and as such allows for self organized structure formation. In 2005 the first dipolar effects in a quantum gas were observed in an ultracold Chromium gas. By the use of a Feshbach resonance a purely dipolar quantum gas was observed three years after [1]. Recently it became possible to study degenerate gases of lanthanide atoms among which one finds the most magnetic atoms. Similar to the Rosensweig instability in classical magnetic ferrofluids selforganized structure formation was expected. In our experiments with quantum gases of Dysprosium atoms we could observe the formation of a droplet crystal [2]. In contrast to theoretical mean field based predictions the superfluid droplets did not collapse. We find that this unexpected stability is due to beyond meanfield quantum corrections of the LeeHuangYang type [3,4]. We observe and study selfbound droplets [5] which can interfere with each other. We also observe selforganized stripes in a confined geometry [6] and collective scissors mode oscillations of dipolar droplets [7Recently in the striped phase also phase coherence was observed in Dysprosium and Erbium experiments, which is evidence for a supersolid state of matter [8]. Upon crossing the transition to the dipolar supersolid a Goldstone mode appears, which we have observed recently [9]. The existence of this mode proofs the superfluid stiffness or the socalled phase rigidity of this new state of matter. Despite the lack of symmetry protection, also a Higgs mode was predicted to be observable in a finite system [10]. References [1] T. Lahaye, et al., Rep. Prog. Phys. 72, 126401 (2009) [2] H. Kadau, et al., Nature 530, 194 (2016) [3] T.D. Lee, K. Huang, and C. N. Yang, Phys. Rev. 106, 1135 (1957), D.S. Petrov, Phys. Rev. Lett. 115, 155302 (2015). [4] I. FerrierBarbut, et al., Phys. Rev. Lett. 116, 215301 (2016) [5] M. Schmitt, et al., Nature 539, 259 (2016) [6] M. Wenzel, et al., Phys. Rev. A 96 053630 (2017) [7] I. FerrierBarbut, et al., Phys. Rev. Lett. 120, 160402 (2018) [8] F. Böttcher, et al. Phys. Rev. X. 9, 011051 (2019), see also L. Tanzi, et al. Phys. Rev. Lett. 122, 130405 (2019), L. Chomaz et al., Phys. Rev. X 9, 021012 (2019) [9] M. Guo, et al. Nature. 574, 386–389 (2019) [10] J. Hertkorn et al., Phys. Rev. Lett. 123, 193002 (2019 
Visioconférence 
Date  Speaker  Title and abstract  Time and location 
04/03/20 
Valery Nesvizhevsky(Institut LaueLangevin)

Gravitational quantum states of light neutral particles
Gravitational Quantum States (GQS) and WhisperingGallery Quantum (WGS) states of light neutral particles are a useful tool for highprecision measurements. Such quantum states of neutrons have been observed [1] and used ourdays by several research groups to constrain fundamental shortrange interactions. Analogous states of ultracold atoms and antiatoms have been predicted [2]; they appear due to quantum reflection of ultracold (anti)atoms from surface [3]. Studies with hydrogen is the goal of a new GRASIAN collaboration. Those with antihydrogen can be pursuit in the future by GBAR collaboration at CERN in more precise experiments, which test the equivalence principle with antimatter [4]. In all these cases, a long observation time thus a much better energy resolution and precision can be achieved in a novel MagnetoGravitational Trap (MGT), where the particles will be trapped vertically by gravity and a mirror, and horizontally by a magnetic field [5]. The ultralow energies of (anti)atoms and long lifetimes of GQS provide unique conditions for precision gravitational, optical and hyperfine spectroscopy of (anti)atoms. In this talk we will discuss some experimental and theoretical results as well as prospects of these activities 1. V.V. Nesvizhevsky et al, Quantum states of neutrons in the Earth’s gravitational field, Nature 415 (2002) 297; Neutron whispering gallery, Nature Phys. 6 (2010) 114. 2. A.Yu. Voronin et al, Gravitational quantum states of antihydrogen, Phys. Rev. A 83 (2011) 032903. 3. P.P. Crepin et al, Quantum reflection of antihydrogen from a liquid helium bulk, Hyperf. Int. 240 (2019) 58. 4. P.P. Crepin et al, Quantum interference test of the equivalence principle of antihydrogen, Phys. Rev. A 99 (2019) 042119. 5. V.V. Nesvizhevsky et al, A magnetogravitational trap for precision studies of gravitational quantum states ), arXiv:200106332 (2020). 
Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris 
Date  Speaker  Title and abstract  Time and location 
26/02/20 
Juliette Simonet(University of Hamburg)

Ultracold meets Ultrafast
Ultrashort laser pulses grant access to an instantaneous and controlled creation of electrons and ions in a quantum gas. A single femtosecond laser pulse can ionize up to several thousand atoms, thus triggering the formation of strongly coupled ultracold plasmas. We report on the observation of ultrafast electron cooling in an expanding microplasma from 5000 K to about 1 K within less than one picosecond. Our experimental setup allows measuring the electronic kinetic energy distribution with meV resolution. Furthermore, we have performed numerical simulations of the plasma dynamics that are in excellent agreement with the measurements and provide insights into the thermalization mechanisms on subnanosecond timescales. 
Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris 
19/02/20 
Markus Aspelmeyer(University of Vienna)

Quantum Optical Control of Levitated Solids: a novel probe for the gravityquantum interface
The increasing level of control over motional quantum states of massive, solidstate mechanical devices opens the door to an hitherto unexplored parameter regime of macroscopic quantum physics. I will report on our recent progress towards controlling levitated solids in the quantum regime. I will discuss the prospects of using these systems for fundamental tests of physics, including the interface between quantum and gravitational physics. 
Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris 
12/02/20 
Michael Köhl(University of Bonn)

Quantum simulation of the twodimensional Hubbard model
Understanding strongly correlated quantum manybody systems remains a challenge both for experiment and theory. In particular, the interplay of interactions, kinetic energy, and dimensionality is complex and governs the occurrence and properties of lowtemperature quantum phases. A paradigmatic example of a strongly correlated manybody problem is that of interacting spin1/2 fermions on a periodic lattice. Depending on the Hamiltonian parameters, different quantum phases are realized. For example, for weak interactions and low filling of the lattice, the fermions delocalize into Bloch waves and constitute a metallic state with finite charge compressibility. In contrast, for strong repulsive interactions at half filling the fermions form a Mott insulator that occurs when the kinetic energy can no longer overcome the energy gap due to repulsive onsite interactions. In this talk, I will review the latest results from our lab of exploring this physics. 
Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris 
Date  Speaker  Title and abstract  Time and location 
20/11/2019 
Olivier Arcizet(Institut Néel)

Nanooptomechanics with vibrating nanowires
We will present our recent developments in the realisation of ultrasensitive vectorial force field sensors based on suspended silicon carbide nanowires, at room and dilution temperatures. We will introduce a universal measurement method where the 2D force field gradients are determined from the modifications of the nanowire eigenfrequencies and eigenvector orientations they induce [1]. In particular we will analyse the impact of nonconservative (rotational) force fields on the nanowire dynamics: leading to eigenmode orthogonality breaking, noise reduction and violation of the fluctuation dissipation relation [2]. We will then present how those exceptional force sensors can be implemented in a cavity nanooptomechanical experiment where we giant coupling strength achieved opens the road towards optomechanical experiments in the single photon regime. [1] L. Mercier de Lépinay et al, Nature Nanotech. 12, 156 (2017) [2] L. Mercier de Lépinay et al, Nature Comm. 9, 1401(2018) [3] F. Fogliano et al, arxiv 1904.01140 (2019) 
Sorbonne université – Campus jussieu – 4, place jussieu – 75005 Paris – 20th november at 13h45, room : T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
06/11/2019 
Arno Rauschenbeutel(HumboldtUniversität – Berlin)

Generation of correlated photons using noninteracting atoms weakly coupled to a guided optical mode
Typical schemes for generating correlated states of light require a highly nonlinear medium that is strongly coupled to an optical mode. However, unavoidable dissipative processes, which cause photon loss and blur nonlinear quantum effects, often impede such methods. In this seminar, I will report on a recent experimental demonstration of the opposite approach [1]. Using a strongly dissipative, weakly coupled medium, we generate and study strongly correlated states of light. Specifically, we study the transmission of resonant light through an ensemble of noninteracting atoms that weakly couple to a guided optical mode. Dissipation removes uncorrelated photons while preferentially transmitting highly correlated photons created through collectively enhanced nonlinear interactions. As a result, the transmitted light constitutes a strongly correlated manybody state of light, revealed in the secondorder correlation function. The latter exhibits strong antibunching or bunching, depending on the optical depth of the atomic ensemble. The demonstrated mechanism opens a new avenue for generating nonclassical states of light and for exploring correlations of photons in nonequilibrium systems using a mix of nonlinear and dissipative processes. Furthermore, our scheme may turn out transformational in quantum information science. For example, it offers a fundamentally new approach to realizing single photon sources, which may outperform sources based on single quantum emitters with comparable coupling strength. 
Sorbonne université – Campus jussieu – 4, place jussieu – 75005 Paris – 13th november at 13h45, room : T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
06/11/2019 
Carsten Klempt(Institut für Quantenoptik, Leibniz Universität Hannove)

Entanglement in spinor BoseEinstein condensates
Spinchanging collisions can be employed for the generation of entanglement in spinor BoseEinstein condensates, in close analogy to optical parametric downconversion. I will present the creation of two types of entangled states, TwinFock states and twomode squeezed states. Both states can be applied for interferometry beyond the Standard Quantum Limit. We have demonstrated that such entangled states can be separated in the spatial domain to transfer the entanglement from internal to external degrees of freedom [1]. I will discuss methods to employ spinentangled BoseEinstein condensates for inertially sensitive atom interferometers. [1] K. Lange, J. Peise, B. Lucke, I. Kruse, G. Vitagliano, I. Apellaniz, M. Kleinmann, G. Toth, C. Klempt, Entanglement between two spatially separated atomic modes, Science 360, 416 (2018). 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 6th of november at 13:45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
30/10/2019  Leonardo Fallani
(LENS, Florence)

Synthetic quantum systems with multicomponent atoms
Ultracold gases of neutral atoms provide a powerful technological platform for engineering synthetic manybody quantum systems. In a “quantum simulation” perspective, it is possible to control the atomic state to provide direct experimental realizations of prototypical theoretical models and to achieve “extreme” states of matter with no counterpart in conventional materials. I will give an introduction to the new approaches that are opened by the coherent, optical manipulation of internal states in ultracold Fermi gases of twoelectron atoms. I will review quantum simulation approaches for the realization of gauge fields and topological systems based on the concept of “synthetic dimensions” and I will discuss ongoing experiments with multicomponent Hubbard systems with SU(N) and SU(N)broken interaction symmetries. 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 30th of octobre at 13:45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
23/10/2019  Mete ATATURE (University of Cambridge) 
SolidState Quantum SpinPhoton Interfaces: Old Friends & New Abstract : Optically active spins in solids offer exciting opportunities as scalable and feasible quantumoptical devices. Numerous material platforms including diamond, semiconductors, and atomically thin 2d materials are under investigation, where each platform brings some advantages of control and feasibility along with other challenges. The inherently mesoscopic nature of solidstate platforms leads to a multitude of dynamics between spins, charges, vibrations and light. Implementing a high level of control on these constituents and their interactions with each other creates exciting opportunities for realizing stationary and flying qubits within the context of spinbased quantum information science, as well as investigating mesoscopic quantum systems. Quantum optics, developed originally for atomic systems, provides a very valuable toolbox for this endeavour. In this talk, I will provide a snapshot of the progress and challenges for two contrasting examples for spinphoton interfaces, namely semiconductor quantum dots and confined excitons in atomically thin materials. For the former, I will focus on a method to suppress the magnetic noise of the nuclear ensemble by an effective cooling mechanism. This method yields access to the nuclear sideband resolved regime and coherent coupling between a single electron spin and the nuclear ensemble. For the latter, I will discuss ways to deterministically trap longlasting confined excitons acting as artificial atoms, as well as their integration into optoelectronic devices. 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 23rd of octobre at 13h45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
16/10/2019  Charles ADAMS
(DurhamNewcastle)

Rydberg atoms for everything Abstract : This talk will begin with a brief review of the attractive features of Rydberg atoms for applications in quantum technology [CS Adams et al., arXiv:1907:09231]. Subsequently, the details of three experimental platforms being pursued in Durham will be discussed: First arrays of lightmatter interfaces with quasideterministic control of photonphoton interactions [H Busche et al., Nature Phys. 13, 655 2017], second terahertz imaging using terahertzto optical conversion [L. A. Downes et al. arXiv:1903.01308], and third arrays of individual Sr atoms [NC Jackson et al., arXiv:1904:03233]. 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 16th of octobre at 13h45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
09/10/2019  Claudio CONTI
(University Sapienza – Rome, IT)

Wave complexity and computation Abstract : We discuss the links between wave propagation and spin glasses, with particular emphasis on the realization of Ising machines, i.e., optical devices to solve combinatorial optimization. Recent developments challenge the performances of quantum annealers in solving NPcomplete problems, and we discuss a simple experimental approach that may potentially scale to millions of logical spins. We also review some unconventional applications of reservoir computing to study cancer morphodynamics by using simple optical neural networks with random media. Specifically, we compare the characterization of tumor spheroids obtained by conventional biophysical methods and the signals obtained by a recurrently trained disordered photonic device. We outline the relation with modern machine learning paradigms. 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 9th of octobre at 13h45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
02/10/2019  Alexia AUFFEVES
(Institut Néel)

Quantum Thermodynamics: From Measurement Driven Engines to Energetics of Quantum Control Abstract : Quantum Thermodynamics is an emerging and interdisciplinary field, that is currently building its own concepts with material taken from quantum information, quantum open systems, stochastic and information thermodynamics. It addresses a vast range of questions, whether fundamental or applied, e.g. What is the nature of time arrow at the quantum scale? How does it impact the efficiency of quantum engines? Are quantum coherence and entanglement new energetic resources? What is the energetic bill to run a quantum protocol?…In this colloquium I will provide an overview of the genesis, concepts and main motivations of this emerging field. I will focus on a recent proposal of Maxwell’s demon engine where work is not extracted from thermal fluctuations, but quantum fluctuations induced by quantum measurement only [1].This “measurement driven engine” has unlocked a new research line and offers a striking illustration of the thermodynamic footprint of measurement in the quantum regime, which acts as the ultimate source of randomness, irreversibility, and energy [2]. I will then switch to the autonomous version of this engine, where work is extracted from an engineered bath acting as a source of energy and coherence [3]. This last proposal sheds new light on how coherence impacts work extraction in the quantum regime. I will finally focus on the opposite side of quantum thermodynamics as a tool to assess the energetic cost of running quantum protocols against quantum noise [4]. References [1] Elouard, HerreraMarti, Huard, Auffèves, “Extracting work from quantum measurement in Maxwell’s demon engines”, PRL 118, 260603 (2017) 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 2th of octobre at 13h45, room T44/54 107 1er floor 
Date  Speaker  Title and abstract  Time and location 
18/09/2019  Monika Schleier Smith

Choreographing Quantum Spin Dynamics with Light Abstract : The dream of the quantum engineer is to have an “arbitrary waveform generator” for designing quantum states and Hamiltonians. Motivated by this vision, I will report on advances in optical control of longrange interactions among cold atoms. By coupling atoms to light in an optical resonator, we induce tunable nonlocal spinspin interactions, characterizing the resulting dynamics by realspace imaging. Notably, in a spin1 system, we observe photonmediated spin mixing, a new mechanism for producing correlated atom pairs. In a separate platform, we employ Rydberg dressing to induce Ising interactions in a dilute gas of cesium atoms in their hyperfine clock states, enabling the realization of a Floquet transversefield Ising model. I will discuss prospects in quantum simulation and quantum metrology promised by the versatility of optical control.[1] Ar39 dating with small samples provides new key constraints on ocean ventilation, Nature Comm. 9, 5046 (2018).[2] Observation of universal dynamics in a spinor Bose gas far from equilibrium, Nature 563, 217 (2018). 
Sorbonne université – Campus Jussieu – 4, place Jussieu – 75005 Paris – 18th of september at 13h45, amphi Charpak 
Date  Speaker  Title and abstract  Time and location 
02/07/2019  Andrey Surzhykov

Hyperfine structure of doubly ionized Th ion Abstract : The thorium nucleus with a mass number A = 229 attracts currently much interest because of its extremely lowlying first excited state. The existence of this nuclear isomeric state with excitation energy of about 8 eV opens the possibility for the development of a nuclear clock. Both the exact energy of the isomeric state as well as its nuclear magnetic dipole and electric quadrupole momenta are subjects of intense research. The latter can be determined by investigating the hyperfine structure of thorium atoms or ions. In this contribution we will discuss recent combined experimental and theoretical investigation of the hyperfine structure of the doubly ionized Th ion. We will see how the detailed analysis of the hyperfine structure allows one to extract accurate values of the nuclear momenta of the thorium isomeric state. 
Collège de France – 11, place Marcelin Berthelot – 75005 Paris, Room 2 : July 2nd, at 13:45 
Date  Speaker  Title and abstract  Time and location 
24/06/2019 
Pacôme Delva 
Fundamental physics and geodesy with atomic clocks At the beginning of the 20th century the theories of special and general relativity were developed by Einstein and his contemporaries. These physical theories revolutionize our conceptions of time and of the measurement of time. The atomic clocks, which appeared in the 1950s, are so accurate and stable that it is now essential to take into account many relativistic effects. The development and worldwide comparisons of such atomic clocks allowed for some of the most stringent of fundamental physics, as well as new ideas for the search of dark matter, which I will present in this talk. On a more applied level, when taking general relativity for granted, distant comparisons of atomic clocks can be used for navigation and positioning, as well as the determination of the geopotential. I will show how the chronometric observables can fit and be used within the context of classical geodesy. 
Collège de France – 11, place Marcelin Berthelot – 75005 Paris, Room 2 : June 24, at 13:45 
Date  Speaker  Title and abstract  Time and location 
05/06/2019  Iacopo Carusotto (INOCNR BEC Center, Trento) 
Strongly correlated quantum fluids of light
In this talk I will review the recent advances in the theoretical and experimental study of quantum fluids of light. This novel form of quantum matter consists of assemblies of photons that display collective manybody effects as a result of the optical nonlinearity of the underlying material. 
13:45, Collège de France 11, place MarcelinBerthelot – 75005 Paris, Room : Amphithéâtre Guillaume Budé 
Date  Speaker  Title and abstract  Time and location 
04/04/2019  Markus Oberthalter University of Heidelberg 
Quantum Atom Optics: Ocean & Universality in Quantum DynamicsThe experimental platform of atoms manipulated by light offers answers to a broad spectrum of open questions. With two explicit and very different examples I will give you a glimpse how broad this spectrum is. I will start with a fundamental question in oceanography: At what time has the deep water in the ocean been in exchange with the atmosphere? Quantum atom optics offers the experimental possibility to detect the very rare Argon 39 atoms one by one and with that allows the dating of water samples as small as ten liters [1]. A very different question in physics is about the existence of universal behavior. Specifically in respect to time dynamics this has only recently been discussed theoretically in the context of the early phase of after a heavy ion collision. Universal meaning, that the evolution does not depend on the initial condition and follows the scaling hypothesis in time and space. I will introduce the concept and present the first observation of this phenomenon in highly controlled ultracold Bose gases [2].
[1] Ar39 dating with small samples provides new key constraints on ocean ventilation, Nature Comm. 9, 5046 (2018).[2] Observation of universal dynamics in a spinor Bose gas far from equilibrium, Nature 563, 217 (2018) 
13:45, Collège de France 11, place MarcelinBerthelot – 75005 Paris, Room : 2 
Date  Speaker  Title and abstract  Time and location 
27/03/2019  Laurent Daudet (Light On) 
Optical random features for largescale machine learning
The propagation of coherent light through a thick layer of scattering material is an extremely complex physical process. However, it remains linear, and under certain conditions, if the incoming beam is spatially modulated to encode some data, the output as measured on a sensor can be modeled as a random projection of the input, i.e. its multiplication by an iid random matrix. One can leverage this principle for compressive imaging, and more generally for any data processing pipeline involving largescale random projections. This talk will discuss recent technological developments of optical coprocessors within the startup LightOn, and present a series of proof of concept experiments in machine learning, such as transfer learning, change point detection, or recommender systems. 
13:45, ENS – 24, rue Lhomond – 75005 Paris, Room : IV 
Date  Speaker  Title and abstract  Time and location 
20/03/2019  Dieter Meschede University of Bonn 
Few Atom Systems on the Route towards Quantum Technology?
In the so called bottomup approach to controlled atomic quantum matter small quantum systems are synthesized involving single, few or many atom systems. I will discuss two examples: I will show that controlled interaction of atoms with a so called fast optical resonators leads not only to a strongly preferred emission of light into optical wave guides (Purcell effect) but also to speed higher than conventional atomic decay rates. This device will be useful for future interconnects in hybrid quantum networks: We have taken first steps towards coupling broad band (e.g. quantum dot) photons to narrow band fiber coupled atomic memories. Quantum networks will have to rely on so called quantum repeaters for large scale distribution of quantum states. Quantum repeaters remain an enormous challenge for experimenters. With quantum walks – i. e. driven discrete transport on a lattice conditioned on the spin state – we operate a tool realizing controlled coherent transport of atoms over tens of lattice sites – up to the so called quantum speed limit available. I will present the experimental realization of “ideal negative measurements” showing strong violation of the LeggettGard inequality. The experiment distinguishes quantitatively the macro realist’s world from the quantum world. A few more examples including e.g. the creation of artificial magnetic fields will be given. The ultimate aim of these experiments is the creation of quantum cellular automata. 
13:45, ENS – 24, rue Lhomond – 75005 Paris, Room : IV 
15/03/2019  Allard Mosk Utrecht University 
Speckle correlations and Image information in turbid media
Random scattering of light, which takes place in paper, paint and biological tissue is an obstacle to imaging and focusing of light and thus hampers many applications. At the same time scattering is a phenomenon of basic physical interest as it allows the study of fascinating interference effects such as open transport channels, which enable lossless transport of waves through strongly scattering materials. These speckle correlation effects are associated with a relatively broad bandwidth, raising the question whether they are associated with light that has undergone a lessthan average number of scattering events. 
13:45, Collège de France – 11, place MarcelinBerthelot – 75005 Paris, Room : 2 
12/02/2019  Thomas Udem MaxPlanck Garching 
Precision Spectroscopy of Atomic Hydrogen and the Proton Radius Puzzle
Precise determination of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state with a natural line width of only 1.3 Hz. Its transition frequency has been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference [1]. A measurement of the Lamb shift in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct [2]. In order to shed light on this discrepancy the transition frequency of one of the broader lines in atomic hydrogen has to be measured with very good accuracy. For this purpose we have employed our previous 1S2S apparatus as a cold source of laser excited 2S atoms in order to perform spectroscopy on the 2S4P transitions. With a natural line width of 12.7 MHz, large Doppler effects, quantum interference etc. a good line shape analysis is mandatory to identify the true transition frequency. Our result on this transition yields a value for the proton radius that is compatible with the value obtained from muonic hydrogen with an uncertainty that is comparable to the previous hydrogen world data [3]. Meanwhile Helene Fleurbaey and her team at the Laboratoire Kastler Brossel, Paris have remeasured the 1S3S transition frequency with a significantly improved accuracy and find the previous “regular hydrogen charge radius” [4]. At our lab we have also been working on this transition with a different method. We hope to be ready to report a result soon. This will provide a unique opportunity to compare two highly accurate measurements obtained at different labs. References C. G. Parthey et al., Phys. Rev. Lett. 107, 203001 (2011) 
13:45, ENS – CONF IV – 24, rue Lhomond – 75005 Paris 
Date  Speaker  Title and abstract  Time and location 
10/12/2018  Pertti Hakonen Aalto University 
Josephson effect in suspended singlewalled carbon nanotubes
We study suspended, 300nmlong singlewalled carbon nanotubes (SWCNT) contacted using MoRe leads. Good contact transparency of the superconductornanotube interface allows for the observation of proximityinduced superconductivity in our SWCNT devices. The magnitude of the switching supercurrent ranges up to 50 nA and can be tuned periodically by gateinduced charge. The gate charge modulates the retrapping current even more strongly, and its magnitude becomes vanishingly small far away from the charge degeneracy point. Under rf irradiation, our SWCNT devices display clear Shapiro steps, the shape of which depend on the rf frequency and power. Under certain conditions the observed steps become hysteretic, indicating small dissipation on the Josephson phase dynamics at the rf frequency. In these SWCNT devices we find mechanical resonances around 1.5 GHz, while the Q factors amount up to 15000 near the charge degeneracy point. Mechanical modes can be observed also in the superconducting regime either by mixing by the currentphase relation or by inducing Shapiro steps resonantly with the mechanical mode, which both reflect the interplay between the Josephson dynamics and the mechanical degrees of freedom. In addition, we find bifurcation of Shapiro steps around the mechanical resonance frequency, both at fundamental and subharmonic resonance drives. The understanding of these phenomena within the framework of current biased RCSJ model will be discussed. 
11:00, Jussieu – Amphi Herpin (Bâtiment Esclangon) 
10/10/2018  Serge Reynaud Laboratoire Kastler Brossel 
Métrologie quantique et relativité
La métrologie moderne est basée sur la physique quantique et la relativité. La seconde est définie comme un nombre entier de périodes d’une transition atomique et le mètre est déduit de la valeur fixée pour la vitesse de la lumière dans le vide. Très prochainement, la constante de Planck et la charge élémentaire vont être fixées avec des valeurs exactes qui remplaceront les anciennes définitions du kilogramme et de l’ampère. Le nouveau SI va réaliser le programme d’universalité des unités engagé lors de la création du système métrique. Il pose aussi des questions nouvelles à l’interface entre physique quantique, relativité et métrologie. On discutera ces questions et on présentera une esquisse de cadre théorique où des observables sont définies pour le temps, l’espace et la masse de manière à être compatibles avec les exigences relativistes et quantiques. 
13:45, Jussieu – Tour 13/23, salle 210 
09/10/2018  Vincent Debierre Max Planck Institute of Heidelberg 
Hydrogenlike systems from low to highZ: van der Waals interactions and the bound electron gfactor
We present theoretical results on hydrogen atoms and hydrogenlike ions. 
13:45, Jussieu – Tour 13/23, salle 210 
26/09/2018  Holger Müller UC Berkeley Physics 
Measurement of the fine structure constant as test of the standard model
Measurements of the finestructure constant are powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium133 atoms in a matterwave interferometer, we recorded a measurement of the finestructure constant α = 1/137.035999046(27) at 0.20 parts per billion accuracy using multiphoton interactions such as Bragg diffraction and Bloch oscillations. Comparison with Penning trap measurements of the electron gyromagnetic anomaly via the Standard Model of particle physics has implications for darksector candidates and electron substructure. We will close with an outlook on future applications of matterwave interferometry. 
13:45, Jussieu – Tour 13/23, salle 210 
21/09/2018  Edward Hinds Imperial College London 
Magnetooptical trapping and subDoppler cooling of molecules
Atomic physics has been revolutionised by the introduction of laser techniques to cool atoms far below the Doppler limit. Now, it has become possible to laser cool molecules, to collect them in a magnetooptical trap, to cool them below the Doppler limit [1,2] and to trap them with modest magnetic fields [3]. These ultracold molecules open up a wide vista of future applications. To give a few examples, they can be optically or magnetically trapped to form arrays for quantum simulation, they can make a molecular fountain for testing fundamental physics at unprecedented levels of sensitivity, and they open a new energy range for the study of ultracold collisions and ultracold chemistry. I will review the current status of this field. 
13:45, Collège de France Salle 5 
19/09/2018  Nir Davidson Weizmann Institute of Science Israel 
Optomechanical strain and anomalous dynamics with trapped atoms
We report the observation of the optomechanical strain applied to ultracold rubidium atoms when shined on by an intense, far detuned homogenous laser beam. This force acts perpendicular to the laser beams direction and depends on the atomic cloud density profile, effectively generating interactions between the atoms. We refer to this force as electrostriction, since it resembles shape changes of materials under the application of a static electric field. We experimentally demonstrate the basic features of electrostriction, distinguishing it from the wellestablished scattering and dipole forces, and proving it is a new type of force [1]. We also report on experimental study the anomalous realspace and phasespace dynamics of ultracold atoms in a one dimension where the spatial distribution exhibits fractional selfsimilarity and Lévy statistics [2]. We show that the positionvelocity correlation function builds up on a timescale related to the initial conditions of the ensemble and then decays asymptotically as a powerlaw, following a simple scaling theory involving the powerlaw asymptotic dynamics of position and velocity [3]. Finally, for trapped atoms we demonstrate a breakdown of equipartition theorem [4] predicted for anomalous dynamics in [5]. 1. N. Matzliah, H. Edri, A. Sinay, R. Ozeri, and N. Davidson, Phys. Rev. Lett. 119, 163201 (2017). 2. Y. Sagi, M. Brook, I. Almog, and N. Davidson, Phys. Rev. Lett. 108, 093002 (2012). 3. G. Afek, J. Coslovsky, A. Courvoisier, O. Livneh, and N. Davidson, Phys. Rev. Lett. 119, 060602 (2017). 4. G. Afek, A. Courvoisier, A. Cheplev, and N. Davidson, submitted. 5. Dechant, D. Kessler, and E. Barkai, Phys. Rev. Lett. 115, 173006 (2015). 
13:45, Collège de France – Bât. A, RDC – Salle 2 
12/09/2018  Patrick Dupré Laboratoire de PhysicoChimie de l’Atmosphère 
Frequency Modulation Spectroscopy in Cavity, Challenging the Precision and the Sensitivity: Application to HD
The contemporary spectroscopy of gas targets several objectives, such as the fine description of the molecular Hamiltonians, the trace detection of diverse species, and the fundamental physics. In simple molecules such as molecular hydrogen, the transitions between energy levels can be probed to test the Standard Model of the Physics (i.e., the Quantum ElectroDynamics), and beyond. For example, the protontoelectron mass ratio and the protonradius size can be challenged. On other side, the detection of trace of molecules is of crucial importance for understanding chemical processes and molecular line shape. Uptodate spectroscopy techniques based on optical cavities associated with Optical Frequency Combs have been developed in the NearInfrared range to challenge sensitivity and frequency precision. We will illustrate the capability of the NoiseImmune CavityEnhanced Optical Heterodyne Molecular Spectroscopy (NICEOHMS), from both theoretical and experimental approaches. Very recent results on a few molecular species (C2H2 and HD) will be discussed for questioning the ultimate resolution and sensitivity which can be targeted. 
13:45, Jussieu tour 1323 2ème étage. 
Date  Speaker  Title and abstract  Time and location 
19/07/2018  E WU (East China Normal University, Shanghai) 
Highefficiency broadband singlephoton frequency upconversion
Nowadays, singlephoton frequency upconversion detectors (UCDs) have recently drawn a great deal of attention because it can be utilized as a quantum interface that enable qubits to transfer from infrared to visible regime, while preserving the quantum state information and then use SiAPDs to count the visible sumfrequency replicas of the infrared photons with high detection efficiency, high signaltonoise ratio, short dead time, low timing jitter. The UCDs are increasingly used in more fields of importance, such as quantum key distribution (QKD), quantum metrology, quantum computation and quantum tomography. However, when pulse duration of the signal photons are very short to femtosecond where the spectrum of signal photons is very broadband to fulfill the Fourier transformation, the conversion efficiency will be much decreased, because the spectral width from these source is much wider than the acceptance bandwidth of the PPLN waveguide (0.2 nm). Here, we demonstrated a high efficiency telecom wavelength broadband singlephoton frequency upconversion in PPLN crystal. By optimizing the pump light spectral bandwidth, we got 19.54 % conversion efficiency with a signal spectral bandwidth of 7.9 nm. 
13:45, Jussieu tour 1323 2ème étage. 
28/06/2018  Lincoln Carr (Colorado School of Mines) 
Manybody quantum chaos of ultracold atoms in a quantum ratchet
There are now over 200 quantum simulators on at least 8 separate architectures with long coherence times and controlled dynamics. These experimental systems have generated tremendous excitement about driven interacting quantum systems resulting in physics ranging from time crystals to dynamical manybody localization. The quantum ratchet adds a new feature to periodic driving: a preferred direction in both time and space, i.e., parity and timereversal symmetrybreaking. By studying weakly interacting ultracold bosons in a quantum ratchet on a ring in position, momentum, and Floquet representations, we demonstrate the limits of known measures of quantum chaos in a system with a clearly defined and rather famous semiclassical or meanfield limit, and moreover supporting experiments. We show that the usual WignerDyson statistics used to identify chaos are smeared out as we couple nonresonant modes into the drive. In contrast, the entropy of entanglement, condensate depletion, and inverse participation ratio all serve as accurate alternate identifiers for the chaotic regime in which the current on the ring flipflops with a positive Lyapunov exponent in the meanfield limit. The dimension of the strange attractor is found to depend on the local vs. global nature of the observables. Moreover, the growth of depletion indicates mean field theory breaks down at realistic experimental times scaling polynomially as in the chaotic regime. This study opens the door to beyond singlefrequency manybody Floquet physics showing many surprises and subtleties in both the quantum manybody dynamics and the meanfield limit (or lack thereof). Our prediction of a concrete time at which depletion grows is experimentally observable via an interference experiment. The dynamics and emergent structure of higher order correlators remains an especially intriguing avenue of exploration as we find that, contrary to oftstated popular opinion, chaos, at least in the quantum ratchet, does not lead to high entanglement. 
13:45, Jussieu tour 1323 2ème étage. 
21/06/2018  Jook Walraven (Univ. of Amsterdam) 
Ultrafast manybody interferometry of impurities coupled to a Fermi sea
The fastest possible collective response of a quantum manybody system is related to its excitations at the highest possible energy. In condensed matter systems, the time scale for such “ultrafast” processes is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we observed nonequilibrium dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the nonperturbative quantum evolution of a fermionic manybody system, revealing in real time the formation dynamics of quasiparticles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast timedomain methods applied to strongly interacting quantum gases enable the study of the dynamics of quantum matter under extreme nonequilibrium conditions. 
13:45, Collège de France, salle 5 
17/05/2018  Aephraim Steinberg (Uni. of Toronto) 
Comment compter un photon unique, et trouver un résultat de 1000 : d’étranges conséquences de la mesure quantique, à l’aide d’atomes froids
Je présenterai nos travaux expérimentaux concernant les mesures quantiques faites sur des systèmes postsélectionnés. Notamment, nous nous servons d’atomes froids et de l’effet «EIT» pour créer des interactions photonphoton suffisamment puissantes qu’on observe la phase nonlinéaire imprimée par des impulsions au niveau du photon unique sur un fasiceau sonde. En s’appuyant sur le formalisme de «weak measurement» de Yakir Aharonov et al., nous montrons aussi que quand la mesure est effectuée sur un photon postsélectionné dans un état final donné, l’effet sur la sonde peut être «amplifié», de sorte qu’une mesure du nombre de photons dans une région d’espace peut même dépasser le nombre de photons total. 
13:45, Jussieu, salle 210 couloir 1323 
04/04/2018  Aaron Tranter (ANU, Australia) 
Deep learning cold atomic ensembles for quantum memories
Quantum memories are integral to the realization of quantum information networks and quantum information processing. A promising platform is gradient echo memory (GEM) in cold atomic systems with demonstrated efficiencies of ~87%. We demonstrate the first application of a deep learning algorithm to a cold atomic system in order to increase the optical depth (OD) of our atomic trap and thus increase memory efficiency. We perform a 63 parameter optimisation and find solutions that are agnostic to considerations regarding monotonicity or continuity and vastly outperform human solutions increasing our optical depth by (81+3)%. We also observe a physical change in the atomic cloud corresponding to the spatial distribution of the atomic ensemble and apply the optimisation to the GEM protocol. 
13:45, Jussieu, salle 210 couloir 1323 
21/03/2018  Denis Vasilyev (IQOQI Innsbruck) 
A Quantum Scanning Microscope for Cold Atoms and an overview of a ‘FewAtom’ Quantum Optical Antenna
I will present my recent work made in IQOQI. The main part of the talk is devoted to the quantum scanning microscope arXiv:1709.01530 (to be published in PRL) We propose and analyze a scanning microscope to monitor `live’ the quantum dynamics of cold atoms in a Cavity QED setup. The microscope measures the atomic density with subwavelength resolution via dispersive couplings to a cavity and homodyne detection within the framework of continuous measurement theory. We analyze two modes of operation. First, for a fixed focal point the microscope records the wave packet dynamics of atoms with time resolution set by the cavity lifetime. Second, a spatial scan of the microscope acts to map out the spatial density of stationary quantum states. Remarkably, in the latter case, for a good cavity limit, the microscope becomes an effective quantum nondemolition (QND) device, such that the spatial distribution of motional eigenstates can be measured backaction free in single scans, as an emergent QND measurement. In the final part of the talk I will present an overview of our ongoing work involving cold Rydberg atoms in regular arrays forming an optical antenna arXiv:1802.05592 We describe the design of an artificial `free space’ 1Datom for quantum optics, where we implement an effective twolevel atom in a 3D optical environment with a chiral lightatom interface, i.e. absorption and spontaneous emission of light is essentially unidirectional. This is achieved by coupling the atom of interest in a laserassisted process to a `fewatom’ array of emitters with subwavelength spacing, which acts as a phasedarray optical antenna. We develop a general quantum optical model based on WignerWeisskopf theory, and quantify the directionality of spontaneous emission in terms of a Purcell $\beta$factor for a given Gaussian (paraxial) mode of the radiation field, predicting values rapidly approaching unity for `fewatom’ antennas in bi and multilayer configurations. Our setup has for neutral atoms a natural implementation with laserassisted Rydberg interactions, and we present a study of directionality of emission from a string of trapped ions with superwavelength spacing. 
13:45, ENS, salle Conf IV 
07/02/2018  Nouveaux doctorants et postdocs (LKB) 
Présentations des nouveaux arrivants du LKB
Jour II 
14:00, CdF, salle 5 
13/12/2017  Igor Mekhov (SPEC CEA, St. Petersburg State University, University of Oxford) 
Weak measurements and quantum optical lattices for strongly correlated bosons and fermions While optical lattices are wellestablished systems, the quantum nature of light is neglected in all setups so far. We show theoretically that the light quantization significantly broadens the range of physical phenomena. We prove that the quantum backaction of weak global measurement constitutes a novel source of competitions in manybody systems. This leads to novel effects beyond physics of open dissipative systems: multimode oscillations of macroscopic superposition states, protection and breakup of fermion pairs, as well as generation of antiferromagnetic states. Novel processes beyond standard Hubbard models can be designed by the measurement, entering the field of nonHermitian manybody physics: longrange correlated pair tunnelling and Ramanlike secondorder transitions beyond typical quantum Zeno dynamics. We demonstrate the generation of multipartite mode entanglement and feedback control of manybody states out of reach of dissipative phase transitions.Quantization of optical lattice potentials enables quantum simulations of various longrange interacting systems unobtainable using classical optical lattices. This leads to new quantum phases (dimers, trimers, etc. of matter waves similar to valence bond solids) different from density orders (e.g. supersolids and density waves) directly benefiting from the collective lightmatter interaction. 
13:45, ENS, conf IV 
17/01/2018  Nouveaux doctorants et postdocs (LKB) 
Présentations des nouveaux arrivants du LKB
Jour I 
14:00, CdF, salle 2 
13/12/2017  Mark Kasevich (Stanford) 
Quantum measurement strategies for atoms, photons and electrons Quantum measurement protocols based on dispersive cavityassisted interactions will be described. We will show how these protocols lead to performance improvements for precision atomic sensors and to new tests of quantum mechanics. We will also describe quantum imaging methods based on repeated coherent interactions in degenerate optical and electron cavities. 
13:45, CdF, salle 2 
06/12/2017  Serge Reynaud (LKB) with collaboration MICROSCOPE 
Premiers résultats de MICROSCOPE Les premiers résultats du satellite MICROSCOPE démontrent avec une précision améliorée que les corps tombent de façon universelle dans le vide. Il s’agit d’une nouvelle confirmation de la relativité générale proposée par Albert Einstein il y a plus d’un siècle et qui a été encore vérifiée récemment par la détection des ondes gravitationnelles. MICROSCOPE (Microsatellite à trainée compensée pour l’observation du principe d’équivalence) a été lancé le 25 avril 2016. L’analyse des premières mesures scientifiques effectuées améliore la précision du test du principe d’équivalence au niveau inégalé de 2.1014. Ce résultat repousse les limites d’une éventuelle violation du principe d’équivalence d’un facteur 10 et apporte de nouvelles contraintes aux théories d’extension de la relativité générale. Les autres données déjà acquises, ou à collecter d’ici la fin de la mission au printemps 2018, amélioreront encore cette précision pour se rapprocher de l’objectif de 1015.The MICROSCOPE mission: first results of a space test of the Equivalence Principle Pierre Touboul et al. Phys. Rev. Lett. 119, 231101 (2017) 
13:45, ENS, salle L363/L365 
22/11/2017  Dmitry Petrov (LPTMS, Univ ParisSud) 
Mesoscopic fewbody problem with shortrange interactions
I will describe our work with Betzalel Bazak on the N+1body fermionic problem in three dimensions [1] and Nboson problem in two dimensions [2]. By developing a new method of solving fewbody integral equations we are able to obtain precise results for ground state energies. In particular, we predict a universal pentamer state and fivebody Efimov effect for the 4+1 fermionic problem and quantify the fewtomanybody crossover for twodimensional bosons. I point to Refs. [3] and [4] as a recommended reading. [1] B. Bazak and D.S. Petrov, « Fivebody Efimov effect and universal pentamer in fermionic mixtures », Phys. Rev. Lett. 118, 083002 (2017) [2] B. Bazak and D.S. Petrov, « Energy of N twodimensional bosons with zerorange interactions », arXiv:1711.02345 [3] Y. Castin, C. Mora, and L. Pricoupenko, « FourBody Efimov Effect for Three Fermions and a Lighter Particle », Phys. Rev. Lett. 105, 223201 (2010) [4] H.W. Hammer and D. T. Son, « Universal Properties of TwoDimensional Boson Droplets », Phys. Rev. Lett. 93, 250408 (2004) 
13:45, CdF, salle 2 
25/10/2017  Juan Pablo Paz (Université de Buenos Aires) 
Using a Quantum Work Meter to test non equilibrium fluctuation theorems The so called « fluctuation theorems » are one of the most important results in non equilibrium thermodynamics obtained during the last decades. They connect the behavior of a system evolving far away from equilibrium with certain properties of thermal equilibrium states of the same system. The work probability distribution plays a major role in such theorems and its measurement attracted a lot of interest recently. In this talk I will review a new strategy for measuring work on a quantum system which evolves out of equilibrium. I will also show how these ideas have been recently implemented in an experiment which enabled us to directly sample the work probability distribution. The « quantum work meter » I will present, built with an ensemble of cold Rubidium atoms manipulated by an atom chip, enabled us to perform a direct test of the most notable fluctuation theorem: the Jarzynski identity. 
14:00, CdF, salle 2 
05/10/2017  Serge Reynaud (LKB) 
Métrologie quantique et symétries relativistes La métrologie moderne est basée sur la physique quantique et relativiste. La seconde est définie comme un nombre entier de périodes d’une horloge atomique et le mètre est dérivé de la valeur fixée pour la vitesse de la lumière dans le vide. Bientôt, la constante de Planck et la charge élémentaire devraient être également définies avec des valeurs exactes remplaçant les anciennes définitions du kilogramme et de l’ampère. Le statut quantique des observables associées au temps, à l’espace, à la masse, leur compatibilité avec les symétries relativistes restent pourtant des questions ouvertes. On discutera d’abord de manière qualitative ces questions à l’interface entre métrologie, physique quantique et relativité. On présentera ensuite un cadre théorique où les observables sont définies de manière à être compatibles à la fois avec les exigences relativistes et quantiques. Dans cette approche, la masse observable n’est plus une constante, comme on peut le deviner en raison de sa dimension par rapport à la dilatation. Les transformations des observables vers des référentiels accélérés diffèrent de leurs homologues classiques. Les symétries relativistes permettent néanmoins d’étendre les règles de covariance de la relativité, ce qui conduit à une version quantique du principe d’équivalence d’Einstein identifié à la transformation de la masse observable. 
11:00, Danjon (Paris) 
Date  Speaker  Title and abstract  Time and location 
21/06/2017  Raphael Lopes (Cambridge) 
On strongly interacting homogeneous Bose—Einstein condensates During this talk, I will show that using twophoton Bragg spectroscopy, one can study the energy of particlelike excitations in a strongly interacting homogeneous BoseEinstein condensate, and observe dramatic deviations from Bogoliubov theory. In particular, at large scattering length a the shift of the excitation resonance from the freeparticle energy changes sign from positive to negative. For an excitation with wavenumber q, this sign change occurs at a about 4/(\pi q), in agreement with the Feynman energy relation and the static structure factor expressed in terms of the twobody contact. For a about 3/q we also see a breakdown of this theory, and better agreement with calculations based on the Wilson operator product expansion. Neither theory explains our observations across all interaction regimes, inviting further theoretical efforts.Moreover, we also show that through the use of a Bragg filtering method one can access the momentum distribution of an ultracold atomic gas and extract its condensed fraction. We observe that the condensed fraction reduces linearly as a function of (na^3)^0.5, behaviour which follows the quantitative prediction of quantum depletion introduced by N. N. Bogoliubov 70 years ago. 
13:45, CdF, salle 5 
15/03/2017  Joseph H. Thywissen (University of Toronto) 
Spin transport in 3D and 2D strongly interacting Fermi gases Transport in strongly interacting systems is a topic of broad interest to physicists, studied in materials, fluids, cold atoms, and even in theories using holographic duality. Here we study spin transport in the demagnetization dynamics of a strongly interacting ultracold Fermi gas. Atoms are initialized in a superposition of two internal states, creating a transverse magnetization that decays in the presence of a magnetic field gradient. We observe the ensembleaveraged magnetization with a spinecho sequence, and measure twobody correlations (the contact) with timeresolved rf spectroscopy.In the strongly interacting regime, the dynamics are found to be diffusive. The spin diffusivity reaches a lower bound, roughly 2 hbar/m (where m is the bare mass of the potassium 40 atoms used here), when interactions are tuned to unitarity. We also find a reactive component to dynamics, due to the spinrotation effect, where the spin current precesses around the local magnetization. Finally, we compare dynamics in three and twodimensional gases. Our work supports the conjecture of an upper bound on the rate of relaxation to local equilibrium. 
13:45, ENS, salle Conf IV 
15/02/2017  Wonho Jhe (Seoul National University) 
Nonlinear, Nonequilibrium, Collective Dynamics in a Periodically Modulated Cold Atom System Periodically modulated systems form one of the most important classes of nonequilibrium systems, both conceptually and in terms of applications. They have discrete timetranslation symmetry: they are invariant with respect to time translation by modulation period tF. Nevertheless, they have stable vibrational states with periods of 2tF, that is period doubling. Interestingly, in a manybody system, dynamical period doubling in itself does not break the time translation symmetry, a consequence of fluctuations. However, if as a result of the interaction the state populations become different, the symmetry is broken, an Isingclass phase transition. We show that an atomic system in a periodically modulated optical trap displays an ideal meanfield symmetrybreaking transition, which is a critical phenomenon as demonstrated by experimental measurement of critical exponents. We also discuss the dynamic phase transition as well as kinetic phase transition observed in the modulated atom trap. 
13:45, CdF, salle 2 
01/02/2017  Jürgen Volz (VCQ, Vienne) 
Quantum optical nonreciprocal devices based on chiral interaction of light and matter Micro and nanophotonic components such as optical nanofibers confine light at the wavelength scale and enable the control of its flow in integrated optical environments. The strong confinement of light leads to an inherent link between its local polarization and propagation direction – the light obtains a chiral character. This fundamentally alters the physics of lightmatter interaction and gives rise to phenomena such as highly directional spontaneous emission and directiondependent coupling strengths [1].In my talk I will introduce the underlying principles of this chiral lightmatter interaction. Then I will present how we employ this effect to realize lowloss nonreciprocal transmission of light at the singlephoton level through a silica nanofiber [2]. We use two experimental approaches where an ensemble of spinpolarized atoms is weakly coupled to the nanofiberguided mode or a single spinpolarized atom is strongly coupled to the nanofiber via a whisperinggallerymode resonator. We observe a strong imbalance between the transmissions in forward and reverse direction of about 10 dB for both systems while, at the same time, the forward transmissions still exceed 70%.By interfacing a whisperinggallerymode resonator with two nanofibers we extended this system to a 4port device, where a single atom routes photons nonreciprocally from one fiber port to the next, thus realizing a quantum optical circulator [3]. The demonstrated systems exemplify a new class of nanophotonic devices based on chiral lightmatter interaction. Since their operation direction can be controlled by individual quantum emitters, such devices could even be prepared in a superposition of their operational modes which allows their integration in future quantum information processing and quantum simulation experiments.[1] P. Lodahl et al., arXiv:1608.00446 (2016)[2] C. Sayrin et al., Phys. Rev. X 5, 041036 (2015)3] M. Scheucher et al., Science 354, 1577 (2016) 
13:45, CdF, salle 2 
25/01/2017  Nicolas Joly (MPI, Erlangen) 
Génération de sources non classiques au moyen de fibres microstructurées Les fibres microstructurées sont un excellent outil pour l’optique non linéaire en raison de la possibilité de contrôler et modeler leurs propriétés de dispersion et leur non linéarité. Dans ce séminaire je présenterai différentes fibres dédiées à la génération d’états non classiques de la lumière. Dans un premier temps je montrerai la création de faisceaux jumeaux corrélés, créés par instabilité modulationelle. Le système est particulièrement simple et versatile et se compose d’une fibre à cœur creux remplie d’argon gazeux pompée par un laser saphirtitane. L’utilisation de gaz comme élément non linéaire permet de modifier à souhait la dispersion du système qui, une fois ajustée correctement, permet à des impulsions (300 fs) de développer des bandes latérales corrélées. De plus la source est spatialement monomode et présente un petit nombre de modes temporels (<5). Dans un deuxième temps, je présenterai un nouveau concept de fibre microstructurée permettant, en principe, la création d’état triplet. La génération d’état triplet, dans laquelle un photon donne spontanément naissance à trois photons, peut être considérée comme le processus inverse du triplement de fréquence et nécessite par conséquent les mêmes conditions d’accord de phase. La dispersion chromatique impose cependant l’utilisation de différents modes spatiaux, ce qui est techniquement délicat. Nous avons récemment proposé un concept de fibre présentant deux modes de guidance différents : aux grandes longueurs d’onde la guidance s’opère par réflexion totale alors que la troisième harmonique est guidée par effet de bande interdite. Les premières expériences montrent la possibilité d’un accord de phase entre deux modes fondamentaux. 
13:45, ENS, L357/L356 
18/01/2017  Nouveaux doctorants et postdocs (LKB) 
Présentations des nouveaux arrivants du LKB Jour II 
13:45, CdF, salle 5 
14/12/2016  Nouveaux doctorants et postdocs (LKB) 
Présentations des nouveaux arrivants du LKB Jour I 
11:00, CdF, salle 2 
30/11/2016  Franklyn Quinlan (NIST, USA) 
Optical to RF frequency generation with optical frequency combs
The most frequencystable electromagnetic radiation is now produced optically, with stable reference cavities demonstrating fractional frequency instabilities below 10^16 at 1 second and optical clocks reaching 10^18 at 10^4 seconds. This talk will cover recent work at NIST using optical frequency combs to transfer this stability across the optical domain at the level of 10^18 at 1 second, as well as into the RF, microwave, and mmwave domains at the level of 10^15 to 10^17 at 1 second. In addition to the optical frequency combs themselves, elements of compact ultrastable optical cavities, highspeed photodetection and broadband electronic synthesis will also be discussed. 
13:45, CdF, salle 2 
23/11/2016  Boris Svistunov (UMass Amherst, USA) 
Superfluidity and Topological Order
The decadeslong history of theoretical understanding of the phenomenon of superfludity—from the TiszaLandau phenomenology to the modern picture based on the emergence of topological constant of motion—has been most dramatic and instructive. Critically overviewing main historic steps highlights the crucial importance of the topological language for revealing the origin the phenomenon, as well as for establishing general relations of superfluid hydrodynamics, BerezinskiiKosterlitzThouless transition, and superfluidinsulator quantum phase transitions in one dimension. 
13:45, CdF, salle 5 
9/11/2016  Emmanuel Fort (Institut Langevin) 
Selfpropelled droplets: A ‘classical’ waveparticle duality based on time mirrors
We have recently discovered a macroscopic object composed of a material particle dynamically coupled to a wave packet. The particle is a droplet bouncing on the surface of a vertically vibrated liquid bath; its pilotwave is the result of the superposition of the surface waves it excites. Above an excitation threshold, this symbiotic object, designated as a “walker” becomes selfpropelled. 
13:45, CdF, salle 2 
26/10/2016  Giacomo Roati (University of Florence) 
Dynamics of strongly interacting atomic Fermi gases
I will present two antithetic experimental studies, exploiting strongly interacting ultracold Fermi gases of 6Li atoms confined in optical potentials. In a first experiment, we create the analogous of a Josephson junction by bisecting BECBCS crossover superfluids by a thin optical barrier. We observe coherent dynamics in both the population and in the relative phase between the two superfluid reservoirs. For critical parameters, we see how the Josephson dynamics is affected by the presence of topological defects entering the superfluid bulk [1]. In a second experiment, we create an artificial ferromagnetic state by segregating degenerate spin mixtures into two initially disconnected reservoirs [2]. We study the spin dynamics for different interaction strengths and temperatures. For sufficiently high values of the interspin repulsive interactions and sufficiently low temperatures, we observe a softening of the spin dipole mode and a timewindow during which spin diffusion is zeroed. Our measurements provide exciting new insights into the physics of attractive and repulsive Fermi gases. [1] G. Valtolina et al., Science 350, 1505 (2015) 
13:45, CdF, salle 5 
19/10/2016  Sebastian Will (Columbia University) 
Coherent Quantum Control of Ultracold Dipolar NaK Molecules
Ultracold molecules open up new routes for precision measurements, quantum information processing and manybody quantum physics. In particular, dipolar molecules with longrange interactions promise the creation of novel states of matter, such as topological superfluids and quantum crystals. Dipolar bialkali molecules can be efficiently assembled from ultracold atoms. Using this approach we have created the first neardegenerate gases of strongly dipolar NaK molecules. At temperatures of few hundred nanokelvin, we prepare ensembles, in which all molecules occupy the rovibrational and hyperfine ground state. 
13:45, CdF, salle 2 