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The monochromatic driving of a quantum system is a successful technique in quantum simulations, well captured by an effective Hamiltonian approach, and with applications in artificial gauge fields and topological engineering. Here, we investigate multichromatic Floquet driving for quantum simulation. Within a well-defined range of parameters, we show that the time coarse-grained dynamics of such a driven closed quantum system is encapsulated in an effective master equation for the time-averaged density matrix, that evolves under the action of an effective Hamiltonian and tunable Lindblad-type dissipation or quantum gain terms. As an application, we emulate the dissipation induced by phase noise and incoherent emission or absorption processes in the bichromatic driving of a two-level system, and reproduce the phase decoherence in a harmonic oscillator model.

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The wave nature of matter remains one of the most striking aspects of quantum mechanics. Since its inception, a wealth of experiments has demonstrated the interference, diffraction or scattering of massive particles. More recently, experiments with ever increasing control and resolution have allowed imaging the wavefunction of individual atoms. Here, we use quantum gas microscopy to image the in-situ spatial distribution of deterministically prepared single-atom wave packets as they expand in a plane. We achieve this by controllably projecting the expanding wavefunction onto the sites of a deep optical lattice and subsequently performing single-atom imaging. The protocol established here for imaging extended wave packets via quantum gas microscopy is readily applicable to the wavefunction of interacting many-body systems in continuous space, promising a direct access to their microscopic properties, including spatial correlation functions up to high order and large distances.

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Boltzmann showed that in spite of momentum and energy redistribution through collisions, a rarefied gas confined in a isotropic harmonic trapping potential does not reach equilibrium; it evolves instead into a breathing mode where density, velocity, and temperature oscillate. This counterintuitive prediction is upheld by cold atoms experiments. Yet, are the breathers eternal solutions of the dynamics even in an idealized and isolated system? We show by a combination of hydrodynamic arguments and molecular dynamics simulations that an original dissipative mechanism is at work, where the minute and often neglected bulk viscosity eventually thermalizes the system, which thus reaches equilibrium.

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Quantum optimal control is a set of methods for designing time-varying electromagnetic fields to perform operations in quantum technologies. This tutorial paper introduces the basic elements of this theory based on the Pontryagin maximum principle, in a physicist-friendly way. An analogy with classical Lagrangian and Hamiltonian mechanics is proposed to present the main results used in this field. Emphasis is placed on the different numerical algorithms to solve a quantum optimal control problem. Several examples ranging from the control of two-level quantum systems to that of Bose-Einstein Condensates (BEC) in a one-dimensional optical lattice are studied in detail, using both analytical and numerical methods. Codes based on shooting method and gradient-based algorithms are provided. The connection between optimal processes and the quantum speed limit is also discussed in two-level quantum systems. In the case of BEC, the experimental implementation of optimal control protocols is described, both for two-level and many-level cases, with the current constraints and limitations of such platforms. This presentation is illustrated by the corresponding experimental results.

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Sujets

Quantum collisions Nano-lithography Electromagnetic field Matter wave Chaos Piège magnéto-optique à miroir Cold atoms Bose Einstein Condensation Atomic beam Matter waves Optique atomique Plasmon polariton de surface Current Masques matériels nanométriques Condensat de Bose-Einstein Field equations stochastic Effet tunnel Entropy production Levitodynamics Engineering Mirror-magneto-optical trap Optical molasses Hamiltonian Quantum Maxwell's demon Théorie de Floquet Optical Atom optics Césium Ouvertures métalliques sub-longueur d'onde Physique quantique Gaz quantique Optical tweezers Condensat Bose-Einstein Condensats de Bose– Einstein Quantum chaos Effet tunnel assisté par le chaos Mechanics Atomes froids Effet rochet Condensats de Bose Einstein Condensats de Bose-Einstein Bose-Einstein condensates Fluorescence microscopy Bose-Einstein Approximation semi-classique et variationnelle Chaos-assisted tunneling Chaos quantique Espace des phases Bose-Einstein condensate Effet tunnel dynamique Ultracold atoms Bose-Einstein condensates Coherent control Cold atoms and matter waves Cold gases in optical lattices Bose–Einstein condensates Contrôle optimal Initial state Réseaux optiques Bose-Einstein Condensates Collisions ultrafroides Atom laser Experimental results Beam splitter Jet atomique Floquet theory Phase space Lentille de Fresnel Time dependence Optical lattice Non-adiabatic regime Optical lattices Bragg Diffraction Contrôle optimal quantique Nano-lithographie Fresnel lens Mélasse optique Constraint Fluid Puce atomique Condensation Bose-Einstein Condensate Atomes ultrafroids dans un réseau optique Condensation de bose-Einstein Couches mono-moléculaire auto assemblées Réseau optique Bragg scattering Periodic potentials Quantum optimal control Gaz quantiques Microscopie de fluorescence Optimal control theory Dynamical tunneling Lattice Diffraction de Bragg Atom chip Quantum control Onde de matière Numerical methods Bose Einstein condensate Dimension

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44

Nombre de notices déposées

79