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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.
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.
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.
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.
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