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Search Results: 1 - 10 of 8352 matches for " Fran?ois Impens "
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Hidden symmetry and nonlinear paraxial atom optics
Franois Impens
Physics , 2009, DOI: 10.1103/PhysRevA.80.063617
Abstract: A hidden symmetry of the nonlinear wave equation is exploited to analyse the propagation of paraxial and uniform atom-laser beams in time-independent, quadratic and cylindrical potentials varying smoothly along the propagation axis. The quality factor and the paraxial ABCD formalism are generalized to account exactly for mean-field interaction effects in such beams. Using an approach based on moments, these theoretical tools provide a very simple and yet exact picture of the interacting beam profile evolution. Guided atom laser experiments are discussed. This treatment addresses simultaneously optical and atomic beams in a unified manner, exploiting the formal analogy between nonlinear optics and nonlinear paraxial atom optics.
Quality factor of a matter-wave beam
Franois Impens
Physics , 2010, DOI: 10.1103/PhysRevA.77.013619
Abstract: Imperfections in dilute atomic beams propagating in the paraxial regime and in potentials of cylindrical symmetry have been characterized experimentally through the measurement of a parameter analogous to a beam quality factor [Riou et al., Phys. Rev. Lett. 96, 070404 (2006)]. We propose a generalization of this parameter, which is suitable to describe dilute matter waves propagating beyond the paraxial regime and in fully general linear atom-optical systems. The presented quality factor shows that the atomic beam symmetry can be traded for a better transverse collimation.
Classical phase-space approach for coherent matter waves
Franois Impens,David Guéry-Odelin
Physics , 2010, DOI: 10.1103/PhysRevA.81.065602
Abstract: We investigate a classical phase-space approach of matter-wave propagation based on the Truncated Wigner Equation (TWE). We show that such description is suitable for ideal matter waves in quadratic time-dependent confinement as well as for harmonically trapped Bose Einstein condensates in the Thomas-Fermi regime. In arbitrary interacting regimes, the TWE combined with the moment method yields the low-energy spectrum of a condensate as predicted by independent variational methods. TWE also gives the right breathing mode frequency for long-ranged interactions decaying as $1/r^2$ in 3D and for a contact potential in 2D. Quantum signatures, beyond the TWE, may only be found in the condensate dynamics beyond the regimes of classical phase-space propagation identified here.
The theory of quantum levitators
Franois Impens,Franck Pereira Dos Santos,Christian J. Bordé
Physics , 2011, DOI: 10.1088/1367-2630/13/6/065024
Abstract: We develop a unified theory for clocks and gravimeters using the interferences of multiple atomic waves put in levitation by traveling light pulses. Inspired by optical methods, we exhibit a propagation invariant, which enables to derive analytically the wave function of the sample scattering on the light pulse sequence. A complete characterization of the device sensitivity with respect to frequency or to acceleration measurements is obtained. These results agree with previous numerical simulations and confirm the conjecture of sensitivity improvement through multiple atomic wave interferences. A realistic experimental implementation for such clock architecture is discussed.
Non-additive dynamical Casimir atomic phases
Franois Impens,Claudio Ccapa Ttira,Paulo A. Maia Neto
Physics , 2013, DOI: 10.1088/0953-4075/46/24/245503
Abstract: We discuss a fundamental property of open quantum systems: the quantum phases associated with their dynamical evolution are non-additive. We develop our argument by considering a multiple-path atom interferometer in the vicinity of a perfectly conducting plate. The coupling with the environment induces dynamical corrections to the atomic phases. In the specific example of a Casimir interaction, these corrections reflect the interplay between field retardation effects and the external atomic motion. Non-local open-system Casimir phase corrections are shown to be non-additive, which follows directly from the unseparability of the influence functional describing the coupling of the atomic waves to their environment. This is an unprecedented feature in atom optics, which may be used in order to isolate non-local dynamical Casimir phases from the standard quasi-static Casimir contributions.
Dynamical local and non-local Casimir atomic phases
Franois Impens,Claudio Ccapa Ttira,Ryan O. Behunin,Paulo A. Maia Neto
Physics , 2014, DOI: 10.1103/PhysRevA.89.022516
Abstract: We develop an open-system dynamical theory of the Casimir interaction between coherent atomic waves and a material surface. The system --- the external atomic waves --- disturbs the environment --- the electromagnetic field and the atomic dipole degrees of freedom --- in a non- local manner by leaving footprints on distinct paths of the atom interferometer. This induces a non-local dynamical phase depending simultaneously on two distinct paths, beyond usual atom-optics methods, and comparable to the local dynamical phase corrections. Non-local and local atomic phase coherences are thus equally important to capture the interplay between the external atomic motion and the Casimir interaction. Such dynamical phases are obtained for finite-width wavepackets by developing a diagrammatic expansion of the disturbed environment quantum state.
Non-local double-path Casimir phase in atom interferometers
Franois Impens,Ryan O. Behunin,Claudio Ccapa Ttira,Paulo A. Maia Neto
Physics , 2012, DOI: 10.1209/0295-5075/101/60006
Abstract: We present a quantum open system theory of atom interferometers evolving in the quantized electromagnetic field bounded by an ideal conductor. Our treatment reveals an unprecedented feature of matter-wave propagation, namely the appearance of a non-local double-path phase coherence. Such a non-local phase arises from the coarse-graining over the quantized electromagnetic field and internal atomic degrees of freedom, yielding a non-Hamiltonian evolution of the atomic waves moving in presence of correlated quantum dipole and field fluctuations. We develop a diagrammatic interpretation of this phase, and estimate it for realistic experimental parameters.
Toward a test of angular momentum coherence in a twin-atom interferometer
Carlos R. de Carvalho,Ginette Jalbert,Franois Impens,J. Robert,Aline Medina,F. Zappa,N. V. de Castro Faria
Physics , 2014, DOI: 10.1209/0295-5075/110/50001
Abstract: We present a scheme well-suited to investigate quantitatively the angular momentum coherence of molecular fragments. Assuming that the dissociated molecule has a null total angular momentum, we investigate the propagation of the corresponding atomic fragments in the apparatus. We show that the envisioned interferometer enables one to distinguish unambiguously a spin-coherent from a spin-incoherent dissociation, as well as to estimate the purity of the angular momentum density matrix associated with the fragments. This setup, which may be seen as an atomic analogue of a twin-photon interferometer, can be used to investigate the suitability of molecule dissociation processes -- such as the metastable hydrogen atoms H($2^2 S$)-H($2^2 S$) dissociation - for coherent twin-atom optics.
Driving quantized vortices with quantum vacuum fluctuations
Franois Impens,Ana M. Contreras-Reyes,Paulo A. Maia Neto,Diego A. R. Dalvit,Romain Guérout,Astrid Lambrecht,Serge Reynaud
Physics , 2010, DOI: 10.1209/0295-5075/92/40010
Abstract: We propose to use a rotating corrugated material plate in order to stir, through the Casimir-Polder interaction, quantized vortices in an harmonically trapped Bose-Einstein condensate. The emergence of such vortices within the condensate cannot be explained with a computation of the Casimir-Polder potential based on the pairwise summation approach or on the proximity force approximation. It thus appears as a genuine signature of non-trivial geometry effects on the electromagnetic vacuum fluctuations, which fully exploits the superfluid nature of the sample. In order to discuss quantitatively the generation of Casimir-driven vortices, we derive an exact non-perturbative theory of the Casimir-Polder potential felt by the atoms in front of the grating. Our numerical results for a Rb condensate close to a Si grating show that the resulting quantum vacuum torque is strong enough to provide a contactless transfer of angular momentum to the condensate and generate quantized vortices under realistic experimental conditions at separation distances around $3$ microns.
The Changes in Cameroon’s Public Television in the Advent of Digital Switchover: The Impact of Technological Innovation on Audio-Visual Public Policies  [PDF]
Franois Wakata Bolvine
Advances in Journalism and Communication (AJC) , 2017, DOI: 10.4236/ajc.2017.51001
Abstract: Technological innovation strongly impacts the lives of citizens as a whole and is followed by serious consequences on national public policies and on the sector directly concerned. The dynamics of change in the national audio-visual landscape with the public service television engaged in the digital switch-over process is indeed the core of this study. It reveals how innovation has impelled policy-makers to develop a comprehensive strategy, leading to objectives and decisions to completely reshape the national audio-visual landscape with regard to legal, institutional, infrastructural, economic and cultural aspects; and, specifically, public television in its organization, functioning, mission as well as in its uses.
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