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Nicolas Cherroret

Publications and source records attributed to Nicolas Cherroret.

51 records · Page 3Linked to original sources
arXiv2017

Casimir-Polder force fluctuations as spatial probes of dissipation in metals

We study the spatial fluctuations of the Casimir-Polder force experienced by an atom or a small sphere moved above a metallic plate at fixed separation distance. We demonstrate that unlike the mean force, the magnitude of these fluctuations crucially relies on the relaxation of conduction electron in the metallic bulk, and even achieves values that differ by orders of magnitude depending on the amount of dissipation. We also discover that fluctuations suffer a spectacular decrease at large distances in the case of nonzero temperature.

quant-ph↗
arXiv2016

A self-consistent theory of localization in nonlinear random media

The self-consistent theory of localization is generalized to account for a weak quadratic nonlinear potential in the wave equation. For spreading wave packets, the theory predicts the destruction of Anderson localization by the nonlinearity and its replacement by algebraic subdiffusion, while classical diffusion remains unaffected. In 3D, this leads to the emergence of a subdiffusion-diffusion transition in place of the Anderson transition. The accuracy and the limitations of the theory are discussed.

cond-mat.dis-nn↗
arXiv2016

Induced dipole-dipole interactions in light diffusion from point dipoles

We develop a perturbative treatment of induced dipole-dipole interactions in the diffusive transport of electromagnetic waves through disordered atomic clouds. The approach is exact at order two in the atomic density and accounts for the vector character of light. It is applied to the calculation of the electromagnetic energy stored in the atomic cloud - which modifies the energy transport velocity - and of the light scattering and transport mean free paths. Results are compared to those obtained from a purely scalar model for light.

cond-mat.dis-nn↗
arXiv2016

Semiclassical spectral function and density of states in speckle potentials

We present a novel analytical method for calculating the spectral function and the density of states in speckle potentials, valid in the semiclassical regime. Our approach relies on stationary phase approximations, allowing us to describe the singular quantum corrections at low energies. We apply it to the calculation of the spectral function and the density of states in one and two-dimensional speckle potentials. By connecting our results with those of previous work valid in the high energy sector, we end up with a consistent description of the whole energy spectrum, in good agreement with numerical simulations.

cond-mat.dis-nn↗
arXiv2016

Return to the Origin as a Probe of Atomic Phase Coherence

We report on the observation of the coherent enhancement of the return probability ("enhanced return to the origin" , ERO) in a periodically kicked cold-atom gas. By submitting an atomic wave packet to a pulsed, periodically shifted laser standing wave, we induce an oscillation of ERO in time and explain it in terms of a periodic, reversible dephasing in the weak-localization interference sequences responsible for ERO. Monitoring the temporal decay of ERO, we exploit its quantum coherent nature to quantify the decoherence rate of the atomic system.

cond-mat.dis-nn↗
arXiv2016

Coherent backscattering reveals the Anderson transition

We develop an accurate finite-time scaling analysis of the angular width of the coherent backscattering (CBS) peak for waves propagating in 3D random media. Applying this method to ultracold atoms in optical speckle potentials, we show how to determine both the mobility edge and the critical exponent of the Anderson transition from the temporal behavior of the CBS width. Our method could be used in experiments to fully characterize the 3D Anderson transition.

cond-mat.dis-nn↗
arXiv2015

Statistical approach to Casimir-Polder potentials in heterogeneous media

We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere and a three-dimensional heterogeneous medium, by means of extensive numerical simulations based on the scattering theory of Casimir forces. The simulations allow us to confirm recent predictions for the mean and standard deviation of the Casimir potential, and give us access to its full distribution function in the limit of a dilute distribution of heterogeneities. These predictions are compared with a simple statistical model based on a pairwise summation of the individual contributions of the constituting elements of the medium.

quant-ph↗
arXiv2015

Thermalization of matter waves in speckle potentials

We show that the momentum distribution of a nonlinear matter wave suddenly released with a finite velocity in a speckle potential converges, after an out-of-equilibrium evolution, to a universal Rayleigh-Jeans thermal distribution. By exploring the complete phase diagram of the equilibrated wave, we discover that for low but nonzero values of the disorder strength, a large-scale structure -a condensate- appears in the equilibrium distribution.

cond-mat.dis-nn↗
arXiv2015

Fluctuations of the Casimir potential above a disordered medium

We study the statistical fluctuations of the Casimir potential felt by an atom approaching a dielectric disordered medium. Starting from a microscopic model for the disorder, we calculate the variance of potential fluctuations in the limit of a weak density of heterogeneities. We show that fluctuations are essentially governed by scattering of the radiation on a single heterogeneity, and discuss in which limits they become larger than the average value predicted by effective medium theory. Finally, for denser disorder we show that multiple scattering processes become relevant.

quant-ph↗
arXiv2014

How nonlinear interactions challenge the three-dimensional Anderson transition

In disordered systems, our present understanding of the Anderson transition is hampered by the possible presence of interactions between particles. We demonstrate that in boson gases, even weak interactions deeply alter the very nature of the Anderson transition. While there still exists a critical point in the system, below that point a novel phase appears, displaying a new critical exponent, subdiffusive transport and a breakdown of the one-parameter scaling description of Anderson localization.

cond-mat.dis-nn↗
arXiv2013

Backscattering echo of correlated wave packets

We present an analytical theory describing a novel phenomenon of enhanced backscattering corresponding to the spatial refocussing of a spread-out correlated wave packet due to a brief interaction with a disordered potential. Our theory is validated by numerical simulations and explains the physics observed in recent experiments on cold atom transport in disorder.

cond-mat.dis-nn↗
arXiv2012

Bunching and anti-bunching of localised particles in disordered media

We consider pairs of non-interacting quantum particles transmitted through a disordered medium, with emphasis on the role of their quantum statistics. It is shown that particle-number correlations measured in transmission are strikingly sensitive to the quantum nature of the particles when they undergo Anderson localisation, due to bosonic bunching and fermionic anti-bunching in the scattering channels of the medium. The case of distinguishable particles is also discussed.

cond-mat.dis-nn↗
arXiv2012

Coherent Backscattering of Ultracold Matter Waves: Momentum Space Signatures

Using analytical and numerical methods, it is shown that the momentum distribution of a matter wave packet launched in a random potential exhibits a pronounced coherent backscattering (CBS) peak. By analyzing the momentum distribution, key transport times can be directly measured. The CBS peak can be used to prove that transport occurs in the phase-coherent regime, and measuring its time dependence permits monitoring the transition from classical diffusion to Anderson localization.

cond-mat.dis-nn↗
arXiv2011

Fokker-Planck equation for transport of wave packets in nonlinear disordered media

Starting from first principles, we formulate a theory of wave packet propagation in a nonlinear, disordered medium of any dimension, through the derivation of a Fokker-Planck transport equation. Our theory is based on a diagrammatic expansion of the wave packet's density, and is supported by a heuristic picture that involves a Boltzmann equation with an effective, external potential. Our approach also confirms results obtained in previous work for two-dimensional, nonlinear disordered media.

cond-mat.dis-nn↗