Coherent multiple scattering of out-of-equilibrium interacting Bose gases

Non-equilibrium pre-thermal states in a two-dimensional photon fluid

“…It describes the initial relaxation toward a quasi-steady state after a perturbation. While having similar properties to their thermal counterparts, pre-thermal states exhibit a partial memory of initial conditions [1][2][3][4][5][6][7][8][9]. Here, we observe the dynamical formation of a pre-thermal state in a non-equilibrium, two-dimensional (2D) fluid of light after an interaction quench.…”

“…Here, we generalize this method to the configuration of our experiment, where the background is a spatially-dependent Gaussian field. We thus model the field impinging on the atomic cell at z = 0 as Ψ 0 (r) = I(r) 1 + ψ s (r) (9) where I(r) = I 0 /(1 + 2 ) exp(−2r 2 /w 2 0 ) is the Gaussian background [r = (x, y), w 0 beam waist] and ψ s (r) a speckle field. The latter can be accurately modeled as a complex, Gaussian random variable with Gaussian correlation function…”

“…To confirm the validity of eq. ( 30), and the subsequent predictions (31) and (32) used in the main text to interpret experimental measurements, we have performed direct numerical simulations of g (1) by propagating the initial state (9) with the Gross-Pitaevskii equation. This propagation relies on a standard split-step method, using a system of size L x = L y = 6 discretized on a 1024×1024 spatial grid.…”

Disorder in order: Localization without randomness in a cold atom system

“…The observation of the mobility edge using the expansion of atomic matter waves through disordered speckle potentials has sparked recent theoretical [71,72] and experimental interest [41,73,74]. Discrepancies between theory and experiments remain, however, as to the position of the mobility edge [72,75]. On the theory side, the problem is difficult because it requires going beyond the perturbative weak disorder regime and treating fully the speckle potential, while for experiments it is difficult to prepare a sufficiently narrow energy distribution of the atomic cloud.…”

Dynamical emergence of a Kosterlitz-Thouless transition in a disordered Bose gas following a quench

“…Initially described in one-dimensional geometries [20,21], manybody localization has also been recently touched upon in two dimensions [22][23][24][25]. In parallel, the ergodic regime has been explored in weakly interacting disordered Bose gases, where it was shown that at transient times the competition between disorder and interactions can destroy localization effects [26][27][28][29] or drive the gas to a pre-thermal state [30,31].…”