Enhanced backscattering of a dilute Bose-Einstein condensate

Abstract

We study experimentally and numerically the quasi-bidimensional transport of a 87 Rb Bose-Einstein condensate launched with a velocity v0 inside a disordered optical potential created by a speckle pattern. A time-of-flight analysis reveals a pronounced enhanced density peak in the backscattering direction −v0, a feature reminiscent of coherent backscattering. Detailed numerical simulations indicate however that other effects also contribute to this enhancement, including a "backscattering echo" due to the position-momentum correlations of the initial wave packet.

Dynamics of localized waves in one-dimensional random potentials: Statistical theory of the coherent forward scattering peak

“…Indeed, observing the CBS effect [23] ensures that interference is at work and that phase coherence is preserved, while observing the CFS effect [24] makes sure that the bulk system has entered the AL regime. To date, while detection and characterization of the CBS peak in momentum space have been quickly reported for matter waves [25,26], the CFS peak still calls for an experimental observation. We propose to search for the CFS peak in a 1D speckle system as realized in [16] for example.…”

Inelastic Multiple Scattering of Interacting Bosons in Weak Random Potentials

“…It emerges due to counter-propagating wave amplitudes, whose constructive interference upon ensemble averaging leads • to an enhanced return probability to the origin within the medium, e. g. observed as unexpected magneto-resistance in quasi 2D metal films [49,50], and • to the prominent effect of coherent backscattering, i. e. an enhancement of the backscattered intensity, outside the medium. This enhancement, first observed for sunlight scattered back from the rings of Saturn [51], has since then been measured for acoustic waves [52], laser light scattered off polystyrene spheres [53] and cold atomic gases [54], and recently also for bosonic matter waves [55,56].…”

“…Furthermore, the presence of a nonlinearity may also produce an inversion of the backscattering cone [62], e. g. for matter waves in disordered potentials using the Gross-Pitaevskii equation [44]. As the experimental realization with matter waves [55,56] was just able to confirm the effect for non-interacting (or very weakly interacting) particles [63], an experimental confirmation of the -debatable (as we will see) -Gross-Pitaevskii result for stronger interaction [44] is still missing.…”

“…Although predicted theoretically e. g. by [44,62,63], an experimental observation -as a proof of principle -has only been conducted for the case of non-interacting atoms [55,56]. 4 In addition to the dephasing induced by elastic collisions as 4 The resolution of the experiments [55,56] only allows to identify the presence of a coherent backscattering cone. Dephasing effects that are experimentally present in addition to the very small residual atom-atom interaction have not been quantified yet.…”

“…The application to a stationary scattering setup with matter waves constitutes, on the one hand, a very timely scenario, as e. g. the developments of atom lasers and matter wave interferometers on atom chips, see Section 2.1, rapidly progress. On the other hand, many years of expertise have been gathered within the field of wave-packet spreading upon releasing the condensate from a trap into a new environment, where e. g. the first experiments on coherent backscattering of (non-interacting) matter waves have been reported recently [55,56]. Consequently, an extension of our theory to time-dependent scenarios based on recent progress in this field [186,187] presents a significant and feasible task.…”