[Paper Review] Coherent backscattering of a dilute Bose-Einstein condensate

G. Labeyrie, Tomasz Karpiuk+4 more|arXiv (Cornell University)|Jun 5, 2012

Cold Atom Physics and Bose-Einstein Condensates3 citations

TL;DR

This study investigates coherent backscattering in a quasi-bidimensional Bose-Einstein condensate (BEC) of $^{87}$Rb atoms injected into a disordered optical speckle potential. Using time-of-flight measurements and numerical simulations, it identifies a pronounced density peak at $-v_0$, confirming coherent matter wave transport, while also revealing a backscattering echo due to initial wave packet correlations, with radial integration unambiguously isolating the coherent peak as a signature of coherent scattering in a disordered medium.

ABSTRACT

We study experimentally and numerically the quasi-bidimensional transport of a $^{87}$Rb Bose-Einstein condensate launched with a velocity $v_0$ inside a disordered optical potential (speckle). A time-of-flight analysis reveals a pronounced enhanced density peak in the direction $-v_0$. Numerical simulations indicate that in addition to the coherent effect, a backscattering echo effect is also present due to the high position-momentum correlations of the initial wave packet. A radial integration of the atomic distributions allows us to unambiguously observe the coherent peak, a direct signature of coherent transport of atomic matter waves in a scattering medium.

Motivation & Objective

• To investigate coherent transport of matter waves in a disordered medium using a dilute Bose-Einstein condensate.
• To identify and disentangle coherent backscattering from additional echo effects arising from initial wave packet correlations.
• To experimentally observe and quantify the coherent backscattering peak using time-of-flight imaging and radial integration techniques.

Proposed method

• A $^{87}$Rb Bose-Einstein condensate is launched with a well-defined velocity $v_0$ into a quasi-bidimensional disordered optical potential generated by a laser speckle pattern.
• Time-of-flight expansion is used to map the momentum distribution of the atoms, revealing density peaks indicative of coherent scattering.
• Numerical simulations of the condensate dynamics are performed to model the transport and identify contributions from coherent backscattering and echo effects.
• Radial integration of the atomic density distribution is applied to isolate the coherent backscattering peak from background and echo contributions.

Experimental results

Research questions

• RQ1 Does coherent backscattering emerge in a dilute Bose-Einstein condensate propagating through a disordered optical potential?
• RQ2 To what extent do initial position-momentum correlations in the wave packet contribute to a backscattering echo effect?
• RQ3 Can the coherent backscattering peak be unambiguously identified in the presence of such echo effects using radial integration of the atomic distribution?

Key findings

• A pronounced density peak is observed in the time-of-flight images at momentum $-v_0$, directly indicating coherent backscattering of the matter wave.
• Numerical simulations reveal that the initial wave packet's high position-momentum correlations generate a distinct backscattering echo effect, superimposed on the coherent peak.
• Radial integration of the atomic distribution successfully isolates the coherent backscattering peak, confirming its presence as a robust signature of coherent transport.
• The combination of experimental data and simulations demonstrates that both coherent backscattering and echo effects coexist in the system, with the former being the dominant feature in the momentum distribution.