Observation of two-dimensional Anderson localisation of ultracold atoms

Donald H White,Donald H White,Maarten D Hoogerland,John L Helm,Mojdeh S Najafabadi,Daniel Schumayer,Daniel Schumayer,John L Helm,David A W Hutchinson,David A W Hutchinson,Christopher Gies,Dylan J Brown,Dylan J Brown,Dylan J Brown,Mojdeh S Najafabadi,John L Helm,Mojdeh S Najafabadi,Thomas A Haase,Thomas A Haase

doi:10.1038/s41467-020-18652-w

Abstract

Anderson localisation —the inhibition of wave propagation in disordered media— is a surprising interference phenomenon which is particularly intriguing in two-dimensional (2D) systems. While an ideal, non-interacting 2D system of infinite size is always localised, the localisation length-scale may be too large to be unambiguously observed in an experiment. In this sense, 2D is a marginal dimension between one-dimension, where all states are strongly localised, and three-dimensions, where a well-defined phase transition between localisation and delocalisation exists as the energy is increased. Here, we report the results of an experiment measuring the 2D transport of ultracold atoms between two reservoirs, which are connected by a channel containing pointlike disorder. The design overcomes many of the technical challenges that have hampered observation of localisation in previous works. We experimentally observe exponential localisation in a 2D ultracold atom system.

Highlights

Anderson localisation —the inhibition of wave propagation in disordered media— is a surprising interference phenomenon which is intriguing in two-dimensional (2D) systems
In this work we implement point scatterers in a 2D plane by projecting a blue-detuned 532 nm optical pattern shaped by a spatial light modulator (SLM) onto a flat, large-area twodimensional trap formed from 1064 nm light[36]
Η is the fraction of bright pixels within the channel displayed by the SLM

Summary

Introduction

Anderson localisation —the inhibition of wave propagation in disordered media— is a surprising interference phenomenon which is intriguing in two-dimensional (2D) systems. Observing Anderson localisation in 2D on reasonable length-scales, requires relatively strong scattering, and this leads to difficulty in distinguishing localisation effects from classical trapping; low energy particles have the shortest localisation lengths, yet they are trapped classically by the optical speckle To this end, Morong and DeMarco[35] suggested the use of randomly positioned point scatterers, which allows for a tuneable percolation threshold based on the amount of disorder, and allows for quantum interference effects to be effectively isolated from trapping effects. In a transport experiment the Bose gas is not in thermal equilibrium, which suppresses the formation of a Lifshits glass[40,41] (the mixture of low-energy single-particle localised states could mistakenly be identified as Anderson localisation) With these advantages, we tune between the weak- and strong-localised regimes[42], and observe compelling evidence for Anderson localisation of ultracold atoms in 2D

Methods

Results

Conclusion