Observation of the Topological Anderson Insulator in Disordered Atomic Wires

Disorder and topology have many deep connections, and can have a rich combined influence on the transport properties of quantum particles. Some of the most useful and intriguing properties of topological systems relate to the robustness of their edge states with respect to weak disorder. Rich phenomena are expected to occur as strong disorder is added to such systems, relating to the global unwinding of the non-local topological order. Surprisingly, it has even been predicted that the addition of disorder can induce topological order in otherwise topologically trivial materials. Despite these deep and rich connections, the difficulty of creating controlled disorder in real materials has prevented the exploration of disorder-driven changes in topology in experiments. Here we describe how a type of synthetic lattice can be engineered for dilute atomic gases at ultracold temperatures, allowing us to mimic the physics of disordered topological materials. We describe two types of topological transitions driven by the addition of disorder to one-dimensional atomic wires. The first is the breakdown of a nontrivial band topology by the addition of strong disorder, relating to a random-singlet topological transition. The second is a counter-intuitive ``order by disorder'' transition in which nontrivial topology arises due to disorder, relating to the observation of the topological Anderson insulator phase predicted nearly a decade ago. We discuss extensions to this result, including prospects for exploring disordered topological materials in higher dimensions.

In collaboration with Eric J. Meier - University of Illinois at Urbana; Fangzhao Alex An - University of Illinois at Urbana; Alexandre Dauphin - Barcelona Institute of Science and Technology, Complesso Universitario di Monte Sant’Angelo; Pietro Massignan - Barcelona Institute of Science and Technology, Universitat Politècnica de Catalunya; Taylor L. Hughes - University of Illinois at Urbana.