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Coherence and decoherence in the Harper-Hofstadter model

December 7, 2020 - 11:00am
Qi-Yu Liang
JQI postdoc seminar
Understanding how and when closed quantum systems lose or retain coherence is a central intellectual and practical question in quantum science. In rare cases, such as collisional narrowing or environment assisted tunneling, random processes can enhance coherence processes. In this talk, I will present a new addition to this list—the quasi-periodic lattice described by the Harper-Hofstadter (HH) model in a highly-elongated tube geometry, by showing that the dynamics can be immune to environmental noise. The interference of paths encircling the tube evokes an Aharonov-Bohm interferometer, which would be sensitive to a longitudinal flux threading the long axis of the tube. Surprisingly, by experimentally realizing the HH model using an atomic Bose-Einstein condensate, we find that our HH-interferometer depends on longitudinal flux only when the transverse flux is a rational fraction of the flux-quantum. Furthermore, at these rational values of transverse flux, the time evolution averaged over all possible values of the longitudinal flux returns to that at nearby irrational fluxes. Thus, the appealing intuitive picture of an Aharonov-Bohm interferometer is insufficient. Instead, I will explain our observations by transforming the HH model into a collection of momentum-space Aubry-André models.

We are hosting the Fall 2020 JQI Seminars virtually as Zoom meetings. JQI members and affiliates will receive a Zoom link in an email announcing each seminar. For those without access to Zoom, we will also be live streaming each seminar on YouTube. Once a seminar starts, you will find a link to the live stream on our YouTube page at