JQI Seminar 10/2/2017 - Xiao Li and Tobias Huber

"Observation of mobility edges in a one-dimensional bichromatic incommensurate potential"

Speaker: Xiao Li, JQI

Abstract: In this talk I will focus on a one-dimensional (1D) mutually incommensurate bichromatic lattice system which has been implemented in ultracold atoms to study quantum localization. It has been universally believed that the tight-binding version of this bichromatic incommensurate system is represented by the well-known Aubry-Andre model. Here we establish that this belief is incorrect and that the Aubry-Andre model description, which applies only in the extreme tight-binding limit of very deep primary lattice potential, generically breaks down near the localization transition due to the unavoidable appearance of single-particle mobility edges (SPME). As a result, for the full lattice system, an intermediate phase between completely localized and completely delocalized regions appears due to the existence of the SPME, making the system qualitatively distinct from the Aubry-Andre prediction. Our theoretical prediction is subsequently verified in an experiment using a one-dimensional quasi-periodic optical lattice. In particular, a regime is identified where extended and localized single-particle states coexist, in good agreement with our theoretical results. Our work thus presents the first realization of a system with a SPME in one dimension, and it opens up more research prospects in the context of manybody localization, including the question of manybody mobility edges.

"Quantum dots as photon sources"

Speaker: Tobias Huber, JQI

Abstract: In this talk I will introduce semiconductor quantum dots and show how we use them to create single photons. I will show how two-photon resonant excitation can be used to address a forbidden transition and how we use this to create time-bin entangled photons. I will present how to perform tomography on time-bin entangled photons and conclude with some results.