Interaction-driven dynamical delocalization in a kicked one-dimensional ultracold gas

Abstract

This dissertation reports on the experimental observation of interaction-driven dynamical delocalization in a kicked one-dimensional ultracold gas. In the absence of interactions, particles in a one-dimensional disordered medium are localized due to quantum interference as predicted by the Anderson model. The evolution of this well-known localization phenomenon in the presence of interactions has been the subject of intense scrutiny in the past decades, including conflicting theoretical predictions in some cases. Using the quantum kicked rotor (QKR), we engineered the Anderson model in the synthetic momentum space where the equivalent localization phenomenon is termed dynamical localization. However, interaction effects had not been observed in earlier experimental observations of dynamical localization. We detail the implementation of a three-dimensional optical lattice that is used to control the interactions in the system and to realize the QKR Hamiltonian. Using ultracold gases in 1D tubes, we perform a quantum simulation of the QKR Hamiltonian in the presence of interactions and find that interactions destroy the localization and lead to slower-than-linear energy growth or sub-diffusive dynamics. The measured sub-diffusive exponents are not universal or monotonically varying with the various experimental parameters. However, we find that the onset time of delocalization is always shorter with stronger interaction or kick strengths. By temporally modulating the kick strength with incommensurate frequencies, we also engineered higher dimensional Anderson models and observed similar interaction-driven delocalization phenomena. The metal-insulator Anderson transition in the presence of interactions is also studied in the 3D case with varying kick strength. Our results shed light on interaction-driven transport, in a regime where theoretical approaches are extremely challenging and predict drastically different dynamics.