Probing many-body localization dynamics using ultracold fermions in an optical lattice

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The question of how an isolated quantum mechanical system thermalizes is not only significant in condensed matter physics, but it also invokes the intriguing problem of the apparent loss of information in a complex system as it thermalizes. A curious case is when a complex system fails to thermalize altogether -- a phenomenon known as many-body localization (MBL). Here, we propose to use interacting ultracold fermions in a lattice to experimentally study the distinctive properties of MBL using a novel set of observables. Among the questions in MBL debated intensely today are those concerning the existence of a many-body mobility edge, many-body intermediate phase and localization in higher dimensional lattice systems. Moreover, the striking relation between non-ergodicity and Hilbert space fragmentation is also not fully understood. In this view, our research objectives include: [1.] Stark many-body localization and Hilbert space fragmentation. We plan to study MBL in a tilted lattice, i.e., a Stark Hamiltonian and study non-ergodicity resulting from Hilbert space fragmentation. [2.] Bipartite fluctuations in an MBL system of >100 lattice sites: We propose to characterize the localization properties using bipartite fluctuations which is a proxy for the Entanglement entropy of a 1D lattice. [3.] Approximate theories for fermionic MBL systems: Due to the exponential Hilbert space dimension of an interacting many-body system, studying their properties numerically is also exponentially hard. We plan to use a quantum simulator with >100 lattice sites develop efficient approximate theories to describe these systems. The aforementioned projects are easily accessible to the current experimental capability and they will enhance our general understanding of MBL physics. Moreover, they also include a step towards developing ultracold atoms in a lattice into a quantum simulator, capable of solving hard problems.