Southwest Quantum Information and Technology

Measuring entanglement entropy and local observables in a thermalizing many-body state

Presenting Author: Adam Kaufman, Greiner group (Harvard)
Contributing Author(s): Eric Tai, Alex Lukin, Matthew Rispoli, Philipp Preiss, Markus Greiner

Massive entanglement between the constituents of a many-body system is the defining feature of strongly correlated quantum systems. Recent theoretical developments point to the entropy of entanglement as a universal means to classify unusual quantum phases, such as spin liquids and topological phases. Despite its importance, there is no general scheme to experimentally verify entanglement in systems of interacting, delocalized particles. In this talk I will present an experimental scheme to probe entanglement in such itinerant systems through interference of two copies of a many-body state. Akin to Hong-Ou-Mandel interference of photons, this measurement performed with ultracold atoms in a quantum gas microscope probes the indistinguishability of quantum states. We directly measure quantum purity, second order Rényi entropy and mutual information for finite-sized Bose-Hubbard systems across the superfluid-insulator transition. More generally, our newly developed techniques can be used for detailed studies of disordered quantum systems or far-from-equilibrium dynamics. In recent experiments, we explore the evolution of quenched, isolated bosonic systems, where thermal ensembles appear to emerge from pure quantum states. We observe an approximate volume law scaling in the entanglement entropy and highlight its connection to the classical thermodynamic entropy, and we compare local measurements of the many-body state to the predictions of the eigenstate thermalization hypothesis.

Read this article online: http://www.nature.com/nature/journal/v528/n7580/full/nature15750.html

(Session 6 : Friday from 9:15 am - 9:45 am)