title: Quantum thermalization through entanglement in an isolated many-body system.
abstract: Statistical mechanics relies on the maximization of entropy in a system at thermal equilibrium. However, an isolated quantum many-body system initialized in a pure state remains pure during Schrödinger evolution, and in this sense it has static, zero entropy. We experimentally studied the emergence of statistical mechanics in a quantum state and observed the fundamental role of quantum entanglement in facilitating this emergence. Microscopy of an evolving quantum system indicates that the full quantum state remains pure, whereas thermalization occurs on a local scale. We directly measured entanglement entropy, which assumes the role of the thermal entropy in thermalization. The entanglement creates local entropy that validates the use of statistical physics for local observables. Our measurements are consistent with the eigenstate thermalization hypothesis.
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Kaufman
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: M Eric
authors.initials: ME
authors.lastname: Tai
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lukin
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Rispoli
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Schittko
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Philipp M
authors.initials: PM
authors.lastname: Preiss
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA. greiner@physics.harvard.edu.
authors.forename: Markus
authors.initials: M
authors.lastname: Greiner