title: Irreversibility and the Arrow of Time in a Quenched Quantum System.
abstract: Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time. According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production. Using a nuclear magnetic resonance setup, we measure the nonequilibrium entropy produced in an isolated spin-1/2 system following fast quenches of an external magnetic field. We experimentally demonstrate that it is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a microscopic process and its time reversal. Our result addresses the concept of irreversibility from a microscopic quantum standpoint.
authors.affiliation: Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, 09210-580 Santo André, São Paulo, Brazil.|Faculty of Physics, University of Vienna, Boltzmangasse 5, Vienna A-1090, Austria.
authors.forename: T B
authors.initials: TB
authors.lastname: Batalhão
authors.affiliation: Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: A M
authors.initials: AM
authors.lastname: Souza
authors.affiliation: Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: R S
authors.initials: RS
authors.lastname: Sarthour
authors.affiliation: Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: I S
authors.initials: IS
authors.lastname: Oliveira
authors.affiliation: Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen's University, Belfast BT7 1NN, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Paternostro
authors.affiliation: Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Lutz
authors.affiliation: Department of Physics, University of York, York YO10 5DD, United Kingdom.
authors.forename: R M
authors.initials: RM
authors.lastname: Serra