Resonances and microscopic irreversibility: An introduction

Édgar Roldán

Edgar Revéiz

Amnon Aharony A

Tiago B. Batalhão, Alexandre M. Souza, Roberto S. Sarthour +4 more

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.

E. Susana Hernández, Hernán Gustavo Solari

It is shown that nuclear matter described by quasispin or pseudospin operators may exhibit irreversible behavior, in the sense of modern kinetic theory. With the help of the group-contraction technique, a harmonic oscillator can be associated to the many-body system and it is seen that in the standard Lipkin-Meshkov-Glick model the ground-state phase transition gives rise to a significant change in the spectral properties of the characteristic operators. This fact makes room for the introduction of the microscopic operators of irreversible dynamics. Their meaning and the consequences of their existence are examined and it is seen that the time evolution of the quasispin arrangement closely resembles the approach to equilibrium of a macroscopic system.NUCLEAR STRUCTURE Operators of irreversible Hamiltonian dynamics; quasispin nuclear matter; group contraction, Lipkin-Meshkov-Glick model; ground-state phase transition; entropy; irreversible approach to equilibrium.

Roberto Laura