Relaxation and Prethermalization in an Isolated Quantum System

Abstract

Prethermalization: When a physical system is subjected to a rapid change of conditions (for example, a gas of atoms is allowed to occupy a volume twice the size of the original container), it quickly achieves a new temperature (thermalizes) through collisions. However, in some quantum systems many conserved variables inhibit thermalization; understanding the phases the systems go through in the slowing process is of great interest to cosmologists and physicists. Gring et al. (p. 1318 , published online 31 August) separate an ultracold one-dimensional gas of bosonic atoms into two nearly identical halves, and follow how local differences in phase between the halves evolve in time by examining their interference. Initially, the local phases are almost identical, but a rapid decoherence ensues, followed by a very slow further decay. The authors analyze the relative state reached after the initial fast decay and find that it can be described by an equilibrium function with an effective temperature several times less than the initial temperature. Because this cannot be the final state of the system, the authors term the initial process prethermalization.