Quantum Kinetic Theory III: Quantum kinetic master equation for strongly condensed trapped systems

TL;DR

This paper develops a quantum kinetic theory for strongly Bose-condensed trapped atomic vapors, describing condensate growth, fluctuations, and equilibrium states with off-diagonal long-range order.

Contribution

It introduces a particle number conserving approach to quantum kinetics in strongly condensed trapped systems, extending previous theories.

Findings

Derived equations for particle number and phase fluctuations.

Described the growth dynamics of Bose-Einstein condensates.

Characterized the equilibrium state with off-diagonal long-range order.

Abstract

We extend quantum kinetic theory to deal with a strongly Bose-condensed atomic vapor in a trap. The method assumes that the majority of the vapor is not condensed, and acts as a bath of heat and atoms for the condensate. The condensate is described by the particle number conserving Bogoliubov method developed by one of the authors. We derive equations which describe the fluctuations of particle number and phase, and the growth of the Bose-Einstein condensate. The equilibrium state of the condensate is a mixture of states with different numbers of particles and quasiparticles. It is not a quantum superposition of states with different numbers of particles---nevertheless, the stationary state exhibits the property of off-diagonal long range order, to the extent that this concept makes sense in a tightly trapped condensate.