On the stability of the coherent state of a two-level atom Bose gas in the resonant laser field at zero temperature

TL;DR

This paper investigates the stability of a two-level atom Bose gas in a resonant laser field at zero temperature, revealing a mixture of two condensates, the existence of a gap mode, and conditions leading to instability due to nonideality.

Contribution

It introduces a stability analysis of the coherent state of a two-level atom Bose gas under intense laser fields, including the discovery of a gap mode and criteria for stability.

Findings

The Bose gas forms a mixture of two condensates with a fixed density ratio.

A gap mode exists with a magnitude proportional to the laser field amplitude.

Nonideality can cause instability and decay of the condensates.

Abstract

It is shown that a Bose gas of two-level atoms in the intense resonant laser field at zero temperature is a mixture of two condensates with a definite ratio of the densities. The criteria of stability are found for the stationary states of such system against the increment of the amplitudes of quasi Bogoliubov elementary excitations. Besides the usual acoustic mode the gap mode is shown to exist and the magnitude of the gap is proportional to the laser field amplitude. The involvement of the gas nonideality under definite conditions results in an instability and decay of the condensates.