Decoherence of the field state in the single-mode laser

The rate at which an initially pure field state goes into mixture is calculated for the single-mode laser under the detailed balance condition. It is shown that the field state similar to the coherent state originally suggested by M. O. Scully and W. E. Lamb, Jr. is selected as the most stable state among squeezed states, and that the speed of whole decoherence process is strongly dependent on the quality factor Q of a laser cavity. In a laser cavity with extremely high quality factor, squeezed states other than the Scully-Lamb ansatz remain stable on the observation time scale.