Reduction of Quantum Phase Fluctuations in a Laser Via Squeezed Vacuum Reservoir
The source of the natural linewidth of a laser associated with a phase diffusion is spontaneous emission. If the phases of the spontaneously emitted photons are influenced, the phase diffusion rate can be modified . Our scheme for laser is based on four-level atoms in a ‘squeezed vacuum’. We consider a modification of the scheme proposed by Gea-Banacloche  by including a separate ‘squeezed vacuum’ reservoir which couples the spontaneous decay of the atouts between the lasing levels. We assume that all time modes coupling to the atouts are squeezed so that the spontaneous emission related to the decay constant takes place only into these modes. We consider the effect of transmission losses similar to the one described by Gea-Banacloche. It is shown that the spontaneous decay between the lasing levels brings stability of the phase locking and the transmission losses contribute to time reduction of the phase diffusion.