Physical Review A
Coherence properties of the N -atom-radiation interaction and the Holstein-Primakoff transformation
Franco Persico, G. Vetri
Abstract
We consider a system of $N$ two-level atoms initially in the ground state and interacting with a small [$〈n(t=0)〉\ensuremath{\ll}N$] coherent radiation field. The field is assumed to be monochromatic, and its wavelength is taken to be much larger than the dimensions of the region of the $N$ atoms. The statistical properties of both the atomic system and the radiation field are studied as functions of time. Using the Holstein-Primakoff transformation, it is shown that the initial coherence of the system tends to disappear after the energy of the system has been exchanged between atoms and field a number of times approximately given by $\frac{N}{〈n(t=0)〉}$.