In this paper two different behaviors of a V-type three-level atom which is driven by a classical field in an optical cavity are shown. We show that the behavior of an atom depends on the values of the critical photon number. The system treatment for large enough values of the critical photon number is described by the semiclassical laser theory. In contrast, for small enough values of the critical photon number, the system shows new quantum properties. In the former case, it is shown that the system performs like a conventional laser and in the latter one, the system acts as an effective two-level model. The behaviors of the system are investigated both in the semiclassical approximation and full quantum theory. For comparing the results, computer simulations are implemented.
IntroductionA one-atom laser, a device which utilizes a trapped atom for the amplification of the laser field, is a system of interest in quantum optics. In the last decade there have been many theoretical and experimental demonstrations for realizing such a device [1,2]. A single-atom laser, in which no more than one atom is present in an optical resonator, is one of the key systems to study quantum effects in the interaction of electromagnetic fields with matter [3]. In [2] and [4], Ã-type and V-type three-level atom are described, respectively. In this paper, a V-type three-level atom, similar to [4] is considered and the effect of critical photon number on such a device is investigated. The results show that significant changes in the lasing and non-lasing regimes and also in the weak driving limit are derived in comparison with [2]. By defining dimensionless parameters, we show that the main role of the system is characterized by the critical photon number, N G . For sufficiently large values of N G , the system acts as a conventional laser and its behavior is modeled by the semiclassical laser theory. For small enough values of N G and in the weak driving limit, new quantum properties arise in the system. In this regime the system can be approximated by an effective two-level atom. By computer simulation, we find that the full quantum theory justifies the predictions of the semiclassical approach and the effective two-level model.
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