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Journal of Physics A Mathematical and General

Solution of master equations for small bistable systems

Sarben Sarkar, J.S. Satchell

Published Jun 1, 1987• 18 citations
Publisher

Abstract

The master equations for bistability in the bad cavity limit in an atomic system is solved when the number of atoms N is not more than 45. A detailed comparison is made of results from Fokker-Planck equations and from the master equation. The validity of the decorrelation approximation for the master equation is examined.
DOI
10.1088/0305-4470/20/8/028

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Spontaneous emission from a system of NNN identical two-level atoms is considered using a master equation recently derived by the author. The master equation describing the time evolution of the phase-space distribution function associated with the reduced density operator of the atomic system is obtained. This master equation, which is of the type of a Fokker-Planck equation, is used to derive the equation of motion for the mean values of various atomic operators characterizing the physical properties of the system. This leads to a hierarchy of equations, which is decoupled by making a suitable approximation. The intensity of the spontaneously emitted radiation is then calculated. Next, the spontaneous emission from geometrically small systems is considered. For this case, the master equation is solved exactly, and an exact expression for the radiation rate is obtained. The exact solution of the master equation is also used to calculate the normally ordered correlation functions for the electric field. Section V deals with the spontaneous emission from a system of harmonic oscillators, the size of the system being small compared to a wavelength. The master equation for this problem is also solved exactly, and it is shown that this system also leads to superradiant emission in some cases, e.g., if all the oscillstors are excited initially to some coherent state ∣z0〉|{z}_{0}〉∣z0​〉.
In Chapter 9, we derived the master equation for a reduced density operator of a two-level atom coupled to a multi-mode vacuum field. We have seen that the master equation is an operator type equation that, in general, is not easy to solve. We have illustrated the solution of the master equation by representing the density operator in the basis of the two states of the two-level atom. The purpose of the representation of the master equation was to obtain c-number differential equations that are equivalent to the operator equations, but are more readily soluble.