Decay of an atom coupled strongly to a reservoir

Abstract

An approach to the decay of a two-state quantum system coupled to a resonant environment is developed in terms of exact (nonperturbative) master equations. Starting from a quantum optical model of a two-level system coupled to a heatbath, it is shown that the effect of the bath can be replaced by one or more pseudomodes. This description is valid for a wide class of analytic density-of-state functions and it leads to exact master equations which fully describe the non-Markovian decay of the quantum system without the use of perturbation theory, the Born approximation, or the Markov approximation. Two examples are given: a simple model of a density-of-states gap which has two poles, and a non-Lorentzian resonance.