General quantum mechanical theory of pure dephasing

Abstract

We consider the pure dephasing of a two-level system interacting linearly and quadratically with a bath of harmonic oscillators; the system studied is the most general harmonic two-surface problem. The temperature-dependent pure dephasing rate is calculated exactly to all orders in the system-bath interaction. Often this interaction can be expressed in terms of a small number of collective coordinates (linear combinations of bath modes). For the case of two such coordinates, we provide explicit expressions for the dephasing rate. If there is only a single collective coordinate, we recover our result from previous publications.