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The emergence of decoherence in quantum electrodynamics is investigated. On combining superoperator methods with functional techniques from field theory, the degrees of freedom of a thermal radiation field are eliminated and the influence phase functional is derived which governs the reduced dynamics of the matter variables. Employing a prototypical interference device, a decoherence functional is developed which provides a gauge invariant relativistic measure for the degree of decoherence. It is demonstrated that the decoherence functional describes the destruction of quantum coherence through the emission of bremsstrahlung which is caused by the relative motion of the interfering components of a superposition. Explicit analytical expressions for the vacuum and the thermal contribution to the decoherence functional and for the corresponding coherence lengths are determined. These expressions reveal that bremsstrahlung leads to a fundamental decoherence mechanism which dominates for short times and which is present even in the electromagnetic field vacuum at zero temperature. The influence of bremsstrahlung on the center of mass coordinate of a system of many identical charged particles is also studied and is shown to lead to a strong suppression of quantum coherence.
Breuer et al. (Mon,) studied this question.