| Περίληψη: | We treat an Unruh-DeWitt detector as an open quantum system, with a quantum field playing the role of the environment, and evaluate the response of a uniformly accelerated detector for different types of interaction between the detector and the field. We derive the evolution equations for the reduced density matrix of the detector, invoking neither the Markov approximation nor the Rotating Wave Approximation (RWA). We find that at early times and in the regime of small accelerations, the non-Markovian effects are particularly pronounced, rendering the early-time transition rate non-thermal. The early-time transition rate strongly depends on the type of the interaction between the detector and the field and may not be in a Planckian form even in the Markovian regime of high accelerations. In contrast, the asymptotic state of an accelerated detector is always thermal at the Unruh temperature, regardless the internal characteristics of the interaction or the interacting field. The reduced density matrix of the detector at late times is thermal even if we take into account non-Markovian effects. We argue that the asymptotic state of an accelerated detector provides a more fundamental and persistent characterization of the acceleration temperature: A uniformly accelerated detector experiences the field vacuum as a genuine thermal bath at the Unruh temperature and eventually settles at a thermal state, regardless their intermediate dynamics or the type of interaction. This is a new interpretation of the Unruh effect that combines the formal aspects of quantum field theory and the operational approach of the Unruh-DeWitt detectors.
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