Backreaction and Unruh effect: New insights from exact solutions of uniformly accelerated detectors

TL;DR

This paper provides exact solutions for an accelerated Unruh-DeWitt detector, revealing new dynamical features, the limits of the Unruh effect, and the impact of backreaction and entanglement on the detector's thermal perception.

Contribution

It introduces nonperturbative exact solutions showing how backreaction and entanglement affect the Unruh effect and detector dynamics beyond perturbation theory.

Findings

Unruh effect is operative only in ultra-weak coupling and high acceleration limits.

Entanglement causes the detector to be in a mixed state even in vacuum.

Late-time detector behavior deviates from a perfect thermal distribution.

Abstract

Using nonperturbative results obtained recently for an uniformly accelerated Unruh-DeWitt detector, we discover new features in the dynamical evolution of the detector's internal degree of freedom, and identified the Unruh effect derived originally from time-dependent perturbation theory as operative in the ultra-weak coupling and ultra-high acceleration limits. The mutual interaction between the detector and the field engenders entanglement between them, and tracing out the field leads to a mixed state of the detector even for a detector at rest in Minkowski vacuum. Our findings based on this exact solution shows clearly the differences from the ordinary result where the quantum field's backreaction is ignored in that the detector no longer behaves like a perfect thermometer. From a calculation of the evolution of the reduced density matrix of the detector, we find that the transition probability from the initial ground state over an infinitely long duration of interaction derived from time-dependent perturbation theory is existent in the exact solution only in transient under special limiting conditions corresponding to the Markovian regime. Furthermore, the detector at late times never sees an exact Boltzmann distribution over the energy eigenstates of the free detector, thus in the non-Markovian regime covering a wider range of parameters the Unruh temperature cannot be identified inside the detector.