An entropic description of how an Unruh-DeWitt particle detector outside a Schwarzschild black hole thermalizes under Hawking radiation, treating the detector as an open quantum system and using quantum relative entropy (QRE) to capture path distinguishability and thermodynamic irreversibility. Shows that QRE resolves the thermalization beyond the Planckian transition rate, that it acquires position-dependent behavior set by the choice of black-hole vacuum (Boulware, Hartle-Hawking, Unruh), and that the detector's free-energy change can be recast so that a classical Kullback-Leibler term and a quantum-coherence term appear separately, with coherence consumed faster than its classical counterpart at high Hawking temperature.
A theoretical gravitational/quantum-information physics paper (gr-qc/hep-th/quant-ph) by Han, Ouyang, Hu and Feng that reformulates the thermalization of an Unruh-DeWitt (UDW) particle detector held …