Decoherence by warm horizons

TL;DR

This paper offers a local perspective on decoherence caused by soft photon and graviton radiation near horizons, demonstrating that finite temperature environments induce steady decoherence through quantum fluctuations.

Contribution

It maps the global decoherence process onto a local worldline model, clarifying the role of temperature and the Unruh effect in horizon-induced decoherence.

Findings

Decoherence arises from local random forces related to the Unruh effect.

Finite temperature environments cause steady decoherence via fluctuation-dissipation mechanisms.

The local model aligns with the global description by Danielson, Satishchandran, and Wald.

Abstract

Recently Danielson, Satishchandran, and Wald (DSW) have shown that quantum superpositions held outside of Killing horizons will decohere at a steady rate. This occurs because of the inevitable radiation of soft photons (gravitons), which imprint a electromagnetic (gravitational) ``which-path'' memory onto the horizon. Rather than appealing to this global description, an experimenter ought to also have a local description for the cause of decoherence. One might intuitively guess that this is just the bombardment of Hawking/Unruh radiation on the system, however simple calculations challenge this idea -- the same superposition held in a finite temperature inertial laboratory does not decohere at the DSW rate. In this work we provide a local description of the decoherence by mapping the DSW set-up onto a worldline-localized model resembling an Unruh-DeWitt particle detector. We present an interpretation in terms of random local forces which do not sufficiently self-average over long times. Using the Rindler horizon as a concrete example we clarify the crucial role of temperature, and show that the Unruh effect is the only quantum mechanical effect underlying these random forces. A general lesson is that for an environment which induces Ohmic friction on the central system (as one gets from the classical Abraham-Lorentz-Dirac force, in an accelerating frame) the fluctuation-dissipation theorem implies that when this environment is at finite temperature it will cause steady decoherence on the central system. Our results agree with DSW and provide the complementary local perspective.