Decoherence and the Reemergence of Coherence From a Superconducting "Horizon''

TL;DR

This paper explores how a superconducting analogue of a black hole horizon causes initial decoherence in a quantum interferometer, but coherence reemerges at stronger coupling due to resonant tunneling, mimicking gravitational phenomena.

Contribution

It demonstrates the reemergence of quantum coherence in a superconducting analogue of a black hole horizon, highlighting a novel interplay between decoherence and resonant tunneling.

Findings

Decoherence occurs at weak coupling due to Andreev reflection.

Coherence reemerges at stronger coupling via resonant tunneling through Andreev bound states.

Analogous gravitational phenomena are suggested by the reemergence of coherence.

Abstract

In a recent paper [arXiv:2205.06279], Danielson et al. demonstrated that the mere presence of a black hole causes universal decoherence of quantum superpositions (dubbed the DSW decoherence). We analyze decoherence in a superconducting analogue [arXiv:1709.06154] of the event horizon of a black hole, where Andreev reflection plays the role of Hawking radiation. We consider a normal metal interferometer threaded by an Aharonov-Bohm flux, where one of the arms of the interferometer is coupled to a superconductor by a tunnel coupling of varying strength. At absolute zero temperature and for weak coupling, we find that the scattering states of the interferometer are decohered by Andreev reflection, a nontrivial manifestation of the proximity effect analogous to DSW decoherence from the event horizon of a black hole. However, for increasing coupling strength to the superconductor, we find a reemergence of coherence via resonant tunneling through Andreev bound states. This suggests the existence of an analogue gravitational phenomenon wherein transmission mediated by virtual Hawking radiation leads to a reemergence of coherence in an interferometer placed within a few Compton wavelengths of a black hole's event horizon.