Quantum recoherence in the early universe

TL;DR

This paper uncovers a quantum recoherence mechanism in the early universe where adiabatic perturbations regain quantum coherence after initial decoherence, challenging previous assumptions about the irreversibility of quantum effects in cosmology.

Contribution

It introduces a novel recoherence mechanism for cosmological perturbations coupled to an entropic sector, supported by a non-Markovian master equation analysis.

Findings

Recoherence occurs after a transient decoherence phase.

Adiabatic perturbations exhibit significant late-time self-coherence.

Linear interactions in cosmology have no flat-space analogue.

Abstract

Despite being created through a fundamentally quantum-mechanical process, cosmological structures have not yet revealed any sign of genuine quantum correlations. Among the obstructions to the direct detection of quantum signatures in cosmology, environmental-induced decoherence is arguably one of the most inevitable. Yet, we discover a mechanism of quantum recoherence for the adiabatic perturbations when they couple to an entropic sector. After a transient phase of decoherence, a turning point is reached, recoherence proceeds and adiabatic perturbations exhibit a large amount of self-coherence at late-time. This result is also understood by means of a non-Markovian master equation, which reduces to Wilsonian effective-field theory in the unitary limit. This allows us to critically assess the validity of open-quantum-system methods in cosmology and to highlight that re(de)coherence from linear interactions has no flat-space analogue.