Quantum Recoherence in Presence of Excited States in the Early Universe

TL;DR

This paper studies how primordial quantum fluctuations in the early universe can regain quantum coherence, showing that only the Bunch-Davies vacuum fully recoheres while excited states retain residual quantum correlations, revealing sensitivity to initial conditions.

Contribution

It introduces a detailed analysis of recoherence phenomena in a two-field inflationary model, highlighting the unique role of the Bunch-Davies vacuum and the persistence of quantum correlations in excited states.

Findings

Only the Bunch-Davies vacuum undergoes full recoherence.

Excited states exhibit residual quantum correlations indefinitely.

Recoherence is highly sensitive to initial quantum states.

Abstract

We investigate the quantum-to-classical transition of primordial perturbations within a two-field inflationary framework where an adiabatic mode interacts with an entropic environment. In the case of a massive entropic environment, the attractor Bunch--Davies vacuum plays a special role: it is the only state that can undergo full recoherence, whereas all excited initial states exhibit persistent loss of purity. To characterize this behavior, we parameterize excited Gaussian initial states by their Bogoliubov coefficients and compute the purity and R\'enyi-2 entropy of the reduced adiabatic state as information-theoretic indicators of decoherence dynamics. We find that excited states display \emph{purity-freezing} at a non-zero plateau, where residual quantum correlations persist indefinitely, a qualitative departure from the complete recoherence observed for the Bunch--Davies vacuum. This sensitivity to initial conditions highlights the non-generic nature of full recoherence in the quantum-to-classical transition of inflationary perturbations.