Decoherence and disentanglement of qubits detecting scalar fields in an expanded universe

TL;DR

This paper investigates how the expansion of the universe affects quantum coherence and entanglement of qubits coupled to scalar fields, revealing that cosmic expansion enhances decoherence and can cause entanglement sudden death.

Contribution

It demonstrates, using an exactly solvable model, that universe expansion influences qubit decoherence and entanglement, providing a potential method to probe cosmic history through quantum detectors.

Findings

Expansion increases qubit decoherence.

Universe expansion degrades entanglement.

Possible entanglement sudden death depending on initial conditions.

Abstract

We consider Unruh-Wald qubit detector model adopted for the far future region of an exactly solvable 1+1 dimensional scalar field theory in a Robertson-Walker expanding spacetime. It is shown that the expansion of the universe in its history enhances the decoherence of the qubit coupled with a scalar field. Moreover, we consider two entangled qubits, each locally coupled a scalar field. The expansion of the universe in its history degrades the entanglement between the qubits, and can lead to entanglement sudden death if the initial entanglement is small enough. The details depend on the parameters characterizing the expansion of the universe. This work, albeit on a toy model, suggests that the history of the universe might be probed through the coherent and entanglement behavior of future detectors of quantum fields.