Entanglement Reactivation in Separable Environments

TL;DR

This paper demonstrates that separable correlations in correlated-noise environments can reactivate and preserve entanglement during transmission, even under extreme decoherence, revealing new ways to distribute entanglement in realistic settings.

Contribution

It introduces the concept that separable correlations can restore entanglement in environments previously thought to be entanglement-breaking, especially in Gaussian settings.

Findings

Separable correlations can reactivate entanglement in correlated-noise environments.

Entanglement preservation is possible without decoherence-free subspaces.

Restoration occurs only after a critical correlation threshold is exceeded.

Abstract

Combining two entanglement-breaking channels into a correlated-noise environment restores the distribution of entanglement. Surprisingly, this reactivation can be induced by the injection of separable correlations from the composite environment. In any dimension (finite or infinite), we can construct classically-correlated "twirling" environments which are entanglement-breaking in the transmission of single systems but entanglement-preserving when two systems are transmitted. Here entanglement is simply preserved by the existence of decoherence-free subspaces. Remarkably, even when such subspaces do not exist, a fraction of the input entanglement can still be distributed. This is found in separable Gaussian environments, where distillable entanglement is able to survive the two-mode transmission, despite being broken in any single-mode transmission by the strong thermal noise. In the Gaussian setting, entanglement restoration is a threshold process, occurring only after a critical amount of correlations has been injected. Such findings suggest new perspectives for distributing entanglement in realistic environments with extreme decoherence, identifying separable correlations and classical memory effects as physical resources for "breaking entanglement-breaking".