Superactivation of memory effects in a classical Markov environment

TL;DR

This paper explores the superactivation phenomenon where two non-Markovian dynamics combined exhibit information backflow, revealing new insights into classical Markov environments and quantum correlations.

Contribution

It demonstrates that superactivation of information backflow occurs in classical Markov environments and clarifies the role of quantum correlations without entanglement.

Findings

Superactivation occurs in classical Markov environments.

Backflow of information can be witnessed without entanglement.

The mechanism applies in both discrete and continuous-time dynamics.

Abstract

We investigate a phenomenon known as Superactivation of Backflow of Information (SBFI); namely, the fact that the tensor product of a non-Markovian dynamics with itself exhibits Backflow of Information (BFI) from environment to system even if the single dynamics does not. Such an effect is witnessed by the non-monotonic behaviour of the Helstrom norm and emerges in the open dynamics of two independent, but statistically coupled, parties. We physically interpret SBFI by means of the discrete-time non-Markovian dynamics of two open qubits collisionally coupled to an environment described by a classical Markov chain. In such a scenario SBFI can be ascribed to the decrease of the qubit-qubit-environment correlations in favour of those of the two qubits, only. We further prove that the same mechanism at the roots of SBFI also holds in a suitable continuous-time limit. We also show that SBFI does not require entanglement to be witnessed, but only the quantumness of the Helstrom ensemble.