Criteria for system-environment entanglement generation for systems of any size in pure-dephasing evolutions

TL;DR

This paper establishes criteria to distinguish entangling from non-entangling pure dephasing evolutions in systems larger than a qubit, revealing that operator commutation conditions determine entanglement generation.

Contribution

It generalizes the single-qubit separability criterion to larger systems and identifies additional conditions involving environmental operators for entanglement detection.

Findings

Product of environmental operators must commute for no entanglement

Commutation with initial environment state is not sufficient for separability

Entanglement can occur even with a completely mixed environment

Abstract

An evolution between a system and its environment which leads to pure dephasing of the system may either be a result of entanglement building up between the system and the environment or not (the second option is only possible for initially mixed environmental states). We find a way of distinguishing between an entangling and non-entangling evolutions for systems which are larger than a single qubit. The generalization of the single qubit separability criterion to larger systems is not sufficient to make this distinction (it constitutes a necessary condition of separability). A set of additional conditions for the operators describing the evolution of the environment depending on the state of the system is required. We find that the commutation of these environmental operators with the initial state of the environment does not guarantee separability, products of the operators need to commute among themselves for a pure dephasing evolution not to be accompanied by system-environment entanglement generation. This is a qualitative difference with respect to the single-qubit case, since it allows for a system to entangle with an initially completely mixed environment.