Characterizing quantumness via entanglement creation

TL;DR

This paper explores how an activation protocol can convert non-classical correlations into entanglement between original systems and ancillae, and characterizes the maximal non-classicality of certain two-qubit states.

Contribution

It demonstrates the use of an activation protocol for entangling original systems via entanglement swapping and bounds the quantumness measure for classical-quantum states.

Findings

Activation protocol enables entanglement creation between original systems.

Bound established for the relative entropy of quantumness in classical-quantum states.

Complete characterization of maximally non-classical two-qubit classical-quantum states.

Abstract

In [M. Piani et al., arXiv:1103.4032 (2011)] an activation protocol was introduced which maps the general non-classical (multipartite) correlations between given systems into bipartite entanglement between the systems and local ancillae by means of a potentially highly entangling interaction. Here, we study how this activation protocol can be used to entangle the starting systems themselves via entanglement swapping through a measurement on the ancillae. Furthermore, we bound the relative entropy of quantumness (a naturally arising measure of non-classicality in the scheme of Piani et al. above) for a special class of separable states, the so-called classical-quantum states. In particular, we fully characterize the classical-quantum two-qubit states that are maximally non-classical.