Observable measure of bipartite quantum correlations

TL;DR

This paper introduces an experimentally accessible measure of bipartite quantum correlations that can be estimated with minimal measurements, applicable to various quantum systems including multiqubit states.

Contribution

The authors propose a new, state-independent measure of quantum correlations that can be experimentally determined without full state tomography, extending to higher-dimensional systems.

Findings

The measure Q can be computed from a small set of observable measurements.

Q is applicable to 2 x d systems, including multiqubit states.

The measurement effort does not increase with the dimension d.

Abstract

We introduce a measure Q of bipartite quantum correlations for arbitrary two-qubit states, expressed as a state-independent function of the density matrix elements. The amount of quantum correlations can be quantified experimentally by measuring the expectation value of a small set of observables on up to four copies of the state, without the need for a full tomography. We extend the measure to 2 x d systems, providing its explicit form in terms of observables and applying it to the relevant class of multiqubit states employed in the deterministic quantum computation with one quantum bit model. The number of required measurements to determine Q in our scheme does not increase with d. Our results provide an experimentally friendly framework to estimate quantitatively the degree of general quantum correlations in composite systems.