Phase diagram for the one-way quantum deficit of two-qubit X states

TL;DR

This paper constructs a comprehensive phase diagram for the one-way quantum deficit in two-qubit X states, revealing significant regions with variable optimal measurement angles, which could facilitate experimental detection of quantum correlations.

Contribution

It provides the first complete phase diagram for the one-way quantum deficit in the XXZ subclass of symmetric X states, highlighting the large size of the variable angle region.

Findings

The variable measurement angle region is significantly larger than previously thought.

The phase diagram reveals distinct regions with constant and variable optimal measurement angles.

Potential for experimental detection of quantum correlations with variable measurement angles.

Abstract

The one-way quantum deficit, a measure of quantum correlation, can exhibit for X quantum states the regions (subdomains) with the phases $\Delta_0$ and $\Delta_{\pi/2}$ which are characterized by constant (i.e., universal) optimal measurement angles, correspondingly, zero and $\pi/2$ with respect to the $z$-axis and a third phase $\Delta_\vartheta$ with the variable (state-dependent) optimal measurement angle $\vartheta$. We build the complete phase diagram of one-way quantum deficit for the XXZ subclass of symmetric X states. In contrast to the quantum discord where the region for the phase with variable optimal measurement angle is very tiny (more exactly, it is a very thin layer), the similar region $\Delta_\vartheta$ is large and achieves the sizes comparable to those of regions $\Delta_0$ and $\Delta_{\pi/2}$. This instils hope to detect the mysterious fraction of quantum correlation with the variable optimal measurement angle experimentally.