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

  • M. A. YurischevEmail author


The one-way quantum deficit, a measure of quantum correlation, can exhibit for X quantum states the regions (subdomains) with the phases \(\varDelta _0\) and \(\varDelta _{\pi /2}\) 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 \(\varDelta _\vartheta \) 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 \(\varDelta _\vartheta \) is large and achieves the sizes comparable to those of regions \(\varDelta _0\) and \(\varDelta _{\pi /2}\). This instils hope to detect the mysterious fraction of quantum correlation with the variable optimal measurement angle experimentally.


X density matrix One-way deficit function Domain of definition Piecewise-defined function Subdomains Critical lines and surfaces 



I am grateful to Dr. A. I. Zenchuk for his valuable remarks.


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Authors and Affiliations

  1. 1.Institute of Problems of Chemical PhysicsRussian Academy of SciencesChernogolovkaRussia

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