Quantum Correlations in Werner Derivatives

Peng Xu, Tao Wu, Liu Ye

Biao‐Liang Ye, Yimin Liu, Jianlan Chen +2 more

Sheng-Fang Wang, Yimin Liu, Guofeng Li +2 more

Quantum correlations in Werner derivatives are studied with two different approaches, i.e., measurement-induced disturbance (MID) [ Phys. Rev. A 77 (2008) 022301 ] and ameliorated MID (AMID) [ J. Phys. A 44 (2011) 352002 ]. They are derived via strict deductions with MID while numerically calculated via the measurement optimization with AMID. Interestingly, quantum correlations captured with both approaches are completely coincident. Moreover, some distinct features of the quantum correlations and their underlying physics are exposed via analyses and discussions.

C M Xie, Zhejing Zhang, H Yuan +3 more

Abstract Werner derivatives are a special kind of mixing states that originate from the Werner state due to unitary evolutions. In this paper, quantum correlation (QC) swapping between two Werner derivatives is studied. Quantum discord (Ollivier and Zurek 2001 Phys. Rev. Lett. 88 017901) is employed as the QC quantifier to characterize and quantify all QCs inhabited in the states which emerge during the swapping process. All concerned QCs are analytically or numerically worked out and their behaviors and properties such as monotony features and thresholds are concretely analyzed. Particularly, the QC properties of the four different final states corresponding to four different Bell states are revealed, compared and discussed. More importantly, it is found that, long-distance shared QCs can be generated from two short-distance ones via Bell-state measures in the middle nodes of a quantum network.

Eric Chitambar

In this article, we investigate how quantum correlations behave for the so-called Werner and pseudopure families of states. The latter refers to states formed by mixing any pure state with the totally mixed state. We derive closed expressions for the quantum discord and the relative entropy of quantumness for these families of states. For Werner states, the classical correlations are seen to vanish in high dimensions while the amount of quantum correlations remains bounded. For pseudopure states, nearly the opposite effect is observed, with both the quantum and classical correlations growing without bound as the dimension increases and only as the system becomes more entangled. In light of our calculations, we discuss how Werner states could play a role as a quantum one-time pad in cryptographic tasks and, along with isotropic states, could function as a quantum memory device designed to maximize the uncertainty tradeoff between noncommuting measurements on the individual subsystems.

O. Kübler, H. D. Zeh