Quantum and classical thermal correlations in theXYspin-12chain

Abstract

We investigate pairwise quantum correlation as measured by the quantum discord as well as its classical counterpart in the thermodynamic limit of anisotropic XY spin-1/2 chains in a transverse magnetic field for both zero and finite temperatures. Analytical expressions for both classical and quantum correlations are obtained for spin pairs at any distance. In the case of zero temperature, it is shown that the quantum discord for spin pairs farther than second-neighbors is able to characterize a quantum phase transition, even though pairwise entanglement is absent for such distances. For finite temperatures, we show that quantum correlations can be increased with temperature in the presence of a magnetic field. Moreover, in the XX limit, the thermal quantum discord is found to be dominant over classical correlation while the opposite scenario takes place for the transverse field Ising model limit.

Sudden change in quantum and classical correlations and the Unruh effect

“…Recent results showing that almost all (separable) quantum states actually have such nonclassical correlations [3] and that they can improve some computational tasks in comparison to when classical states are used [4,5] reinforce the relevance of such an issue. As a result, the last few years have witnessed an increasing number of articles discussing the quantification of these correlations [1,2,[6][7][8], their behavior under decoherence [9][10][11][12], and their relevance for quantum phase transitions [13][14][15][16].…”

General monogamy property of global quantum discord and the application

“…Quantum discord [16,17] is a widely accepted one among them. The quantum discord plays an important role in the research of quantum correlations due to its potential applications in a number of quantum processes, such as quantum critical phenomena [18][19][20][21], quantum evolution under decoherence [22,23] and, as we just mentioned, the DCQ1 protocol [24]. To quantify the multipartite quantum correlations, generalizations of bipartite quantum discord to multipartite states have been considered in various aspects [25][26][27][28].…”

Quantum discord and classical correlations in the bond-charge Hubbard model: Quantum phase transitions, off-diagonal long-range order, and violation of the monogamy property for discord

“…Quantum discord is a correlation measure aimed at quantifying all quantum correlations including entanglement. A key feature of QD is that in general it is not symmetric under exchange of the two subsystems 41 : measurement processes applied to the two different subsystems can lead to different values of discord. However, in the examples we will study the density matrices are symmetric with respect to the exchange of subsystem and so is the discord evaluated for the systems represented by these states.…”

“…The notion of QD has also been investigated, both from the theoretical 21,22 and the experimental side 23 , in the context of open quantum systems where it was shown that QD is generally more robust than entanglement to dissipation and thermal noise; moreover, QD is tightly related to complete positivity of quantum maps 24 . In the realm of many-body systems, the behavior of QD has been analyzed in relation to QPTs and thermal effects [25][26][27][28][29][30][31] . So far, the research has mostly concentrated on one-dimensional spin 1/2 models [25][26][27][28][29][30] .…”

“…In the realm of many-body systems, the behavior of QD has been analyzed in relation to QPTs and thermal effects [25][26][27][28][29][30][31] . So far, the research has mostly concentrated on one-dimensional spin 1/2 models [25][26][27][28][29][30] . The main results of these analyses show that two-point QD and CC between near as well as distant sites show clear signatures of QPTs (discontinuities or divergences), which can be understood within a general framework 25 and agree with finite-size scaling theory in the case of finite chains.…”