The two qubit (spin 1/2) singlet state has invariant perfect EPR correlations: if two observers measure {\em any} identical observables the results are always perfectly (anti-)correlated. We show that no such correlations exists in $d\otimes d$ pure or mixed bipartite quantum states if $d\geq3$ . This points that two qubit singlets are high-quality quantum information carriers in long distance transmission: their correlations are unaffected by identical random unitary transformations of both qubits. Pairs of entangled qu $d$ its, $d>2$ , do not have this property. Thus, qu $d$ it properties should be rather exploited only in protocols in which transmission is not a long distance one.The two qubit (spin 1/2) singlet state has invariant perfect EPR correlations: if two observers measure {\em any} identical observables the results are always perfectly (anti-)correlated. We show that no such correlations exists in $d\otimes d$ pure or mixed bipartite quantum states if $d\geq3$. This points that two qubit singlets are high-quality quantum information carriers in long distance transmission: their correlations are unaffected by identical random unitary transformations of both qubits. Pairs of entangled qu$d$its, $d>2$, do not have this property. Thus, qu$d$it properties should be rather exploited only in protocols in which transmission is not a long distance one.

arXiv:1109.1447Sep 7, 20110 citations

Correlations in a multi-qubit state

Dong Zhou, Bei Zeng, Zhu‐An Xu +1 more

Bulletin of the American Physical SocietyMar 13, 20060 citations

Local correlations of mixed two-qubit states

Fulin Zhang, Jing‐Ling Chen, Changliang Ren +1 more

arXiv:0909.1634Physics Letters AApr 11, 20101 citation

Dominance of quantum over classical correlations: entropic and geometric approach

Zbigniew Walczak, Iwona Wintrowicz, Zakrzewska, Katarzyna

Recently, it has been shown that there exist quantum states for which quantum correlations dominate over classical correlations. Inspired by this observation, we investigate the problem of quantum correlations dominance for two-qubit Bell diagonal states in the Ollivier--Zurek paradigm, using both entropic and geometric approach to quantification of classical and quantum correlations. In particular, we estimate numerically the amount of two-qubit Bell diagonal states for which quantum correlations dominate over classical correlations, and vice versa. Moreover, we show that in general these two approaches to quantification of correlations provide ambiguous results.Recently, it has been shown that there exist quantum states for which quantum correlations dominate over classical correlations. Inspired by this observation, we investigate the problem of quantum correlations dominance for two-qubit Bell diagonal states in the Ollivier--Zurek paradigm, using both entropic and geometric approach to quantification of classical and quantum correlations. In particular, we estimate numerically the amount of two-qubit Bell diagonal states for which quantum correlations dominate over classical correlations, and vice versa. Moreover, we show that in general these two approaches to quantification of correlations provide ambiguous results.

arXiv:1303.0366Mar 2, 20130 citations

Two qubits of a W state violate Bell’s inequality beyond Cirel’son’s bound

Adán Cabello

It is shown that the correlations between two qubits selected from a trio prepared in a W state violate the Clauser-Horne-Shimony-Holt inequality more than the correlations between two qubits in any quantum state. Such a violation beyond Cirel'son's bound is smaller than the one achieved by two qubits selected from a trio in a Greenberger-Horne-Zeilinger state [A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. However, it has the advantage that all local observers can know from their own measurements whether or not their qubits belong to the selected pair.It is shown that the correlations between two qubits selected from a trio prepared in a W state violate the Clauser-Horne-Shimony-Holt inequality more than the correlations between two qubits in any quantum state. Such a violation beyond Cirel'son's bound is smaller than the one achieved by two qubits selected from a trio in a Greenberger-Horne-Zeilinger state [A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. However, it has the advantage that all local observers can know from their own measurements whether or not their qubits belong to the selected pair.

arXiv:quant-ph/0205183Physical Review AOct 22, 200215 citations

Quantum correlations of two qubits interacting with a macroscopic medium

Yan Liu, Jing Lu, Lan Zhou

arXiv:1410.6317Quantum Information ProcessingJan 28, 20154 citations

d\otimes d

pure or mixed bipartite quantum states if

d\geq3

. This points that two qubit singlets are high-quality quantum information carriers in long distance transmission: their correlations are unaffected by identical random unitary transformations of both qubits. Pairs of entangled qu

d

its,

d>2

, do not have this property. Thus, qu

d

it properties should be rather exploited only in protocols in which transmission is not a long distance one.