### Abstract

Language | English |
---|---|

Article number | 365301 |

Number of pages | 18 |

Journal | Journal of Physics A: Mathematical and Theoretical |

Volume | 47 |

Issue number | 36 |

DOIs | |

Publication status | Published - 12 Sep 2014 |

### Fingerprint

### Keywords

- quantum correlations
- quantum operations
- quantum technologies
- quantum information

### Cite this

*Journal of Physics A: Mathematical and Theoretical*,

*47*(36), [365301]. https://doi.org/10.1088/1751-8113/47/36/365301

}

*Journal of Physics A: Mathematical and Theoretical*, vol. 47, no. 36, 365301. https://doi.org/10.1088/1751-8113/47/36/365301

**Discord of response.** / Roga, W.; Giampaolo, S. M.; Illuminati, F.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Discord of response

AU - Roga, W.

AU - Giampaolo, S. M.

AU - Illuminati, F.

PY - 2014/9/12

Y1 - 2014/9/12

N2 - The presence of quantum correlations in a quantum state is related to the stateʼs response to local unitary perturbations. Such a response is quantified by the distance between the unperturbed and perturbed states, minimized with respect to suitably identified sets of local unitary operations. In order to be a bona fide measure of quantum correlations, the distance function must be chosen among those that are contractive under completely positive and trace preserving (CPTP) maps. The most relevant instances of such physically well-behaved metrics include the trace, the Bures, and the Hellinger distance. To each of these metrics one can associate the corresponding discord of response, namely the trace, or Hellinger, or Bures minimum distance from the set of unitarily perturbed states. All these three discords of response satisfy the basic axioms for a proper measure of quantum correlations. In the present work we focus in particular on the Bures distance, which enjoys the unique property of being both Riemannian and contractive under CPTP maps, and admits important operational interpretations in terms of state distinguishability. We compute analytically the Bures discord of response for two-qubit states with maximally mixed marginals and we compare it with the corresponding Bures geometric discord, namely the geometric measure of quantum correlations defined as the Bures distance from the set of classical-quantum states. Finally, we investigate and identify the maximally quantum correlated two-qubit states according to the Bures discord of response. These states exhibit a remarkable nonlinear dependence on the global state purity.

AB - The presence of quantum correlations in a quantum state is related to the stateʼs response to local unitary perturbations. Such a response is quantified by the distance between the unperturbed and perturbed states, minimized with respect to suitably identified sets of local unitary operations. In order to be a bona fide measure of quantum correlations, the distance function must be chosen among those that are contractive under completely positive and trace preserving (CPTP) maps. The most relevant instances of such physically well-behaved metrics include the trace, the Bures, and the Hellinger distance. To each of these metrics one can associate the corresponding discord of response, namely the trace, or Hellinger, or Bures minimum distance from the set of unitarily perturbed states. All these three discords of response satisfy the basic axioms for a proper measure of quantum correlations. In the present work we focus in particular on the Bures distance, which enjoys the unique property of being both Riemannian and contractive under CPTP maps, and admits important operational interpretations in terms of state distinguishability. We compute analytically the Bures discord of response for two-qubit states with maximally mixed marginals and we compare it with the corresponding Bures geometric discord, namely the geometric measure of quantum correlations defined as the Bures distance from the set of classical-quantum states. Finally, we investigate and identify the maximally quantum correlated two-qubit states according to the Bures discord of response. These states exhibit a remarkable nonlinear dependence on the global state purity.

KW - quantum correlations

KW - quantum operations

KW - quantum technologies

KW - quantum information

U2 - 10.1088/1751-8113/47/36/365301

DO - 10.1088/1751-8113/47/36/365301

M3 - Article

VL - 47

JO - Journal of Physics A: Mathematical and Theoretical

T2 - Journal of Physics A: Mathematical and Theoretical

JF - Journal of Physics A: Mathematical and Theoretical

SN - 0305-4470

IS - 36

M1 - 365301

ER -