We present a reliable algorithm to evaluate quantum discord for general two-qubit states, amending and extending an approach recently put forward for the subclass of X states. A closed expression for the discord of arbitrary states of two qubits cannot be obtained, as the optimization problem for the conditional entropy requires the solution to a pair of transcendental equations in the state parameters. We apply our algorithm to run a numerical comparison between quantum discord and an alternative, computable measure of nonclassical correlations, namely, the geometric discord. We identify the extremally nonclassically correlated two-qubit states according to the (normalized) geometric discord, at a fixed value of the conventional quantum discord. The latter cannot exceed the square root of the former for systems of two qubits. © 2011 American Physical Society.
Quantum discord for general two-qubit states: Analytical progress / Girolami, D.; Adesso, G.. - In: PHYSICAL REVIEW A. - ISSN 1050-2947. - 83:5(2011), p. 052108.
Titolo: | Quantum discord for general two-qubit states: Analytical progress |
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Data di pubblicazione: | 2011 |
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Digital Object Identifier (DOI): | http://dx.doi.org/10.1103/PhysRevA.83.052108 |
Appare nelle tipologie: | 1.1 Articolo in rivista |
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http://hdl.handle.net/11583/2849519