Quantum discord for general two--qubit states: Analytical progress

Abstract

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 non-classical correlations, namely the geometric discord. We identify the extremally non-classically correlated two--qubit states according to the (normalized) geometric discord, at fixed value of the conventional quantum discord. The latter cannot exceed the square root of the former for systems of two qubits.

8 pages, 2 figures

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Cited by in corpus (11)

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• Dynamics of entropic measurement-induced nonlocality in structured reservoirs
• Quantum resources for hybrid communication via qubit-oscillator states
• Geometric interpretation of the geometric discord
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• Various Correlations in Anisotropic Heisenberg XYZ Model with Dzyaloshinski-Moriya Interaction
• Quantum discord in quantum random access codes and its connection with dimension witness
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