Berlin 2005 – scientific programme

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Q: Quantenoptik und Photonik

Q 34: Quanteninformation I

Q 34.3: Talk

Tuesday, March 8, 2005, 12:30–12:45, HU Audimax

Optimal unambiguous state discrimination of two density matrices and its link with the fidelity — •Philippe Raynal and Norbert Lütkenhaus — Institut für theoretische Physik I, Max-Planck-Forschungsgruppe, Universität Erlangen-Nürnberg, Staudtstr. 7/B1, 91058 Erlangen, Germany

Quantum state discrimination is a fundamental task in quantum information theory. One strategy is Unambiguous State Discrimination (USD). In that strategy the discrimination succeeds only with some probability. Whenever it succeeds, however, the discrimination is without error. The problem to find optimal USD strategies, which optimize the success probability, has been solved for many pure state scenarios, including any two pure states. However, no optimal USD has been described in the case of mixed states, unless that probem can be reduced to some pure state cases [1]. Bounds exist for the optimal success probability and they are given in terms of the fidelity [2,3]. In this contribution we study the case of two density matrices and present a wide class of mixed states for which exact solutions can be given. For this class, the bound is saturated.

[1] Ph. Raynal, N. Lütkenhaus, S. J. van Enk, Phys. Rev. A 68, 022308 (2003)

[2] T. Rudolph et al, Phys. Rev. A 68, 010301 (2003)

[3] Y. Feng et al, Phys. Rev. A 70, 012308 (2004)