Berlin 2005 – wissenschaftliches Programm
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Q: Quantenoptik und Photonik
Q 33: Quantenkommunikation II
Q 33.2: Vortrag
Dienstag, 8. März 2005, 11:00–11:15, HU Audimax
Discrimination of two mixed quantum states — •Ulrike Herzog1, János A. Bergou2, and Oliver Benson1 — 1Institut für Physik, Humboldt-Universität zu Berlin — 2Department of Physics, Hunter College, City University of New York
Distinguishing nonorthogonal quantum states is a basic prerequisite in quantum communication. Different measurement schemes have been developed to accomplish this task in an optimized way. Minimum-error discrimination yields an ambiguous result, with a minimum probability that it is erroneous. Optimum unambiguous, i. e., error-free, discrimination is a probabilistic measurement with a minimized probability of getting an inconclusive outcome, where the measurement fails to give a definite answer.
We consider the discrimination between two arbitrary but known mixed quantum states, occurring with given prior probabilities. In this case the lower bound of the failure probability in unambiguous discrimination is proportional to the fidelity of the two states [1]. Making use of an alternative derivation of the lower bound, we discuss the conditions under which it can be actually reached in a generalized measurement. For special given states we determine the detection operators describing the measurement that yields optimum unambiguous discrimination. We also show that the minimum failure probability in the error-free measurement scheme is always at least twice as large as the minimum error probability in ambiguous discrimination [2].
[1] T. Rudolph et al., Phys. Rev. A 68, 010301(R) (2003).
[2] U. Herzog and J. A. Bergou, Phys. Rev. A 70, 022302 (2004).