Hannover 2003 – scientific programme

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Q: Quantenoptik

Q 50: Quantenkommunikation

Q 50.7: Talk

Friday, March 28, 2003, 15:30–15:45, F102

Criteria for quantum state discrimination with linear optics — •Peter van Loock and Norbert Lütkenhaus — Quantum Information Theory Group, Zentrum für Moderne Optik, Universität Erlangen-Nürnberg, Staudtstr. 7/B2, 91058 Erlangen

Measuring and hence distinguishing quantum states is an essential tool in quantum information processing. We derive sufficient and necessary conditions for the perfect distinguishability of arbitrary quantum states via linear optics including auxiliary photons. When conditional dynamics (a sequence of unitary transformations of the remaining modes conditioned upon the photon numbers detected in the first modes) is allowed, the conditions are still necessary for complete distinguishability. For a broad class of states commonly used in quantum information processing, it can be shown that auxiliary photons can never provide perfect distinguishability, if the states cannot be distinguished perfectly without auxiliary photons. For orthogonal sets of two-qubit and two-qutrit states, the conditions enable us to reproduce the known No-Go theorems [1,2,3] in a simple way. Furthermore, the simpler approach yields new No-Go results for more general classes of states, e.g., an orthogonal set of four states of two arbitrarily bad entangled qubits. For any given set of arbitrary quantum states, it always provides an efficient tool to decide on their distinguishability via linear optics.

[1] N. Lütkenhaus, J. Calsamiglia, and K.A. Suominen, Phys. Rev. A 59, 3295 (1999).

[2] C. H. Bennett et al., Phys. Rev. A 59, 1070 (1999).

[3] A. Carollo et al., Phys. Rev. A 64, 022318 (2001).