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Q: Quantenoptik und Photonik

Q 2: Quanteninformation I

Q 2.2: Vortrag

Montag, 22. März 2004, 14:15–14:30, HS 101

Witness Operators versus Bell Inequalities — •Philipp Hyllus, Otfried Gühne, Dagmar Bruß, Maciej Lewenstein, and Anna Sanpera — Institut für Theoretische Physik, Universität Hannover, 30167 Hannover

Quantum states that violate Bell inequalities cannot be described by a local hidden variable model. Witness operators provide a conceptually different method for the detection of entanglement in quantum systems. In general, the set of mixed quantum states that violate a Bell inequality is smaller than the set of states which are detected by a witness: even for 2-qubit systems there exist mixed entangled states that admit a local hidden variable model. We investigate the relation between witness operators and Bell inequalities for 2 qubits. We show how witness operators can be transformed to detect only states violating a Bell inequality, and demonstrate that known Bell inequalities correspond to non-optimal witness operators.