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Q: Fachverband Quantenoptik und Photonik

Q 50: Quantum information: Concepts and methods III

Q 50.3: Vortrag

Donnerstag, 20. März 2014, 17:00–17:15, Kinosaal

The Cauchy-Schwarz inequality: a powerful tool to detect entanglement — •Sabine Wölk and Otfried Gühne — Department Physik, Universität Siegen, 57068 Siegen, Germany

Entanglement is an important resource for quantum cryptography, quantum computing and quantum metrology. So far, no entanglement criteria exist, which are necessary and sufficient for all states. Therefore, many different criteria coexist. Some of them are in the form of inequalities of expectation values. These criteria are especially useful for experimental application. In this talk, we show how to derive such entanglement criteria by using two non-hermitian operators per subsystems and the help of the Cauchy-Schwarz inequality. In this way, new criteria and already existing criteria can be proven. In the bipartited case the collectivity of criteria derived with Cauchy-Schwarz are closely connected to the PPT-criterion. However, our criteria do not require a complete state tomography, a few measurement direction are sufficient. Furthermore, in the multipartite case, our criteria can also detect entangled states, which are biseparable under every bipartition and can therefore not be detected by the PPT-criterion.