Dresden 2011 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 7: Quantum Information: Concepts and Methods 1

Q 7.9: Vortrag

Montag, 14. März 2011, 12:30–12:45, SCH A118

Entanglement verification with realistic measurement devices via squash models — •Tobias Moroder¹, Otfried Gühne^1,2, Normand Beaudry³, Marco Piani⁴, and Norbert Lütkenhaus⁴ — ¹Institute for Quantum Optics and Quantum Information, Innsbruck, Austria — ²Department of Physics, University of Siegen, Germany — ³Institute for Theoretical Physics, ETH Zurich, Switzerland — ⁴Institute for Quantum Computing, Waterloo, Canada

Many protocols and experiments in quantum information science are described in terms of simple measurements on qubits. However, in a real implementation, the exact description is more difficult and more complicated observables are used. The question arises whether a claim of entanglement in the simplified description still holds, if the difference between the realistic and simplified model is taken into account.

We show that a positive entanglement statement remains valid if a certain linear map connecting the two measurement models exists. For entanglement verification this map only needs to be positive, but not necessarily completely positive as required in tasks like quantum key distribution, where this idea called squash model is already quite common. However this offers the possibility to employ this technique even for measurement setups which do not possess a completely positive squash model. The well-known polarization measurement using only threshold detectors, which is extensively used in optical experiments, represents a physical relevant example for which this new technique can indeed be applied.