Frankfurt 2006 – wissenschaftliches Programm

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Q: Quantenoptik und Photonik

Q 45: Nichtlineare optische Effekte und Lichtquellen I

Q 45.6: Vortrag

Mittwoch, 15. März 2006, 12:25–12:40, H14

Optimization of a picosecond-pumped source of polarization entangled photons based on spontaneous parametric down conversion intended for investigations in quantum communication — •Martin Ostermeyer, Sebastian Bange, and Nino Walenta — Universität Potsdam, Institut für Physik, 14469 Potsdam

A source of entangled photons generated by spontaneous parametric down-conversion was set up. This was achieved by pumping a BBO crystal with pulses of 8 ps duration at 355 nm. Conceptual aspects in the setup of the source for applications in quantum communication are addressed. For example an increase of the S-parameter in a CHSH type Bell equation from 2.489 to 2.681 resulted by the application of single mode instead of multi mode fiber coupling for the single photon detectors. Problematic aspects of such a source for protocols in quantum cryptography using entangled photon pairs in specific are considered. Especially higher order terms some times addressed as stimulated emission of entangled photons are considered in our ultra short pulse pumped regime. The distribution of the probability of the number of these pairs per pulse follows a poisson-like distribution.

The interference of the photons at a non-polarizing beam splitter as a first building block of a quantum cryptography protocol using entangled photons is realized and investigated under multimode and single mode coupling of the detectors. The required precision in the path length difference of the two photons is discussed with regard to the bandwidth of the source.