Berlin 2001 – scientific programme

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Q: Quantenoptik

Q 15: Quantum Information IV

Q 15.4: Talk

Tuesday, April 3, 2001, 18:15–18:30, H 3010

Compact All-Solid-State Source of Entangled Photons — •J. Volz, C. Kurtsiefer, and H. Weinfurter — LMU München, Sektion Physik

Entangled photons became important tools for experiments on the foundations of quantum mechanics and for the new field of quantum information. The most common way to create such photons at wavelengths in the red or near-infrared region is spontaneous parametric down conversion (SPDC). Most SPDC sources use large-frame Ar-ion lasers to pump a nonlinear optical crystal where entangled photon pairs are created.

Here we present a new system using a laser diode (λ=856 nm) that is frequency doubled using KNbO₃ in an external resonator. The second harmonic is used to pump a second resonator containing a BBO-crystal in which type-II SPDC takes place. With this compact and inexpensive system we were able to create coincidence rates that are comparable with those of usual experiments. In a first demonstration we obtained about 10000 coincidences/sec and a polarization correlation of >94.7% in all bases. This shows that our setup is a good alternative source of entangled photons for a variety of experiments and possible applications of quantum information.