Quantum states from parametric downconversion

For more than a decade, spontaneous parametric downconversion is the synonym for generation of entangled photon pairs. The applications include linear optical quantum computing, long distance quantum communication and quantum cryptography.

In our lab we use type II downconversion sources embedded in a Sagnac interferometer. Such sources are very versatile: by only changing the temperature of the nonlinear crystal one can tune the wavelength of the emitted photons for nanometers.

We create high-fidelity (HV + exp(iΦ) VH)/√2 entangled states and can operate our sources in cw and pulsed picosecond regime. In picosecond regime these sources are suitable for interaction with photons emitted for example from quantum dots.

Pulsed Sagnac source of polarization entangled photon pairs
A. Predojevic, S. Grabher and G.Weihs (Optics Express 20, 25022-25029, 2012)