A space-suitable, high brilliant entangled photon source for satellite based quantum key distribution

Quantum Key Distribution (QKD) will be the first applications for quantum technologies, addressing information security needs by providing a tool for quantum encryption. An Entangled Photon Source EPS, the key building block for QKD, is presented that is based on a non-linear, Spontaneous Parametric Down Conversion SPDC process in a temperature controlled ppKTP crystal that is double-side pumped at 405 nm in a sagnac interferometer setup. The polarization entangled photons are emitted at 810 nm and at a rate of up to ca. 300k per second at 8 mW pumping power. Visibilities in the HV and the DA polarization base in the range of 97-99% have been measured. The EPS integration was realized in a ruggedized, minimized setup to prove space-suitability during thermal and mechanical environmental testing.