Licentiate Thesis: Entangled source for quantum information

A spontaneous parametric down conversion based source which produces 780 nm and 1550 nm polarization-entangled photon pairs has been developed and characterized in order to use for  quantum communication experiments. These two wavelengths are of great importance for long distance quantum communication of view. The780 nm wavelength corresponds to D2 optical transition for rubidium-87 atom which is used for building quantum memories, and the 1550 nm wavelength corresponds to the low-loss telecom window well adapted to long distance optical communications.

The entangled photons were generated by pumping a 15 mm long periodically poled Potassium Titanyl Phosphate crystal (ppKTP) with a 518.9 nm stabilized laser diode inside a Sagnac interferometric configuration.

The source produces two-qubit maximally entangled state with high fidelity of 96.95%.  We have tested the violation of Bell inequality and obtained a violation of 2.765 > 2. In addition, we also developed a characterization setup for testing single photon detectors based on nanowires superconductors (SSPD) to determine and calibrate their quantum efficiency, dark counts and time jitter.