Entanglement based Spontaneous Parametric Down Conversion sources for Quantum Key Distribution applications

Spontaneous Parametric Down-Conversion (SPDC) is a phenomenon that allows the generation of photon pairs, rather than single photons, by injecting light from a pump laser into a non-linear crystal. The source under test emits pairs of photons entangled both in number and polarization in two different directions, called idler and signal. When dealing with entangled states emitted by an SPDC source, we can enhance security in transmitting information by leveraging the correlated information between the emitted photons. In our work, we investigate the entanglement of the source by using superconducting photon number resolving detectors and SNSPDs, conditioning the detection events on the signal path to the detection events on the idler path. The results achieved are promising to explore applications for low-noise Quantum Key Distribution (QKD) and communication via entanglement.