Single Photon Source

In quantum information, we encode any information on to a qubit. For quantum communication, the most prevalent choice for a qubit is a single photon, with information encoded in the polarization states. To have a reliable quantum network we need a source that produces single photons on demand and so it is an essential component for the quantum network .  We exploit the principle of Spontaneous Parametric Down Conversion (SPDC) using Type II non linear crystals to convert blue light(~400nm) into red light(795nm).  To have single photons of red light tuned to AN atomic transition in Rubidium, we first generate blue light from red light using Second Harmonic Generation(SHG).  The blue light generated by SHG is then sent through the non linear crystal to get red single photons. However, the single photons generated using SPDC are not suited for storage because the frequency bandwidth of these single photons are not compatible for storage in any atomic memory. For this reason, the crystal is placed in an Optical Parametric Amplification(OPA) cavity to enhance the mode of the single photons coming out of the cavity. The source will be used to perform heralding experiments and to generate squeezed light as well as other experiments.