New Results on Single-Photon Up-Conversion

The process of up-conversion is shown to enable superior single-photon detectors in the infrared, compared to InGaAs and germanium Avalanche Photodiodes (APDs) (normally used for IR single photon detection). After up-converting an infrared photon to a visible one in a non-linear crystal–Periodically Poled Lithium Niobate (PPLN)–we use a silicon APD to efficiently detect the frequency up-shifted IR photon. We have demonstrated this process at the “high-intensity” level and at the single-photon level, where the up-converted state is effectively a superposition of the single photon Fock state and the vacuum state. We achieve an 80% conversion efficiency over the width of the pulse, and show that this process is coherent, a necessary ingredient for many applications.