High efficiency single photon detection via frequency up-conversion

We propose a method of single photon detection of infrared (IR) photons at potentially higher efficiencies and lower noise than allowed by traditional IR band avalanche photodiodes (APDs). By up-converting the photon from the IR, e.g. 1550 nm, to a visible wavelength in a nonlinear crystal, we can utilize the much higher efficiency of silicon APDs at these wavelengths. We have used a periodically poled lithium niobate (PPLN) crystal and a pulsed 1064 nm Nd:YAG laser to perform the up-conversion to a 631 nm photon. We observed conversion efficiencies as high as similar to80%, and demonstrated scaling down to the single photon level while maintaining a background of 3 x 10(-4) dark counts per count. We also propose a 2-crystal extension of this scheme, whereby orthogonal polarizations may be up-converted coherently, thus enabling complete quantum state transduction of arbitrary states.