Single Photon Detection Using Optical Heterodyne Interferometry

The coherent coupling between an electro-magnetic laser field and the axion or axion-like particle field inside a strong magnetic field is utilized by the ALPS collaboration to search for axions and axion-like particles. The proposed heterodyne detection method uses this coherence to search for a signal in a shot noise limited local oscillator field. This method has a high quantum efficiency and avoids typical limitations due to dark count rates and offers an improvement over classical photon counting detection methods. We built a testbed to study and develop this sensing scheme for ALPS. Our initial results of an equivalent dark count rate of better than $10^{-6}$/s and successful test experiments detecting photons at a rate of $10^{-2}$/s will be presented. We will also discuss potential future improvements.