Generation of tunable wavelength coherent states and heralded single photons for quantum optics applications

Quantum optics experiments frequently involve interfering single photons and coherent states. In the case of multi-photon experiments this requires all photons to be frequency degenerate. We report a simple and practical approach to generate coherent states that can be readily tuned to any wavelength required, for example by non-degenerate photon pair creation. We demonstrate this by performing a two-photon (Hong–Ou–Mandel) interference experiment between a coherent state and a pure heralded single photon source. Neither interfering photon passes through a spectral filter, the coherent state is constrained by the pump and seed lasers and the heralded photon exploits non-local filtering. We expect that such an approach can find a wide range of applications in photonic based quantum information science.