Toward Quantum-Enhanced Interferometric Telescopy

We emulate one version of quantum-enhanced telescopy through cross-connected Hong-Ou-Mandel interferometers that are fed with both astronomical and terrestrial photons. We use spontaneous parametric down-conversion to produce two photons in different paths that represent our "astronomical" and "terrestrial" source. This allows us to take measurements on a system under the assumption that we have properly filtered an astronomical photon and also effectively increases our single photon rates for tabletop demonstration. To witness the desired fringes, we synchronize the photons' arrival time at each telescope to obtain two-photon interference, where we maximize the visibility to ensure high indistinguishability per telescope. From the interference fringes across telescopes we can determine the coherence between different pairs of telescopes. One benefit of using a distributed local oscillator over direct detection interference of the astronomical photons is the ability to match unbalanced telescope inputs, optimizing the visibility amplitude recovery. We also can compare different terrestrial sources, showing the advantage of single photons over a weak coherent source as the distributed local oscillator.