Demonstrating table-top interferometric imaging using a path-entangled single photon towards quantum telescopy

There have been several versions of optical wavelength astronomical imaging interferometers over the years, with the preferred form being Michelson direct detection (though Hanbury-Brown-Twiss is currently in revival). Even though it is prevalent in radio astronomy, using a common reference (e.g., a laser) is known to have a poor signal-to-noise ratio at visible wavelengths as the shot noise introduced by the reference overwhelms the considerably weaker signal collected by the telescopes. In 2012, a team of quantum physicists (Gottesman, Jennewein and Croke (GJC)) proposed a novel method for using a common optical reference that would abate the shot-noise issue: a path-entangled single-photon reference (i.e., a single photon that is split on a beam splitter). Transported to the various telescopes using a quantum network to overcome loss, the distributed single photon is then interfered with the optical field collected by the telescopes. Previously, we successfully demonstrated a proof-of-principle table-top experiment that implements the GJC protocol where we recovered the spatial autocorrelation of quasi-thermal double-slit sources in a single spectral-temporal mode where the single photon was produced by heralded parametric down conversion. Using quantum optics theory, we modeled our system and found good agreement allowing us to extend our model, and compare and contrast with similarly weak, non-single-photon reference sources (e.g., coherent states). Using the knowledge gained from this experiment, we document the plausibility of an on-sky measurement of the sun utilizing a similar phase reference.