We emulate quantum-enhanced telescopy through interconnected interferometers and demonstrate experimental progress toward optimally recovering the visibility amplitude of a source and displaying an advantage of using distributed single photons over a weak coherent source.
Quantum telescopy, proposed by Grottesman et al., uses spatially entangled single-photon states to modify HBT stellar interferometry, potentially surpassing Michelson interferometry in resolution without baseline limits. However, finite source bandwidth, non-unit efficiency, detector response times, and celestial light bandwidth all affect its effectiveness. In this work, we consider a spatially entangled singe-photon state generated by beam-splitting a practical anti-bunched photon source from resonance fluorescence, which is a common method of generating single-photon states, and evaluate the signal level in quantum telescopy with inclusion of imperfection of detection system and finite bandwidth of celestial light. Here, given the incoming light, we optimize the parameters of the anti-bunched photon source and the detector system for the best signal-to-noise ratio (SNR), which can match that of the Michelson method in the ideal case but is always smaller in the realistic case. Alternatively, weak coherent states from heavily attenuated lasers can replace the entangled single-photon state but suffer low signal level, similar to HBT method. We find that the SNR with a realistic anti-bunched source for producing the reference fields can still beat the SNR of the coherent state scheme in the weak incoming field limit. The optimized parameters for the anti-bunched source and detection system will be a guide for future experimental endeavor.
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.