Sci. Adv. 6, eaay2652 (2020)

The spatial correlations of entangled photon pairs lie at the heart of many quantum applications — most famously in secure communication protocols. But they can also be used to distinguish a signal from a background, which can be extended to imaging applications. Thomas Gregory and colleagues have now implemented a full-field quantum imaging method where correlations help separate an object from a thermal background.

Gregory and colleagues illuminated an object — the silhouette of a bird — with one half of an entangled photon pair while the other passed through free space. The two photons arrived at distinct areas of the electron-multiplying charge-coupled device camera, and the team could then use a simple AND operation between pixels to learn which signals came from the quantum source and which were background or noise — even when they overlaid a cage illuminated by an uncorrelated thermal light source onto the bird image. This contrast enhancement through quantum illumination could be extended to other applications like LIDAR.