Resolution of Quantum Imaging with Undetected Photons

Quantum imaging with undetected pho-tons is a recently introduced technique that goes significantly beyond what was previously possible. In this technique, im-ages are formed without detecting the light that interacted with the object that is im-aged. Given this unique advantage over the existing imaging schemes, it is now of utmost importance to understand its res-olution limits, in particular what governs the maximal achievable spatial resolution. We show both theoretically and exper-imentally that the momentum correlation between the detected and undetected pho-tons governs the spatial resolution - a stronger correlation results in a higher res-olution. In our experiment, the momen-tum correlation plays the dominating role in determining the resolution compared to the effect of diffraction. We find that the resolution is determined by the wavelength of the undetected light rather than the wavelength of the detected light. Our re-sults thus show that it is in principle pos-sible to obtain resolution characterized by a wavelength much shorter than the de-tected wavelength.