Lost photon enhances superresolution

TL;DR

This paper demonstrates that measuring fewer photons than available in an entangled state can lead to even higher resolution in quantum imaging, surpassing traditional n-photon correlation methods.

Contribution

It reveals that ignoring one photon in an entangled n-photon state can further narrow the PSF, offering a new approach to enhance quantum imaging resolution.

Findings

Measuring (n-1)-photon coincidences yields narrower PSF than n-photon correlations.

Conditional resolution enhancement is achievable by detecting one photon outside the imaging area.

Proposed practical scheme enables observation and utilization of this superresolution effect.

Abstract

Quantum imaging can beat classical resolution limits, imposed by diffraction of light. In particular, it is known that one can reduce the image blurring and increase the achievable resolution by illuminating an object by entangled light and measuring coincidences of photons. If an $n$-photon entangled state is used and the $n$th-order correlation function is measured, the point-spread function (PSF) effectively becomes $\sqrt n$ times narrower relatively to classical coherent imaging. Quite surprisingly, measuring $n$-photon correlations is not the best choice if an $n$-photon entangled state is available. We show that for measuring $(n-1)$-photon coincidences (thus, ignoring one of the available photons), PSF can be made even narrower. This observation paves a way for a strong conditional resolution enhancement by registering one of the photons outside the imaging area. We analyze the conditions necessary for the resolution increase and propose a practical scheme, suitable for observation and exploitation of the effect.