Passive optical superresolution at the quantum limit

TL;DR

This review discusses quantum measurement strategies that surpass classical limits in optical resolution, enabling superresolution imaging at the quantum limit across various applications.

Contribution

It summarizes the theoretical framework and experimental advances in quantum optical measurement techniques that achieve superresolution beyond the diffraction limit.

Findings

Quantum measurement strategies can beat classical resolution limits.

Optimal detection methods like spatial-mode demultiplexing attain quantum bounds.

Recent experiments approach quantum-limited resolution in imaging applications.

Abstract

For more than a century, the diffraction limit has defined the resolution achievable by passive optical imaging systems. Although some resolution improvement can be gained through classical data processing of the image, it is limited by the noise arising from quantum nature of light. Minimizing the effect of this noise requires quantum treatment of optical imaging. By reformulating imaging as a problem of quantum measurement and estimation, it becomes possible to identify optimal detection strategies that recover spatial information previously thought inaccessible. This review summarizes the theoretical framework that underpins this development, from the formulation of quantum Cram\'er-Rao bounds and Chernoff bounds to the construction of receivers that attain them, such as those based on spatial-mode demultiplexing. We show how these methods can beat conventional imaging in the classification, localization, and imaging of sub-Rayleigh incoherent sources. We then discuss extensions to multiparameter and partially coherent scenarios, and highlight the unifying connections between estimation and discrimination tasks. Finally, we survey recent experimental demonstrations that approach quantum-limited resolution and outline emerging applications in microscopy, astronomy, and optical sensing.