Single Photon Imaging Overcomes Diffraction Limit

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Arxiv.org paper "Super-Resolution Quantum Imaging at the Heisenberg Limit" by Manuel Unternährer, Bänz Bessire, Leonardo Gasparini, Matteo Perenzoni, and André Stefanov from FBK, Italy and Institute of Applied Physics, University of Bern, Switzerland combines an entangled photons light source and a single-photon imager to overcome diffraction resolution limit:

"Quantum imaging exploits the spatial correlations between photons to image object features with a higher resolution than a corresponding classical light source could achieve. Using a quantum correlated N-photon state, the method of optical centroid measurement (OCM) was shown to exhibit a resolution enhancement by improving the classical Rayleigh limit by a factor of 1/N. In this work, the theory of OCM is formulated within the framework of an imaging formalism and is implemented in an exemplary experiment by means of a conventional entangled photon pair source. The expected resolution enhancement of a factor of two is demonstrated. The here presented experiment allows for single-shot operation without scanning or iteration to reproduce the object in the image plane. Thereby, photon detection is performed with a newly developed integrated time-resolving detector array. Multi-photon interference effects responsible for the observed resolution enhancement are discussed and possible alternative implementation possibilities for higher photon number are proposed."


"In conclusion, our theoretical and experimental results demonstrate that quantum states of light showing super-resolution at the Heisenberg limit can be engineered. By limiting the Rayleigh resolution in low NA single-lens imaging, different light sources are compared in their ability to transmit spatial information. The OCM biphoton state used in our experiment shows a resolution enhancement close to a factor of two and is comparable to imaging at half the wavelength. For high NA systems, where the classical resolution is mainly limited by the wavelength, or for higher photon number N, theory suggests the possibility to have sub-wavelength image features present in the centroid coordinate. A full vectorial field analysis in contrast to the scalar approximations has yet to show the advantage in the limit of high NA.

Integrated single-photon detector arrays as presented here will certainly give rise to more experiments and applications in the field of quantum imaging. While the device in this work has non-optimal detection efficiency at the used wavelength, a speed up in acquisition time and higher photon number correlation measurement is expected in more optimized settings.
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