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Science Advances

Above-twofold quantum super-resolution microscopy enabled by multiple idler passes with entangled biphotons

Xin Tong, Zhe He, Yide Zhang, Wenyu Liu, Chien-Ying Huang, Lihong V. Wang

Published Jul 24, 2026• 0 citations
Publisher

Abstract

Spatial resolution defines the fundamental limit of how precisely optical imaging systems can distinguish details within an object. Recent advances in quantum imaging have surpassed classical resolution limits by exploiting entanglement. However, experimental demonstrations of quantum enhancement above two times using entangled biphotons have thus far been limited to nonimaging experiments that use replication of the object or nonlinearity-both are impractical and inefficient. Here, without resorting to either, we enhance the classical resolution using entangled photon pairs by either two- or fourfold in two system configurations. While the signal photons traverse the object-containing arm only once, the idler photons traverse the symmetric object-free arm either once or thrice. These experiments demonstrate a scalable route toward quantum-correlated super-resolution imaging, motivate theoretical exploration of the underlying mechanisms, and open opportunities for high-precision, low-illumination microscopy.

DOI
10.1126/sciadv.aea9457

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Spatial resolution defines the fundamental limit of how precisely optical imaging systems can distinguish details within an object. Recent advances in quantum imaging have surpassed classical resolution limits by exploiting entanglement. However, experimental demonstrations of quantum enhancement above two times using entangled biphotons have thus far been limited to nonimaging experiments that use replication of the object or nonlinearity-both are impractical and inefficient. Here, without resorting to either, we enhance the classical resolution using entangled photon pairs by either two- or fourfold in two system configurations. While the signal photons traverse the object-containing arm only once, the idler photons traverse the symmetric object-free arm either once or thrice. These experiments demonstrate a scalable route toward quantum-correlated super-resolution imaging, motivate theoretical exploration of the underlying mechanisms, and open opportunities for high-precision, low-illumination microscopy.
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Quantum super-resolution imaging provides a nonlabeling method to surpass the diffraction limit of imaging systems. This technique relies on measurement of the second-order correlation function and usually employs spatially entangled photon sources. We introduce recent methods that achieve spatial resolution enhancement through quantum approaches, particularly the imaging techniques utilizing biphoton states. The fundamental mechanisms are discussed in detail to explain why biphoton states enable super-resolution. Additionally, we introduce multiple algorithms that extract the correlation function from the readings of two-dimensional detectors. Several cases are reviewed to evaluate the advantages and prospects of quantum imaging, along with a discussion of practical developments and potential applications.
We use entangled photons as the light source in a normal microscope. Using this quantum illumination improves both the resolution and noise rejection in the image. The resolution of any classical imaging system is limited by the diffraction created by the finite size of the imaging lens. By using a light source that emits pairs of entangled photons and carefully controlling a camera that is capable of detecting single photons it is possible to observe these photons arriving two-by-two. Applying camera analysis software to log only these two-by-two events one can form an image from the mid-point (bisector) of each of these pair events. The image formed from the sum of all these bisectors has an improved resolution that surpasses the classical limit. Another advantage of using a quantum illumination is that it allows the two-by-two events from entangled photon pairs to be distinguished from background (classical) light and sensor noise. When processed in this way the resulting image is free of camera noise and any background light may be eliminated. The use of a quantum illumination protocol such as that used here results in the elimination of background light and therefore allows the development of the optical equivalent of quantum radar – a quantum enhanced LIDAR scheme. Using quantum illumination, combined with commercially available cameras that are sensitive to single photons creates a new approach to super-resolution and low noise microscopy. Imaging through noise with quantum illumination, T Gregory, P-A Moreau, E Toninelli, and M J Padgett, Science Advances 6, eaay2652 (2020) Resolution-enhanced quantum imaging by centroid estimation of biphotons, E Toninelli, P-A Moreau, T Gregory, A Mihalyi, M Edgar, N Radwell, and M J Padgett, Optica 6, 347-353 (2019)
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 NNN-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/N1/N1/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.
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.
We introduce quantum microscopy by coincidence (QMC) featuring balanced pathlengths, which facilitates super-resolution imaging at the Heisenberg limit, drastically boosting speed and contrast-to-noise ratio (CNR) compared to existing wide-field quantum imaging methods. QMC uses correlated photons traversing symmetric paths, behaving like a photon with half the wavelength for twice the resolution. It withstands 155 times stronger stray light than classical signals, promising non-destructive bioimaging. Our approach propels quantum imaging to microscopic scale by imaging cancer cells. Experimental and theoretical results endorse this balanced pathlength configuration as a path to quantum-enhanced coincidence imaging at the Heisenberg limit.