Entangled biphoton sources exhibit nonclassical characteristics and have been applied to imaging techniques such as ghost imaging, quantum holography, and quantum optical coherence tomography. The development of wide-field quantum imaging to date has been hindered by low spatial resolutions, speeds, and contrast-to-noise ratios (CNRs). Here, we present quantum microscopy by coincidence (QMC) with balanced pathlengths, which enables super-resolution imaging at the Heisenberg limit with substantially higher speeds and CNRs than existing wide-field quantum imaging methods. QMC benefits from a configuration with balanced pathlengths, where a pair of entangled photons traversing symmetric paths with balanced optical pathlengths in two arms behave like a single photon with half the wavelength, leading to a two-fold resolution improvement. Concurrently, QMC resists stray light up to 155 times stronger than classical signals. The low intensity and entanglement features of biphotons in QMC promise nondestructive bioimaging. QMC advances quantum imaging to the microscopic level with significant improvements in speed and CNR toward the bioimaging of cancer cells. We experimentally and theoretically prove that the configuration with balanced pathlengths illuminates an avenue for quantum-enhanced coincidence imaging at the Heisenberg limit.
Entangled biphoton sources exhibit nonclassical characteristics and have been applied to imaging techniques such as ghost imaging, quantum holography, and quantum optical coherence tomography. The development of wide-field quantum imaging to date has been hindered by low spatial resolutions, speeds, and contrast-to-noise ratios (CNRs). Here, we present quantum microscopy by coincidence (QMC) with balanced pathlengths, which enables super-resolution imaging at the Heisenberg limit with substantially higher speeds and CNRs than existing wide-field quantum imaging methods. QMC benefits from a configuration with balanced pathlengths, where a pair of entangled photons traversing symmetric paths with balanced optical pathlengths in two arms behave like a single photon with half the wavelength, leading to a two-fold resolution improvement. Concurrently, QMC resists stray light up to 155 times stronger than classical signals. The low intensity and entanglement features of biphotons in QMC promise nondestructive bioimaging. QMC advances quantum imaging to the microscopic level with significant improvements in speed and CNR toward the bioimaging of cancer cells. We experimentally and theoretically prove that the configuration with balanced pathlengths illuminates an avenue for quantum-enhanced coincidence imaging at the Heisenberg limit.
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.
Entangled photons enable quantum imaging to surpass classical limits in resolution and noise. To address long-standing challenges in quantum imaging (such as low signal-to-noise, limited resolvable pixels, and difficulty imaging biological samples), we present imaging by coincidence from entanglement (ICE). ICE leverages spatial and polarization entanglement to enhance resolution, support biological imaging, and quantify birefringence properties. Polarization entanglement enables remote, quantitative measurement of both phase retardation and principal axis orientation without changing input polarization. ICE achieves up to 25-fold stray light suppression relative to classical imaging. We further introduce wide-field quantum microscopy by coincidence (QMC) using symmetric, balanced paths to achieve Heisenberg-limited super-resolution, with up to 155-fold suppression of stray light and improved speed and contrast-to-noise ratio. Together, QMC and ICE represent significant advances in quantum bioimaging, offering low-light, high-resolution, and noninvasive imaging capabilities with potential impact in life sciences and remote sensing.
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.
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)
Correct biological interpretation from cell imaging can be achieved only if the observed phenomena proceed with negligible perturbation from the imaging system. Herein, we demonstrate microscopic images of breast cancer cells created by the fluorescence selectively excited in the process of entangled two-photon absorption in a scanning microscope at an excitation intensity orders of magnitude lower than that used for classical two-photon microscopy. Quantum enhanced entangled two-photon microscopy has shown cell imaging capabilities at an unprecedented low excitation intensity of ∼3.6 × 10 7 photons/s, which is a million times lower than the excitation level for the classical two-photon fluorescence image obtained in the same microscope. The extremely low light probe intensity demonstrated in entangled two-photon microscopy is of critical importance to minimize photobleaching during repetitive imaging and damage to cells in live-cell applications. This technology opens new avenues in cell investigations with light microscopy, such as enhanced selectivity and time–frequency resolution.
Quantum imaging is emerging as a transformative approach for biomedical applications, applying nonclassical properties of light, such as entanglement, squeezing, and quantum correlations, to overcome fundamental limits of conventional techniques. These methods promise superior spatial resolution, enhanced signal-to-noise ratios, improved phase sensitivity, and reduced radiation dose, for potentially safer and more precise imaging for delicate biological samples. Here, we present an overview of quantum optical biomedical imaging technologies as well as quantum-inspired imaging methods, including quantum optical coherence tomography, quantum optical microscopy, ghost imaging, multi-parameter quantum imaging, and imaging with quantum-grade cameras. We describe the operating principles, biomedical applications, and unique advantages of each approach, along with the specific challenges for their translation into real-life practice. This review aims to guide future research toward advancing quantum imaging from experimental demonstrations to impactful biomedical tools.