Cmos Camera Achieves Image-Plane Detection of Spatially Entangled Photon Pairs at 4 Orders of Magnitude Higher Flux
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The challenge of capturing subtle correlations between entangled photons has long limited the potential of advanced imaging techniques, but a new approach overcomes these hurdles. David McFadden and Rainer Heintzmann, from the Institute of Physical Chemistry and the Abbe Center respectively, alongside their colleagues, now successfully detect these entangled photon pairs using a standard scientific CMOS camera. This achievement represents a significant step forward because it allows researchers to work with much brighter light sources, approximately ten thousand times more intense than previously possible with conventional methods. By developing a tailored correlation analysis, the team reveals position and momentum correlations indicative of quantum entanglement, opening doors to more efficient and practical spatially resolved imaging beyond the limitations of single-photon detection. Spatially entangled photon pairs, generated by spontaneous parametric down-conversion, offer unique opportunities for quantum imaging, but observing image-plane biphoton correlations has historically been difficult with camera-based detectors. Previous experiments relied on photon-counting detection, necessitating operation in the photon-sparse regime and extremely low dark rates. This work demonstrates the detection of spatial biphoton joint probability distributions in both the image and pupil planes using a conventional scientific CMOS camera operated in linear mode, achieving this without single-photon counting and opening new avenues for more practical quantum imaging systems.
Entangled Light Imaging Beyond Photon Counting The team performs imaging using light from spontaneous parametric down-conversion at mesoscopic intensity levels, achieving a photon flux approximately four orders of magnitude higher than typical photon-counting approaches. From measurements of image and pupil plane correlations, they observe position and momentum correlations consistent with an EPR-type entanglement witness. A tailored correlation analysis suppresses detector artifacts and intensity fluctuations, enabling data acquisition with significantly fewer frames, demonstrating that spatially entangled-light imaging can be performed efficiently with standard imaging hardware, extending quantum imaging techniques beyond the photon-counting regime. This light consists of biphotons, which exhibit position correlation when they reach the detector in the image plane, allowing image reconstruction by detecting and registering these joint photon arrivals. This contrasts with classical imaging, where all arriving photons contribute equally to the image, and offers potential advantages in resolution, contrast, or information content compared to classical illumination. However, biphoton light is sensitive to optical loss and detector conditions, presenting experimental challenges. Detecting spatial correlations at the single-photon level is complicated by the readout noise of conventional CCD and CMOS cameras when operating in the single-photon regime, leading many experiments to rely on photon-counting detectors. Advances in active pixel sensor technology have led to scientific CMOS cameras with sub-electron readout noise, high quantum efficiency, and large pixel counts, but their use in biphoton imaging has largely been restricted to photon-counting-like operation at very low light levels. Here, the researchers demonstrate detection of spatial quantum correlations at photon fluxes of approximately 200 photons per pixel per frame, significantly exceeding the photon-sparse regime. The experimental setup involves a continuous-wave laser at 266nm illuminating a β-barium borate (BBO) crystal, configured for type-I spontaneous parametric down-conversion. A reflective long-pass filter removes the pump beam while transmitting the down-converted light. The resulting SPDC field is relayed using an infinite conjugate imaging configuration, beginning with a lens placed one focal length from the crystal. An adjustable iris defines the pupil plane, and a second lens images the crystal plane onto the camera sensor, completing the image plane configuration. To image the pupil plane, the second lens is replaced with a relay lens system, imaging the iris plane onto the camera sensor without moving the sensor. A band-pass filter with a central wavelength of 520nm is placed in the optical path. The sensitivity of biphoton correlations to loss is exploited as an experimental control, with a neutral density filter blocking 90% of the light to attenuate the signal. The researchers acquired data in both the image and pupil planes, measuring the width of the observed correlations and comparing the product of the inferred variances with the Heisenberg limit to assess the presence of EPR steering. While the image processing removes spurious correlations, potentially invalidating the variance estimation, the experiments provide an estimate of what would be obtained with appropriately shaped beams.
The team acquired 100 frames for each configuration, and the resulting images exhibit peaks diminished in the control experiment with attenuated light. They estimate the widths of the inference variances via a fit of a 2D Gaussian model, excluding the central pixel from the fit for the image plane data, performed over a circular central region 80 pixels in diameter. The resulting estimates demonstrate a violation of the Heisenberg limit, confirming the presence of spatial entanglement. They also investigated the influence of imaging parameters by repeating the experiment for different diameters of the iris aperture, finding that reducing the aperture broadens the correlation peak while decreasing its height. They have demonstrated the measurement of spatial biphoton joint probability distributions in both the image and pupil plane using a scientific CMOS camera.
Spatial Biphoton Correlations Detected with CMOS Camera Scientists achieved the detection of spatial biphoton joint probability distributions in both the image and pupil planes using a conventional scientific CMOS camera operating in linear mode, a significant advancement in quantum imaging.
The team measured photon fluxes approximately four orders of magnitude higher than those used in typical photon-counting approaches, reaching approximately 200 photons per pixel per frame, and successfully recovered spatial correlations in the image plane. Data shows clear position and momentum correlations consistent with an EPR-type entanglement witness, observed from the measured image and pupil plane correlations, confirming the quantum nature of the detected light. To validate the results, the team conducted control experiments by introducing a neutral density filter, reducing the biphoton arrival rate to approximately 25% while maintaining a comparable total photon flux, and observed a corresponding decrease in the correlation signal. This tailored correlation analysis, designed to suppress detector artifacts and intensity fluctuations, enabled acquisition with significantly fewer frames than previously required for similar experiments. The breakthrough delivers efficient spatially entangled-light imaging using standard imaging hardware, bypassing the limitations of the photon-sparse regime traditionally required for biphoton imaging.
Entangled Photon Correlations Imaged with Standard Camera Scientists have successfully detected spatial correlations within pairs of entangled photons, known as biphotons, using a standard scientific camera operating in conventional linear mode. This achievement circumvents the need for extremely low light levels and lengthy acquisition times that typically characterise photon-counting methods, instead working with significantly higher photon fluxes.
The team measured joint probability distributions of these photon pairs in both the image and pupil planes, revealing position and momentum correlations consistent with a form of quantum entanglement known as an EPR-type witness. These results demonstrate that imaging with entangled light can be performed efficiently with readily available imaging technology, expanding the scope of quantum imaging techniques beyond the limitations of single-photon detection. By operating in a mesoscopic intensity regime, the researchers avoided the severe limitations of photon-counting while maintaining the ability to capture multimode entanglement.
The team acknowledges that their variance estimation relies on approximations and that measurements were taken sequentially, potentially introducing a classical loophole, but the observed correlations nonetheless confirm the presence of spatial entanglement. Future work may focus on refining the measurement techniques and exploring simultaneous measurements to further validate these findings and enable faster, more scalable investigations of entangled-light imaging, ultimately providing a practical means to benchmark biphoton imaging systems. 👉 More information 🗞 Image-Plane Detection of Spatially Entangled Photon Pairs with a CMOS Camera 🧠 ArXiv: https://arxiv.org/abs/2512.24878 Tags: