Fast quantum-enhanced imaging with visible-wavelength entangled photons.

Quantum resources can provide supersensitive performance in optical imaging. Detecting entangled photon pairs from spontaneous parametric down conversion (SPDC) with single-photon avalanche diode (SPAD) image sensor arrays (ISAs) enables practical wide-field quantum-enhanced imaging. However, matching the SPDC wavelength to the peak detection efficiency range of complementary metal-oxide-semiconductor (CMOS) compatible mass-producible SPAD-ISAs has remained technologically elusive, resulting in low imaging speeds to date. Here, we show that a recently developed visible-wavelength entangled photon source enables high-speed quantum imaging. By operating at high detection efficiency of a SPAD-ISA, we increase acquisition speed by more than an order of magnitude compared to previous similar quantum imaging demonstrations. Besides being fast, the quantum-enhanced phase imager operating at short wavelengths retrieves nanometer scale height differences, tested by imaging evaporated silica and protein microarray spots on glass samples, with sensitivity improved by a factor of 1.351 ± 0.004 over equivalent ideal classical imaging. This work represents an important stepping stone towards scalable real-world quantum imaging advantage, and may find use in biomedical and industrial applications as well as fundamental research.

Multipass wide-field phase imager.

Advances in optical imaging always look for an increase in sensitivity and resolution among other practicability aspects. Within the same scope, in this work we report a versatile interference contrast imaging technique, with high phase sensitivity and a large field-of-view of several mm2. Sensitivity is increased through the use of a self-imaging non-resonant cavity, which causes photons to probe the sample in multiple rounds before being detected, where the configuration can be transmissive or reflective. Phase profiles can be resolved individually for each round thanks to a specially designed single-photon camera with time-of-flight capabilities and true pixels-off gating. Measurement noise is reduced by novel data processing combining the retrieved sample profiles from multiple rounds. Our protocol is especially useful under extremely low light conditions as required by biological or photo-sensitive samples. Results demonstrate more than a four-fold reduction in phase measurement noise, compared to single round imaging, and values close to the predicted sensitivity in case of the best possible cavity configuration, where all photons are maintained until n rounds. We also find good agreement with the theoretical predictions for low number of rounds, where experimental imperfections would play a minor role. The absence of a laser or cavity lock-in mechanism makes the technique an easy to use inspection tool.

A quantum-enhanced wide-field phase imager.

Quantum techniques can be used to enhance the signal-to-noise ratio in optical imaging. Leveraging the latest advances in single-photon avalanche diode array cameras and multiphoton detection techniques, here, we introduce a supersensitive phase imager, which uses space-polarization hyperentanglement to operate over a large field of view without the need of scanning operation. We show quantum-enhanced imaging of birefringent and nonbirefringent phase samples over large areas, with sensitivity improvements over equivalent classical measurements carried out with equal number of photons. The potential applicability is demonstrated by imaging a biomedical protein microarray sample. Our technology is inherently scalable to high-resolution images and represents an essential step toward practical quantum-enhanced imaging.