Quantum imaging with a photon counting camera

David McFadden, Rainer Heintzmann

Spatially entangled photon pairs (biphotons) generated by spontaneous parametric down-conversion offer unique opportunities for quantum imaging, but image-plane biphoton correlations are difficult to observe with camera-based detectors. Previous camera-based biphoton imaging experiments have relied on photon-counting detection, which necessitates operation deep in the photon-sparse regime and requires extremely low dark rates. Here, we demonstrate the detection of spatial biphoton joint probability distributions in both the image plane and the pupil plane (also termed "near-field plane" and "far-field plane" respectively) using a conventional scientific CMOS camera operated in linear mode. We work at mesoscopic intensity levels, corresponding to a photon flux approximately four orders of magnitude higher than typical photon-counting approaches. From the measured image- and pupil plane correlations, we observe position and momentum correlations consistent with an EPR-type entanglement witness. A tailored correlation analysis suited for image plane imaging suppresses detector artifacts and intensity fluctuations, enabling acquisition with significantly fewer frames. Our results demonstrate that spatially entangled-light imaging can be performed efficiently with standard imaging hardware, extending quantum imaging techniques beyond the photon-counting regime.

Gabriela Barreto Lemos, Victoria Borish, Garrett D. Cole +3 more

Joachim von Zanthier, C. Thiel, Thierry Bastin +2 more

Osian Wolley, Thomas Gregory, Sebastian M. J. Beer +2 more

Classical light sources emit a randomly-timed stream of individual photons, the spatial distribution of which can be detected with a camera to form an image. Quantum light sources, based on parametric down conversion, emit photons as correlated photon-pairs. The spatial correlations between the photons enables imaging systems where the preferential selection of photon-pairs allows for enhancements in the noise performance over what is possible using classical light sources. However, until now the technical challenge of measuring, and correlating both photons has led to system complexity. Here we show that a camera capable of resolving the number of individual photons in each pixel of the detector array can be used to record an image formed from these photon-pair events and hence achieve a greater contrast than possible using a classical light source. We achieve an enhancement in the ratio of two-photon events compared to one-photon events using spatially correlated SPDC light compared to uncorrelated illumination by a LED. These results indicate the potential advantages of using photon counting cameras in quantum imaging schemes and these advantages will further increase as the technology is developed. Operating in photon sparse regimes such systems have potential applications in low-light microscopy and covert imaging.

Ronald E. Meyers, Keith S. Deacon, Yanhua H. Shih

Distinct from previous principle-demonstrations, this practical quantum ghost imaging experiment presents the first set of two-photon images captured by a photon counting CCD camera by means of jointly counting 'reflected' photons from the object. In fact, the CCD camera was not 'looking' at the object at all. Rather, the CCD camera was facing the chaotic light source. The output of the CCD camera was used for coincidence registration of the two-photon joint-detection events with another photon counting detector which simply collects all randomly reflected photons from the surface of the object. It is also interesting to find that the observed two-photon images are 'distortion-free', i.e., any disturbances made along the light path has no effect on the quality of the image. These experimental observations are not only useful for practical field-applications, but also important from fundamental point of view. The experiment evidences a rejection of the 'projection shadow' idea in a non-deniable way and further explores the two-photon interference nature of thermal light ghost imaging.

Edoardo Charbon A