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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Quantum imaging and spatial entanglement characterization with an EMCCD camera

Matthew C. Reichert, Hugo Defienne, Xiaohang Sun, Jason W. Fleischer

Published May 8, 2017• 0 citations
Publisher

Abstract

We utilize a single-photon sensitive electron multiplying CCD camera as a massively parallel coincidence counting apparatus to study spatial entanglement of photon pairs. This allows rapid measurement of transverse spatial entanglement in a fraction of the time required with traditional point-scanning techniques. We apply this technique to quantum experiments on entangled photon pairs: characterization of the evolution of entanglement upon propagation, and measurement of one- and two-photon portions of the state transmitted through non-unitary (lossy) objects, and quantum phase imaging.

DOI
10.1117/12.2264864

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We utilize a single-photon sensitive electron multiplying CCD camera as a massively parallel coincidence counting apparatus to study spatial entanglement of photon pairs. This allows rapid measurement of transverse spatial entanglement in a fraction of the time required with traditional point-scanning techniques. We apply this technique to quantum experiments on entangled photon pairs: characterization of the evolution of entanglement upon propagation, and measurement of one- and two-photon portions of the state transmitted through non-unitary (lossy) objects, and quantum phase imaging.
Entangled photons have the remarkable ability to be more sensitive to signal and less sensitive to noise than classical light. Joint photons can sample an object collectively, resulting in faster phase accumulation and higher spatial resolution, while common components of noise can be subtracted. Even more, they can accomplish this while physically separate, due to the nonlocal properties of quantum mechanics. Indeed, nearly all quantum optics experiments rely on this separation, using individual point detectors that are scanned to measure coincidence counts and correlations. Scanning, however, is tedious, time consuming, and ill-suited for imaging. Moreover, the separation of beam paths adds complexity to the system while reducing the number of photons available for sampling, and the multiplicity of detectors does not scale well for greater numbers of photons and higher orders of entanglement. We bypass all of these problems here by directly imaging collinear photon pairs with an electron-multiplying CCD camera. We show explicitly the benefits of quantum nonlocality by engineering the spatial entanglement of the illuminating photons and introduce a new method of correlation measurement by converting time-domain coincidence counting into spatial-domain detection of selected pixels. We show that classical transport-of-intensity methods are applicable in the quantum domain and experimentally demonstrate nearly optimal (Heisenberg-limited) phase measurement for the given quantum illumination. The methods show the power of direct imaging and hold much potential for more general types of quantum information processing and control.
Abstract Losses should be accounted for in a complete description of quantum imaging systems, and yet they are often treated as undesirable and largely neglected. In conventional quantum imaging, images are built up by coincidence detection of spatially entangled photon pairs (biphotons) transmitted through an object. However, as real objects are non-unitary (absorptive), part of the transmitted state contains only a single photon, which is overlooked in traditional coincidence measurements. The single-photon part has a drastically different spatial distribution than the two-photon part. It contains information about both the object, and, remarkably, the spatial entanglement properties of the incident biphotons. Here, we image the one- and two-photon parts of the transmitted state using an electron multiplying CCD array, treating it both as a traditional camera and as a massively parallel coincidence counting apparatus, and demonstrate agreement with theoretical predictions of non-unitary quantum optics. This work may prove useful for photon-number imaging and may lead to techniques for entanglement characterization that do not require coincidence measurements.
The light produced by parametric down-conversion shows strong spatial entanglement that leads to violations of EPR criteria for separability. Historically, such studies have been performed by scanning a single-element, single-photon detector across a detection plane. Here we show that modern electron-multiplying charge-coupled device cameras can measure correlations in both position and momentum across a multi-pixel field of view. This capability allows us to observe entanglement of around 2,500 spatial states and demonstrate Einstein–Podolsky–Rosen type correlations by more than two orders of magnitude. More generally, our work shows that cameras can lead to important new capabilities in quantum optics and quantum information science. Measuring the entanglement between down-converted photons is central to many quantum optical experiments, and is normally performed by scanning detectors stepwise across a plane. Edgaret al. use a CCD camera to measure the entire entangled light field, finding strong correlations in position and momentum.