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Laser & Photonics Review

Visualizing the Hardy's Paradox using Hyper‐Entanglement‐Assisted Ghost Imaging

Wuhong Zhang, Xiaodong Qiu, Dongkai Zhang, Lixiang Chen

Published Sep 10, 2023• 7 citations
Publisher

Abstract

Abstract The concept of quantum nonlocality, lying at the heart of quantum information science and technologies, is physically counter‐intuitive and mathematically elusive. Here, a hyper‐entanglement‐assisted ghost imaging system is designed to visualize the evidence of Hardy's paradox by capturing the purely nonlocal photonic events with a spatially resolved intensified charge‐coupled device (ICCD) camera. In the two‐photon polarization‐spatial‐mode hyper‐entangled state, spatial entanglement conveys the ghost images while polarization entanglement encodes the imaging channels in the logical structure of Hardy's nonlocality proof. Then whether the single ghost image of a skull‐shape object is observed or not can be a direct yet intuitive signature to support or defy quantum mechanics. Moreover, the degree of the violation of locality can be characterized by the contrast‐to‐noise ratio of ghost images macroscopically, and the nonlocal behavior of violating the locality microscopically at the single‐pixel level with a reasonable confidence level of 75% is also achieved. The proposed strategy not only sheds new light on the fundamental issue of quantum mechanics, but also holds promise for developing hyper‐entanglement‐based quantum imaging technology.

DOI
10.1002/lpor.202200865

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Abstract The concept of quantum nonlocality, lying at the heart of quantum information science and technologies, is physically counter‐intuitive and mathematically elusive. Here, a hyper‐entanglement‐assisted ghost imaging system is designed to visualize the evidence of Hardy's paradox by capturing the purely nonlocal photonic events with a spatially resolved intensified charge‐coupled device (ICCD) camera. In the two‐photon polarization‐spatial‐mode hyper‐entangled state, spatial entanglement conveys the ghost images while polarization entanglement encodes the imaging channels in the logical structure of Hardy's nonlocality proof. Then whether the single ghost image of a skull‐shape object is observed or not can be a direct yet intuitive signature to support or defy quantum mechanics. Moreover, the degree of the violation of locality can be characterized by the contrast‐to‐noise ratio of ghost images macroscopically, and the nonlocal behavior of violating the locality microscopically at the single‐pixel level with a reasonable confidence level of 75% is also achieved. The proposed strategy not only sheds new light on the fundamental issue of quantum mechanics, but also holds promise for developing hyper‐entanglement‐based quantum imaging technology.
The concept of quantum entanglement and hyper-entanglement, lying at the heart of quantum information science and technologies, is physically counter-intuitive and mathematically elusive. We design a polarization-encoded ghost imaging system based on the frame of Hardy nonlocality paradox to visualize the evidence of quantum hyper-entanglement by capturing purely nonlocal photonic events. In two-photon polarization-spatial-mode hyper-entangled state, spatial entanglement con-veys the ghost images while polarization entanglement encodes the imaging channels. Then whether imaging the single ghost image of a skull-shape object or not can be a direct yet intuitive signature to support or defy quantum mechanics. We use the contrast-to-noise ratio of ghost images to macroscopically characterize the degree of the violation of locality. We also showcase the nonlocal behavior of violating the locality with a reasonable confidence level of 75%, microscopically at the single-pixel level. Our strategy not only sheds new light on the fundamental issue of quantum mechanics, but also holds promise for developing hyper-entanglement-based quantum imaging technology.
Abstract Quantum‐correlation‐based ghost imaging, also termed quantum ghost imaging, has found applications as diverse as the fundamental tests of quantum mechanics and low‐light‐level imaging. In any previous schemes, however, only biphoton spatial entanglement is utilized, whereas other degrees of freedom of the photons have not yet been explored. Here we break this barrier to present a multichannel parallel ghost imaging system, by exploiting hyperentanglement where photon pairs are simultaneously entangled in polarization, color, and spatial mode. In the experiment, polarization and color entanglements provide 2× 2 independent channels via simultaneous polarization and color multiplexing, while an optical isolator with a delay line is constructed to ensure that spatial entanglement conveys the ghost image in parallel. The method can offer a pathway for high‐capacity quantum image processing and transmission in future quantum network.
Quantum ghost image technique utilizing position or momentum correlations between entangled photons can realize nonlocal reconstruction of the image of an object. In this work, based on polarization entanglement, we experimentally demonstrate quantum ghost imaging of vector images by using a geometric phase object. We also provide a corresponding theoretical analysis. Additionally, we offer a geometrical optics path explanation of ghost imaging for vector fields. The proposed strategy offers new insights into the fundamental development of ghost imaging and also holds great promise for developing complex structured ghost imaging techniques. Our work expanding the principle of ghost imaging to spatially varying vector beams will lead to interesting developments of this field.
Quantum Entanglement is widely regarded as one of the most prominent features of quantum mechanics and quantum information science. Although, photonic entanglement is routinely studied in many experiments nowadays, its signature has been out of the grasp for real-time imaging. Here we show that modern technology, namely triggered intensified charge coupled device (ICCD) cameras are fast and sensitive enough to image in real-time the effect of the measurement of one photon on its entangled partner. To quantitatively verify the non-classicality of the measurements we determine the detected photon number and error margin from the registered intensity image within a certain region. Additionally, the use of the ICCD camera allows us to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement, which suggests as well that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will improve applications of quantum science.
Quantum ghost imaging (GI) has significantly advanced the research and application of spatially entangled photon pairs over the past three decades. Nevertheless, existing works predominantly concentrate on qualitative analyses of GI results. The absence of rigorous theoretical models limits the capability of GI to address quantitative problems, which is essential in complex scenarios. Here, we present a comprehensive theoretical model that describes the evolution of the biphoton state throughout the GI process. Based on this model, we can explicitly analyze how the biphoton state evolves, and how object information is encoded into two-photon correlation measurements. We further introduce a virtual single-arm (VSA) operator, which maps the effects of two-arm optical elements into an equivalent single-arm representation, enabling a more intuitive analysis of biphoton-state evolution. Experimental validation is performed using a GI system based on an intensified charge-coupled device (ICCD) camera with multiple objects placed at different longitudinal positions. The excellent agreement between experimental and simulation results confirms the validity of the theoretical framework. This work clarifies the evolution of the biphoton states in quantum GI and opens new avenues for its applications in GI and broader quantum information tasks.
Bell nonlocality is both a defining signature of entanglement and a key quantum information resource. However, visualizing and certifying nonlocal correlations across a spatially multimode photonic field remains challenging due to the rapidly growing measurement cost of spatially resolved projective tests. To address this issue, we build a spatial nonlocality imaging scheme that directly reveals the spatial distribution of quantum nonlocality by integrating a metasurface that performs parallel polarization projections with a quantum-adaptive neural network. Spatially resolved Clauser--Horne--Shimony--Holt (CHSH) tests are realized over a 400-pixel biphoton field using an average of only 1.7 detected coincidence pairs per pixel per basis. This approach yields a nonlocality image that maps the two-dimensional spatial distribution of Bell violations across the optical field and reveals the target-state-dependent spatial evolution of Bell violations. It provides a highly resource-efficient route to large-scale Bell certification and opens new possibilities for exploiting spatially multimode entanglement in quantum imaging, quantum networking, and scalable photonic quantum technologies.