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Optica

Revealing the embedded phase in single-pixel quantum ghost imaging

Bereneice Sephton, Isaac M. Nape, Chané Moodley, Jason Francis, Andrew Forbes

Published Jan 17, 2023• 30 citations
Publisher

Abstract

Single-pixel quantum ghost imaging involves the exploitation of non-local photon spatial correlations to image objects with light that has not interacted with them and, using intelligent spatial scanning with projective masks, reduces detection to a single pixel. Despite many applications, extension to complex amplitude objects remains challenging. Here, we reveal that the necessary interference for phase retrieval is naturally embedded in the correlation measurements formed from traditional projective masks in bi-photon quantum ghost imaging. Using this, we develop a simple approach to obtain the full phase and amplitude information of complex objects. We demonstrate straightforward reconstruction without ambiguity using objects exhibiting spatially varying structures from phase steps to gradients as well as complex amplitudes. This technique could be an important step toward imaging the phase of light-sensitive structures in biological matter.

DOI
10.1364/optica.472980

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Single-pixel quantum ghost imaging involves the exploitation of non-local photon spatial correlations to image objects with light that has not interacted with them and, using intelligent spatial scanning with projective masks, reduces detection to a single pixel. Despite many applications, extension to complex amplitude objects remains challenging. Here, we reveal that the necessary interference for phase retrieval is naturally embedded in the correlation measurements formed from traditional projective masks in bi-photon quantum ghost imaging. Using this, we develop a simple approach to obtain the full phase and amplitude information of complex objects. We demonstrate straightforward reconstruction without ambiguity using objects exhibiting spatially varying structures from phase steps to gradients as well as complex amplitudes. This technique could be an important step toward imaging the phase of light-sensitive structures in biological matter.
We outline and experimentally demonstrate a method to image pure phase objects using traditional quantum ghost imaging with single pixel detectors. We provide a theoretical description of the process, showing how phase information is embedded in the correlation measurements of spatially entangled photon pairs in which only one of the pair interacts with the object. Using pairs of digital projective masks, one amplitude-only and one phase-only, we reconstruct two partial phase images of the object. Using both these images, we can retrieve the full detailed phase profile of the object without ambiguity, which we demonstrate on objects exhibiting phase steps and gradients.
Quantum ghost imaging harnesses entangled photon pairs to form images using light that never directly interacts with the object. Conventional approaches rely on pixelated detectors or spatial masks, where the resolution is fundamentally limited by the pixel size and thus bounded by the Rayleigh criterion. In this work, we present a modal approach that replaces pixel-based detection with measurements in a basis of structured modes. By reconstructing images through tailored spatial modes, we decouple resolution from the physical limitations of detectors and instead tie it to the system’s optical precision and computational control. We demonstrate that even non-orthogonal modal sets can achieve high fidelity image reconstruction by exploiting modal sparsity, significantly reducing the number of required measurements. Using phase-only approximations of Hermite-Gaussian modes, we avoid the loss associated with complex amplitude modulation while retaining high reconstruction fidelity. The result is a high-resolution, high-efficiency quantum ghost imaging technique powered by structured light, opening new possibilities for photon-efficient imaging in low-light and quantum-limited regimes, such as biological microscopy and remote sensing.
Correlated light (either classical or quantum) can be employed in various ways to improve resolution and measurement sensitivity. In an “interaction-free” measurement, a single photon can be used to reveal the presence of an object placed within one arm of an interferometer without being absorbed by it. This method has previously been applied to imaging. With a technique known as “ghost imaging”, entangled photon pairs are used for detecting an opaque object with significantly improved signal-to-noise ratio while preventing over-illumination. Here, we integrate these two methods to obtain a new imaging technique which we term “interaction-free ghost-imaging” that possesses the benefits of both techniques. While improving the image quality of conventional ghost-imaging, this new technique is also sensitive to phase and polarization changes in the photons introduced by a structured object. Furthermore, thanks to the “interaction-free” nature of this new technique, it is possible to reduce the number of photons required to produce a clear image of the object (which could be otherwise damaged by the photons) making this technique superior for probing light-sensitive materials and eventually biological tissues. If time allows, I will discuss some follow-up works involving partial measurements and remote erasure/completion of images. The latter techniques can help to suppress various types of noise during the imaging process.
Correlated-photon imaging, popularly known as ghost imaging, is a technique whereby an image is formed from light that has never interacted with the object. In ghost imaging experiments two correlated light fields are produced. One of these fields illuminates the object, and the other field is measured by a spatially resolving detector. In the quantum regime, these correlated light fields are produced by entangled photons created by spontaneous parametric down-conversion. To date, all correlated-photon ghost-imaging experiments have scanned a single-pixel detector through the field of view to obtain the spatial information. However, scanning leads to a poor sampling efficiency, which scales inversely with the number of pixels, N, in the image. In this work we overcome this limitation by using a time-gated camera to record the single-photon events across the full scene. We obtain high-contrast images, 90%, in either the image plane or the far-field of the photon pair source, taking advantage of the EPR-like correlations in position and momentum of the photon pairs. Our images contain a large number of modes, >500, creating opportunities in low-light-level imaging and in quantum information processing.
Abstract In a conventional quantum imaging experiment, the image of the object is retrieved directly with single photon camera technology, or computationally with a single‐pixel detector and pixelated projective masks. In all these approaches, the resolution of the image is dictated by the pixel resolution of the detection devices. In this paper, the traditional spatial basis of pixels is replaced with spatial modes, exploiting their unique features to enhance image fidelity and resolution and improve reconstruction accuracy through modal sparsity. This approach can be used even when the modes are not orthogonal, demonstrating the principle with highly efficient phase‐only approximations to the modal basis. By numerical simulation and experimental analysis, the advantages of this approach are illustrated, which include faster convergence to the object, with higher signals and fidelity, which are demonstrated with an order of magnitude less masks than conventional approaches for the same fidelity in outcome. Unlike the basis of pixels, the resolution of the image is not dictated by the resolution of the detectors, opening a path to high‐resolution quantum imaging of complex objects.