Quantum Ghost Research Articles

Fast quantum ghost imaging with a single-photon-sensitive time-stamping camera.

Quantum ghost imaging (QGI) leverages correlations between entangled photon pairs to reconstruct an image using light that has never physically interacted with an object. Despite extensive research interest, this technique has long been hindered by slow acquisition speeds, due to the use of raster-scanned detectors or the slow response of intensified cameras. Here, we utilize a single-photon-sensitive time-stamping camera to perform QGI at ultra-low-light levels with rapid data acquisition and processing times, achieving high-resolution and high-contrast images in under 1 min. Our work addresses the trade-off between image quality, optical power, data acquisition time, and data processing time in QGI, paving the way for practical applications in biomedical and quantum-secured imaging.

Translated object identification for efficient ghost imaging.

Alignment of a single-pixel quantum ghost imaging setup is complex and requires extreme precision. Due to misalignment, easily created by human error in the alignment process, reconstructed images are often translated off the central imaging axis. This becomes problematic for intelligent object detection and identification in fast imaging cases, as these algorithms are unable to achieve early image identification. Here, we implemented a U-net algorithm to correctly recognize images in the early reconstruction stage regardless of any off-axis translation. The U-net was trained on a uniquely curated blurred, noised, and off-axis translated dataset. We achieved a 5× reduction in imaging speeds by early image identification in four different translation directions.

Quantum ghost imaging microscopy depth-of-field study

Quantum ghost imaging approaches have been proposed to enhance biological microscopy, for example, using 2D visible detectors to provide IR images or providing additional dimensions of spatial or spectral information. Toward the goal of making such imaging schemes practical, we compare image quality and depth-of-field between traditional images and ghost images at the same excitation levels. We measure how image quality and depth-of-field depend on the parameters of the entangled light produced using type-I spontaneous parametric down-conversion (SPDC). We use a pair of time-synchronized, photon-timing single-photon avalanche diode (SPAD) array detectors to capture two distinct microscope imaging paths simultaneously on a photon-pair-by-photon-pair basis: one in a traditional imaging pathway and the other a quantum ghost imaging pathway. We calculate the depth-of-field, resolution, contrast, and signal-to-noise ratio (SNR) through the parameter space of a β-Barium Borate (BBO) type-I bulk non-linear crystal length and angle. Our results provide a basis for choosing parameters for quantum ghost imaging with type-I SPDC sources.

Infrared quantum ghost imaging of living and undisturbed plants

Infrared quantum ghost imaging of living and undisturbed plants

A Method to Correct the Temporal Drift of Single-Photon Detectors Based on Asynchronous Quantum Ghost Imaging.

Single-photon detection and timing has attracted increasing interest in recent years due to their necessity in the field of quantum sensing and the advantages of single-quanta detection in the field of low-level light imaging. While simple bucket detectors are mature enough for commercial applications, more complex imaging detectors are still a field of research comprising mostly prototype-level detectors. A major problem in these detectors is the implementation of in-pixel timing circuitry, especially for two-dimensional imagers. One of the most promising approaches is the use of voltage-controlled ring resonators in every pixel. Each of these runs independently based on a voltage supplied by a global reference. However, this yields the problem that the supply voltage can change across the chip which, in turn, changes the period of the ring resonator. Due to additional parasitic effects, this problem can worsen with increasing measurement time, leading to drift in the timing information. We present here a method to identify and correct such temporal drifts in single-photon detectors based on asynchronous quantum ghost imaging. We also show the effect of this correction on recent quantum ghost imaging (QGI) measurement from our group.

Advances in Quantum Imaging with Machine Intelligence

AbstractQuantum imaging exemplifies the fascinating and counter‐intuitive nature of the quantum world, where non‐local correlations are exploited for imaging of objects by remote and non‐interacting photons. The field has exploded of late, driven by advances in our fundamental understanding of these processes, but also by advances in technology, for instance, efficient single photon detectors and cameras. Accelerating the progress is the nascent intersection of quantum imaging with artificial intelligence and machine learning, promising enhanced speed and quality of quantum images. This review provides a comprehensive overview of the rapidly evolving field of quantum imaging with a specific focus on the intersection of quantum ghost imaging with artificial intelligence and machine learning techniques. The seminal advances made to date and the open challenges are highlighted, and the likely trajectory for the future is outlined.

Quantum ghost imaging of a vector field.

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.

All-digital quantum ghost imaging: tutorial

Quantum ghost imaging offers many advantages over classical imaging, including the ability to probe an object with one wavelength and record the image with another, while low photon fluxes offer the ability to probe objects with fewer photons, thereby avoiding photo-damage to light sensitive structures such as biological organisms. Progressively, ghost imaging has advanced from single-pixel scanning systems to two-dimensional (2D) digital projective masks, which offer a reduction in image reconstruction times through shorter integration times. In this tutorial, we describe the essential ingredients in an all-digital quantum ghost imaging experiment and guide the user on important considerations and choices to make, aided by practical examples of implementation. We showcase several image reconstruction algorithms using two different 2D projective mask types and discuss the utility of each. We additionally discuss a notable artifact of a specific reconstruction algorithm and projective mask combination and detail how this artifact can be used to retrieve an image signal heavily buried under artifacts. Finally, we end with a brief discussion on artificial intelligence (AI) and machine learning techniques used to reduce image reconstruction times. We believe that this tutorial will be a useful guide to those wishing to enter the field, as well as those already in the field who wish to introduce AI and machine learning to their toolbox.

3D quantum ghost imaging.

We present current results of a novel, to the best of our knowledge, type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors, first presented in [Appl. Opt.60, F66 (2021)APOPAI0003-693510.1364/AO.423634]. The scheme enables photon pairing without fixed delays and, thus, overcomes some limitations of the widely used heralded setups for quantum ghost imaging [Nat. Commun.6, 5913 (2015)NCAOBW2041-172310.1038/ncomms6913]. It especially allows three-dimensional (3D) imaging by direct time of flight methods, the first demonstration of which will be shown here. To our knowledge, it is also the first demonstration of 3D quantum ghost imaging at all.

Quantum ghost imaging based on a "looking back" 2D SPAD array.

Quantum ghost imaging (QGI) is an intriguing imaging protocol that exploits photon-pair correlations stemming from spontaneous parametric down-conversion (SPDC). QGI retrieves images from two-path joint measurements, where single-path detection does not allow us to reconstruct the target image. Here we report on a QGI implementation exploiting a two-dimensional (2D) single-photon avalanche diode (SPAD) array detector for the spatially resolving path. Moreover, the employment of non-degenerate SPDC allows us to investigate samples at infrared wavelengths without the need for short-wave infrared (SWIR) cameras, while the spatial detection can be still performed in the visible region, where the more advanced silicon-based technology can be exploited. Our findings advance QGI schemes towards practical applications.

Patterns for all-digital quantum ghost imaging generated by the Ising model

We present new illumination patterns for imaging in all-digital quantum ghost imaging (GI) systems. The digital patterns, written as computer generated holograms on spatial light modulators (SLM), are generated by the Ising model, a well-known ferromagnetic model. In general, Ising patterns are affected by two parameters: temperature (T) and magnetic field (H). Here, we set H to 0 and offer a method for applying Ising patterns made with various T values to reconstruct high quality ghost images with very little background noise.

Revealing the embedded phase in single-pixel quantum ghost imaging

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.

Front Cover: Time‐Efficient Object Recognition in Quantum Ghost Imaging (Adv. Quantum Technol. 2/2023)

The cover illustrates the birth of entangled photons used in quantum ghost imaging. The idler photons interact with the object while the signal photons are spatially resolved. Machine learning (ML) is employed to speed up the quantum imaging process. The nodal sphere is representative of ML while the 0 s and 1 s represent early recognition by logistic regression. Logistic regression demonstrates a 10x speed up in image acquisition time with a 99% prediction accuracy. More details can be found in article number 2200109 by Chané Moodley and co-workers.

Quantum-enabled ghost imaging for non-invasive imaging of plants.

Imaging biological processes in plants, such as water transport and sequestration, without disturbing natural growth or introducing artificial stimuli is challenging. Most optical microscopy techniques involve fluorescent probes and/or high-intensity light to obtain structural and chemical signatures. Spatially resolved near-infrared (NIR) absorption, for example, captures information about chemical signatures, but is typically obtained with time-intensive scanned confocal techniques because there are few spatially-resolvable detectors (cameras) in the NIR. Furthermore, confocal microscopy illuminates living samples with significant light intensities that can damage or alter the organism. To image chemical signatures, such as water, in undisturbed plants, we developed a quantum ghost imaging microscope that leverages non-degenerate spontaneous parametric down conversion (SPDC). Samples are probed with low levels of NIR light. Due to quantum correlation with their visible SPDC photon pairs, an image of the NIR absorption can be obtained using a spatially-resolving detector in the visible. We describe the operating principle and first measurements of this new imaging technique.

Snapshot hyperspectral imaging with quantum correlated photons.

Hyperspectral imaging (HSI) has a wide range of applications from environmental monitoring to biotechnology. Conventional snapshot HSI techniques generally require a trade-off between spatial and spectral resolution and are thus limited in their ability to achieve high resolutions in both simultaneously. Most techniques are also resource inefficient with most of the photons lost through spectral filtering. Here, we demonstrate a proof-of-principle snapshot HSI technique utilizing the strong spectro-temporal correlations inherent in entangled photons using a modified quantum ghost spectroscopy system, where the target is directly imaged with one photon and the spectral information gained through ghost spectroscopy from the partner photon. As only a few rows of pixels near the edge of the camera are used for the spectrometer, effectively no spatial resolution is sacrificed for spectral. Also since no spectral filtering is required, all photons contribute to the HSI process making the technique much more resource efficient.

Time‐Efficient Object Recognition in Quantum Ghost Imaging

AbstractAcquiring information at the fastest possible rate is often desirable, particularly in quantum ghost imaging which suffers from slow reconstruction speeds. Many computationally intense deep‐learning methods have been implemented in an effort to speed up image acquisition times by retrieving image information. Often over‐looked, machine learning methods can offer the same, if not better, speed up in image acquisition time by an object recognition process. Four machine learning algorithms are implemented and trained on a uniquely generated, noised, and blurred dataset of numerical digits 1 through 9. Of the tested recognition algorithms, logistic regression shows a 10× speed up in image acquisition time with a 99% prediction accuracy. Additionally, this reduction in acquisition time is achieved without any image denoising or enhancement prior to recognition, thereby reducing training and implementation time, as well as the computational intensity of the approach. This method can be implemented in real‐time, requiring only 1/10th of the measurements needed for a general solution, making it ideal for quantum imaging and recognition of light sensitive structure.

Background effective action with nonlinear massive gauge fixing

We combine a recent construction of a Becchi-Rouet-Stora-Tyutin (BRST)-invariant, nonlinear massive gauge fixing with the background field formalism. The resulting generating functional preserves background-field invariance as well as BRST invariance of the quantum field manifestly. The construction features BRST-invariant mass parameters for the quantum gauge and ghost fields. The formalism employs a background Nakanishi-Lautrup field which is part of the nonlinear gauge-fixing sector and thus should not affect observables. We verify this expectation by computing the one-loop effective action and the beta function of the gauge coupling as an example. The corresponding Schwinger functional generating connected correlation functions acquires additional one-particle reducible terms that vanish on shell. We also study off-shell one-loop contributions in order to explore the consequences of a nonlinear gauge fixing scheme involving a background Nakanishi-Lautrup field. As an application, we show that our formalism straightforwardly accommodates nonperturbative information about propagators in the Landau gauge in the form of the so-called decoupling solution. Using this nonperturbative input, we find evidence for the formation of a gluon condensate for sufficiently large coupling, whose scale is set by the BRST-invariant gluon mass parameter.

Quantum ghost imaging of a transparent polarisation sensitive phase pattern

A transparent polarisation sensitive phase pattern exhibits a position and polarisation dependent phase shift of transmitted light and it represents a unitary transformation. A quantum ghost image of this pattern is produced with hyper-entangled photons consisting of Einstein-Podolsky-Rosen (EPR) and polarisation entanglement. In quantum ghost imaging, a single photon interacts with the pattern and is detected by a stationary detector and a non-interacting photon is imaged on a coincidence camera. EPR entanglement manifests spatial correlations between an object plane and a ghost image plane, whereas a polarisation dependent phase shift exhibited by the pattern is detected with polarisation entanglement. In this quantum ghost imaging, the which-position-polarisation information of a photon interacting with the pattern is not present in the experiment. A quantum ghost image is constructed by measuring correlations of the polarisation-momentum of an interacting photon with polarisation-position of a non-interacting photon. The experiment is performed with a coincidence single photon detection camera, where a non-interacting photon travels a long optical path length of 17.83 m from source to camera and a pattern is positioned at an optical distance of 19.16 m from the camera.

Some Features of the Formation of Quantum Ghost Imaging Considering the Effects of Self-Phase Modulation, Cross-Phase Modulation, and Phase-Mismatch

Some Features of the Formation of Quantum Ghost Imaging Considering the Effects of Self-Phase Modulation, Cross-Phase Modulation, and Phase-Mismatch

Effect of Multiple Positions Illumination in Quantum Ghost Imaging

Effect of Multiple Positions Illumination in Quantum Ghost Imaging