We examine the resolution of a ghost imaging system for the case in which the entangled photons are nondegenerate in frequency. The signal photon illuminates the object and is detected by a bucket detector. The idler photon is detected by a point detector. We consider the two cases in which the imaging lens is in the same arm as the object and when it is in the other arm. In the first case, the Airy disk is shown to depend on the wavelength of the idler photon; however, because the magnification depends on the two wavelengths, the resolution of a pair of point scatters on the object depends on the wavelength of both photons. In cases in which the position of the object can be controlled, the minimum resolvable distance can be optimized. In the case in which the object is in the far field, the resolution depends only on the signal wavelength. In the second case, the Airy disk depends on the wavelength of both photons but the resolution depends on the signal photon. While the ghost imaging system has flexibility for certain applications, the resolution of the nondegenerate ghost imaging system does not offer improvement over the classical illumination of the object.
We examine the resolution of a ghost imaging system for the case in which the entangled photons are nondegenerate in frequency. The signal photon illuminates the object and is detected by a bucket detector. The idler photon is detected by a point detector. We consider the two cases in which the imaging lens is in the same arm as the object and when it is in the other arm. In the first case, the Airy disk is shown to depend on the wavelength of the idler photon; however, because the magnification depends on the two wavelengths, the resolution of a pair of point scatters on the object depends on the wavelength of both photons. In cases in which the position of the object can be controlled, the minimum resolvable distance can be optimized. In the case in which the object is in the far field, the resolution depends only on the signal wavelength. In the second case, the Airy disk depends on the wavelength of both photons but the resolution depends on the signal photon. While the ghost imaging system has flexibility for certain applications, the resolution of the nondegenerate ghost imaging system does not offer improvement over the classical illumination of the object.
In this paper we study the resolution of images illuminated by sources composed of N+1 photons in which one non-degenerate photon is entangled with N degenerate photons. The N degenerate photons illuminate an object and are collected by an N photon detector. The signal from the N photon detector is measured in coincidence with the non-degenerate photon giving rise to a ghost image. We discuss the case of three photons in various configurations and generalize to N+1. Using the Rayleigh criterion, we find that the system may give an improvement in resolution by a factor of N compared to using a classical source. For the case that the N-photon number detector is a point detector, a coherent image is obtained. If the N-photon detector is a bucket detector, the image is incoherent. The visibility of the image in both cases is 1. In the opposite case in which the non-degenerate photon is scattered by the object, then, using an N-photon point detector may reduce the Airy disk by a factor of N.
In this paper we study the resolution of images illuminated by sources composed of N+1 photons in which one non-degenerate photon is entangled with N degenerate photons. The N degenerate photons illuminate an object and are collected by an N photon detector. The signal from the N photon detector is measured in coincidence with the non-degenerate photon giving rise to a ghost image. We discuss the case of three photons in various configurations and generalize to N+1. Using the Rayleigh criterion, we find that the system may give an improvement in resolution by a factor of N compared to using a classical source. For the case that the N-photon number detector is a point detector, a coherent image is obtained. If the N-photon detector is a bucket detector, the image is incoherent. The visibility of the image in both cases is 1. In the opposite case in which the non-degenerate photon is scattered by the object, then, using an N-photon point detector may reduce the Airy disk by a factor of N.
We show that when the integration time of the single photon detectors is longer than the correlation time of the biphoton, the attainable spatial resolution in ghost imaging with entangled signal idler pairs generated in type II spontaneous parametric down conversion is limited by the angular spread of single-frequency-signal idler pairs. If, however, the detector integration time is shorter than the biphoton correlation time, the transverse k-vectors of different spectral components combine coherently in the image, improving the spatial resolution.
We show that, when the integration time of the single photon detectors is longer than the correlation time of the biphoton, the attainable spatial resolution in ghost imaging with entangled signal-idler pairs generated in type II spontaneous parametric down conversion is limited by the angular spread of single-frequency-signal-idler pairs. If, however, the detector integration time is shorter than the biphoton correlation time, the transverse k-vectors of different spectral components combine coherently in the image, improving the spatial resolution.
Pairs of entangled photos are used to reconstruct an image in the application area known as quantum ghost imaging. It is the correlation between the photon pair that allows for the reconstruction of the image, as opposed to single photon detection. The entangled photons are spatially separated into two independent paths, one to illuminate the object and the other which is collected by a spatially resolving detector. Initially, ghost imaging experiments accomplished spatially resolving detectors by moving a single-pixel detector throughout a transverse scanning area. Advancements consisted of using ultra-sensitive cameras to avoid a system consisting of physically moving detectors. Ultra-sensitive cameras are, however, expensive and have limited spectral sensitivity. Here we demonstrate an alternative by utilising a spatial light modulator and a bucket detector to spatially resolve what is detected. Importantly, the masks displayed on the spatial light modulator must constitute a complete basis to acquire a completely reconstructed image. Historically, imaging speeds have been slow and inefficient due to the quadratic increase in the scanning capability for spatially resolved detectors and the low light levels associated with quantum experiments. Here we additionally utilise machine and deep learning algorithms to improve both image reconstruction time and resolution. We demonstrate this with a non-degenerate ghost imaging setup where the physical parameters such as the mask type and resolution are varied and controlled on a spatial light modulator. Thereby answering the question: can we image an object without using a camera?
We present another step in our efforts to expand far-field imaging beyond the diffraction limit and beyond the limitations imposed by fluorescent labels. The model system we examine is based on the exploitation of entangled photon pairs at 810 nm generated by spontaneous parametric down conversion (SPDC) of a 405 nm source to resolve the separations of the line pairs of a series of two-dimensional objects. A ghost-imaging optical system directs signal and idler photons along two paths, one of which contains the objects. Images are constructed using a covariance analysis of the entangled pairs using typically 106 frames collected with an EMCCD detector that was calibrated to account for the number of entangled pairs of photons, which is necessary for an accurate determination of the resolution and its comparison with the classical method. Conservation of momentum requires that there is inversion symmetry between the transverse k vectors of the photons passing through the target and their entangled counterparts directed along the targetless path. Our covariance analysis not only addresses this symmetry but also that the width of the covariance peak is broader than a single pixel owing to the nature of SPDC and the details of the optical arrangement. Consideration of this broadening provides significant improvement of the image quality. The Heisenberg limit (HL) is achieved within experimental error: using the same optical alignment, the resolution obtained with entangled pairs of 810 nm photons is, within experimental error, twice that obtained with classical 810 nm photons. More importantly, the error bars of measurements with 810 nm entangled pairs are quantified by the Cramér-Rao lower bound (CRLB) and compared with those of the classical measurements. While other workers have done quantum imaging on nonpoint sources, to our knowledge we are the first group that not only has done the quantum imaging but also has compared the CRLB and the measured error of the quantum and classical measurements for a series of different-sized objects. (Similar comparisons have, however, been made for systems that can be approximated as point sources, e.g., determining the separation of two laser beams).