We propose a quantum diffraction imaging technique whereby one photon of an entangled pair is diffracted off a sample and detected in coincidence with its twin. The image is obtained by scanning the photon that did not interact with matter. We show that when a dynamical quantum system interacts with an external field, the phase information is imprinted in the state of the field in a detectable way. The contribution to the signal from photons that interact with the sample scales as [Formula: see text], where [Formula: see text] is the source intensity, compared with [Formula: see text] of classical diffraction. This makes imaging with weak fields possible, providing high signal-to-noise ratio, avoiding damage to delicate samples. A Schmidt decomposition of the state of the field can be used for image enhancement by reweighting the Schmidt modes contributions.
We propose a quantum diffraction imaging technique whereby one photon of an entangled pair is diffracted off a sample and detected in coincidence with its twin. The image is obtained by scanning the photon that did not interact with matter. We show that when a dynamical quantum system interacts with an external field, the phase information is imprinted in the state of the field in a detectable way. The contribution to the signal from photons that interact with the sample scales as [Formula: see text], where [Formula: see text] is the source intensity, compared with [Formula: see text] of classical diffraction. This makes imaging with weak fields possible, providing high signal-to-noise ratio, avoiding damage to delicate samples. A Schmidt decomposition of the state of the field can be used for image enhancement by reweighting the Schmidt modes contributions.
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.
Quantum correlation, such as entanglement and squeezing have shown to improve phase estimation in interferometric setups on one side, and non-interferometric imaging scheme of amplitude object on the other. In the last case, quantum correlation among a pair of beams leads to a sub-shot-noise readout of the image intensity pattern, where weak details, otherwise hidden in the noise, can be appreciated. In this paper we propose a technique which exploits entanglement to enhance quantitative phase retrieval of an object in a non-interferometric setting, i.e only measuring the propagated intensity pattern after interaction with the object. The method exploits existing technology, it operates in wide field mode, so does not require time consuming raster scanning and can operate with small spatial coherence of the incident field. This protocol can find application in optical microscopy and X-ray imaging, reducing the photon dose necessary to achieve a fixed signal-to-noise ratio.
Entangled photons can be exploited for single-photon imaging: photons are accumulated one by one to form an image on a camera. To improve the signal-to-noise ratio, one can use “heralded imaging,” where camera data is only accepted if a partner (entangled) photon is detected in coincidence, at a second detector. A secondary consequence of the strong correlations between entangled photons is that we can place the object into the path of the second detector, and yet still create an image on the original camera, using only photons that never interacted with the viewed object. This configuration is called “ghost imaging.” To reduce cost, we designed and implemented a modified version, replacing the fast-gated camera with single-photon sensitivity with a single-pixel detector that scans the image plane. Our design had to carefully preserve optical alignment so that the detector is always pointing at the source of entangled photons. Our next step will be to use ghost diffraction to demonstrate that entangled phone pairs are correlated in ways that extend beyond what is allowed by classical physics.
Biphoton phase imaging via two-photon coincidence detection is essential for quantum holography and related quantum imaging applications. Although camera-based methods have been predominantly used in previous studies, we here introduce a two-dimensional scanning method for biphoton phase imaging in quantum holography, which leverages a high-efficiency single-photon detector, improving signal-to-noise ratio (SNR). Using this platform, we obtained a quantum holographic phase image with an SNR above 19 and experimentally verified the noise-resilient nature of quantum holography under scanning-based detection. By using the brighter quantum sources, our method offers an efficient route toward faster two-photon coincidence imaging, which is expected to facilitate broader applications of quantum imaging in noisy environments.
Two-photon states generated through degenerate spontaneous parametric downconversion (SPDC) can exhibit sharp correlations in the transverse spatial coordinates. This property leads to unique free-space propagation features. Here, we show that a phase object placed in the image plane of the source affects the free space propagation of the SPDC in a way that is mathematically analogous to the Fresnel diffraction of a first-order coherent source. This effect can be observed via the extraction of correlation images. We demonstrate this prediction with an experiment where the diffraction of correlated bi-photons is detected using an event-based camera. The results allow us to reconstruct the phase structure of the sample via non-interferometric phase retrieval methods. We verify that the retrieved phase patterns exhibit a factor of two contrast enhancement due to the probe’s two-photon nature. Our findings offer a proof of principle application for quantitative phase imaging, particularly in regimes where low light conditions are required to prevent photo-damage and, at the same time, is desirable to preserve high resolution, contrast, and low noise.
Laser confocal imaging technology has become an important analytical tool in biological, biomedical, and materials science research, offering high imaging precision. However, this technology still has some limitations, especially in imaging biological samples (such as living tissues or cells), where the high intensity of the laser may cause irreversible photodamage. It has been proposed that quantum entangled light sources, instead of laser, can be used to avoid this drawback. In this paper, we experimentally demonstrated a quantum confocal imaging technology employing entangled photon sources with high brightness and stability. In the experiment, we obtained the point-by-point scanning imaging of a targeted area, in which a resolution of 3.91 µm is achieved and the signal-to-noise ratio (SNR) degradation is suppressed. We also theoretically analyzed the potential of quantum confocal imaging to improve SNR performance in photodamage-free imaging. Our results could widen the application fields of confocal imaging technology and pave the way for applying the quantum technology in biological imaging.