Extracting as much information as possible about an object when probing with a limited number of photons is an important goal with applications from biology and security to metrology. Imaging with a few photons is a challenging task as the detector noise and stray light are then predominant, which precludes the use of conventional imaging methods. Quantum correlations between photon pairs has been exploited in a so called 'heralded imaging scheme' to eliminate this problem. However these implementations have so-far been limited to intensity imaging and the crucial phase information is lost in these methods. In this work, we propose a novel quantum-correlation enabled Fourier Ptychography technique, to capture high-resolution amplitude and phase images with a few photons. This is enabled by the heralding of single photons combined with Fourier ptychographic reconstruction. We provide experimental validation and discuss the advantages of our technique that include the possibility of reaching a higher signal to noise ratio and non-scanning Fourier Ptychographic acquisition.
Extracting as much information as possible about an object when probing with a limited number of photons is an important goal with applications from biology and security to metrology. Imaging with a few photons is a challenging task as the detector noise and stray light are then predominant, which precludes the use of conventional imaging methods. Quantum correlations between photon pairs has been exploited in a so called 'heralded imaging scheme' to eliminate this problem. However these implementations have so-far been limited to intensity imaging and the crucial phase information is lost in these methods. In this work, we propose a novel quantum-correlation enabled Fourier Ptychography technique, to capture high-resolution amplitude and phase images with a few photons. This is enabled by the heralding of single photons combined with Fourier ptychographic reconstruction. We provide experimental validation and discuss the advantages of our technique that include the possibility of reaching a higher signal to noise ratio and non-scanning Fourier Ptychographic acquisition.
Imaging systems play a crucial role in shaping understanding of our surroundings. Modern imaging systems enable the acquisition of images of objects at length-scales and resolutions previously deemed impossible. However, as the drive for better images and novel applications increases, several questions fundamental to our understanding of imaging are being raised. We are familiar with images containing many millions of photons, but how many photons does it take to form an image? In scenarios requiring covert imaging, or where high-light levels damage the sample being imaged, is it possible to image a sample with a very small number of very low-energy photons? This thesis will focus on answering these two questions. In order to answer these questions I developed a heralded quantum imaging system. The strong spatial correlations inherent between down-converted twin photons have been utilised in many quantum imaging techniques for the past 25 years. Thus far, standard quantum imaging techniques have relied on scanning a fibre detector across the field of view in order to measure the spatial information in the image. However, the scanning mechanism fundamentally limits the detection efficiency of the imaging system. Recent years have seen an increased interest in using the latest camera technology within quantum imaging systems. The advent of single-photon-sensitive cameras has opened up new possibilities within the quantum imaging field. It is now possible to obtain images of objects by detecting very low-light illumination across the full scene simultaneously. In the heralded quantum imaging system presented in this thesis, a combination of quantum mechanics and a high-sensitivity camera was employed to obtain high contrast images containing very few photons. This was the first such system built. Using the correlations between the twin photons generated by our down-conversion source, and our development of compressive sampling techniques to post-process the acquired data enabled the acquisition of an image containing an average of only 0.5 photons per pixel. This represents a significant reduction when compared with a conventional image that contains of order 105 photons per pixel. I also developed this imaging system to use twin photons at vastly different wave- lengths. The object was probed with low-energy infrared photons whilst the image was developed on a camera using the correlated visible photon. This disparity in energy between the two photons enabled the acquisition of images using only several thousand photons, corresponding to an energy deposition on the sample of only a few pJ.
Quantum imaging with undetected light has recently emerged as a technique in which quantum correlations and nonlinear interferometry are combined to decouple illumination and detection paths. This approach has been more recently extended and combined with digital phase-shifting holography and off-axis holography to extract both the amplitude and phase information of a sample relying on single-photon interference. Despite these advantages, implementing the technique in real-world scenarios where the observed system is subject to environmental noise and dynamic variations remains challenging. The primary limitation lies in the inability of quantum imaging systems to retrieve object information in real time under high-noise conditions. Here, we experimentally demonstrate real-time amplitude and phase imaging in noisy environments, building upon our previous implementation of quantum off-axis holography. Our results demonstrate real-time imaging at acquisition rates up to 4~Hz, even when the noise level exceeds the signal by an order of magnitude.
Quantum imaging with undetected light (QIUL) can retrieve amplitude and phase information of an object by exploiting the quantum correlations of photon-pairs generated through spontaneous parametric down conversion (SPDC), where the illumination and detection can be carried at very distinct wavelength ranges. This fact allows to benefit from a mature detection technology in the visible spectral range, while probing the object at a more exotic wavelength. Here we experimentally implement a QIUL approach with Fourier off-axis holography in a hybrid-type induced-coherence non-linear interferometer. Our approach reconstructs the amplitude and phase information of an object with a single shot in a wide-field configuration, being an alternative in front of techniques that require multiple acquisition frames, such as phase-shifting holography.
Quantum correlations, especially time correlations, are crucial in ghost imaging for significantly reducing the background noise on the one hand while increasing the imaging resolution. Moreover, the time correlations serve as a critical reference, distinguishing between signal and noise, which in turn enable clear visualization of biological samples. Quantum imaging also addresses the challenge involved in imaging delicate biological structures with minimal photon exposure and sample damage. Here, we explore the recent progress in quantum correlation-based imaging, notably its impact on secure imaging and remote sensing protocols as well as on biological imaging. We also exploit the quantum characteristics of heralded single-photon sources (HSPS) combined with decoy state methods for secure imaging. This method uses Quantum Key Distribution (QKD) principles to reduce measurement uncertainties and protect data integrity. It is highly effective in low-photon number regimes for producing high-quality, noise-reduced images. The versatility of decoy state methods with WCSs (WCS) is also discussed, highlighting their suitability for scenarios requiring higher photon numbers. We emphasize the dual advantages of these techniques: improving image quality through noise reduction and enhancing data security with quantum encryption, suggesting significant potential for quantum imaging in various applications, from delicate biological imaging to secure quantum imaging and communication.
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.
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.