Quantum resources can provide supersensitive performance in optical imaging. Detecting entangled photon pairs from spontaneous parametric down conversion (SPDC) with single-photon avalanche diode (SPAD) image sensor arrays (ISAs) enables practical wide-field quantum-enhanced imaging. However, matching the SPDC wavelength to the peak detection efficiency range of complementary metal-oxide-semiconductor (CMOS) compatible mass-producible SPAD-ISAs has remained technologically elusive, resulting in low imaging speeds to date. Here, we show that a recently developed visible-wavelength entangled photon source enables high-speed quantum imaging. By operating at high detection efficiency of a SPAD-ISA, we increase acquisition speed by more than an order of magnitude compared to previous similar quantum imaging demonstrations. Besides being fast, the quantum-enhanced phase imager operating at short wavelengths retrieves nanometer scale height differences, tested by imaging evaporated silica and protein microarray spots on glass samples, with sensitivity improved by a factor of 1.351 ± 0.004 over equivalent ideal classical imaging. This work represents an important stepping stone towards scalable real-world quantum imaging advantage, and may find use in biomedical and industrial applications as well as fundamental research.
Quantum resources can provide supersensitive performance in optical imaging. Detecting entangled photon pairs from spontaneous parametric down conversion (SPDC) with single-photon avalanche diode (SPAD) image sensor arrays (ISAs) enables practical wide-field quantum-enhanced imaging. However, matching the SPDC wavelength to the peak detection efficiency range of complementary metal-oxide-semiconductor (CMOS) compatible mass-producible SPAD-ISAs has remained technologically elusive, resulting in low imaging speeds to date. Here, we show that a recently developed visible-wavelength entangled photon source enables high-speed quantum imaging. By operating at high detection efficiency of a SPAD-ISA, we increase acquisition speed by more than an order of magnitude compared to previous similar quantum imaging demonstrations. Besides being fast, the quantum-enhanced phase imager operating at short wavelengths retrieves nanometer scale height differences, tested by imaging evaporated silica and protein microarray spots on glass samples, with sensitivity improved by a factor of 1.351 ± 0.004 over equivalent ideal classical imaging. This work represents an important stepping stone towards scalable real-world quantum imaging advantage, and may find use in biomedical and industrial applications as well as fundamental research.
(English) Entangled photon pairs can enhance optical imaging capabilities. Phase imaging allows detecting fine detail of transparent samples without potentially invasive fluorescent labelling, and here entanglement enables a higher signal-to-noise ratio (SNR) than possible with only classical light. Spatial correlations from spontaneous parametric down conversion (SPDC) photon pair sources can also be used to increase spatial resolution and robustness to noise and aberrations in imperfect optical systems. Quantum imaging therefore represents a powerful approach to push imaging science beyond its current limits. Until recently, the principal barrier to implementing useful quantum imaging schemes based on entangled photons has been technological, as scalable image sensors capable of multi-photon imaging were unavailable. However, this situation has changed with the development of single photon avalanche diode (SPAD) array cameras, as well as efficient high brightness entangled photon pair sources based on SPDC. These advances have led to the required components now approaching relative technological maturity, opening the window towards engineering useful and scalable systems that exploit entanglement in order to improve optical imaging. In this thesis, we show the development of a quantum imaging platform able to perform practical and fast spatially resolved multi-photon coincidence imaging with high SNR. Special focus is placed on wide-field entanglement-enhanced phase imaging capability, in order to extend experimental sensitivity beyond limits imposed by classical light. The main components of our platform are: sources of hyper-entangled photon pairs, a large field-of-view optical imaging system with phase measurement capabilities, and coincidence imaging using SPAD array cameras. More specifically, the thesis describes: •The first realization of a wide-field entanglement-enhanced phase imager. Wide-field here refers to the ability to acquire images across the entire field-of-view simultaneously (i.e. without need for pixel-to-pixel scanning, sometimes also called full-field). Quantum-enabled super-sensitivity in phase imaging beyond the capability of equivalent classical measurement is demonstrated by careful experimental noise and resource analysis methods. Our system’s capabilities were tested through several sample measurements corresponding to use cases with real-world relevance, including nanometre-scale feature step heights in transparent material, biomedical protein microarrays, as well as birefringent phase samples. •The development of general experimental and numerical tools to calculate photon pair coincidence images and videos from SPAD array cameras, with photon-counting and time-tagging readout modalities, as well as the retrieval of phase images resulting from multi-photon entanglement interference, by adapting techniques from interferometry and holography. We performed also a detailed study and optimization of the influence of different experimental parameters resulting image quality factors. •The evolution and optimization of our system towards real-time quantum imaging capability. Acquisition speed is a key element of usefulness, and in this thesis we integrate, first, a visible-wavelength entangled photon source, and second, a novel time-tagging SPAD array camera. The resulting entanglement-enabled imager presents an improvement by at least four orders of magnitude in measurement speed compared to previous state-of-the-art demonstrations, resulting in the ability to record ~Hz frame rate entangled photon pair coincidence videos. We show that this system, besides phase imaging, has additional applications in the form of real-time entangled state fidelity monitoring, and real-time point spread function characterization of optical systems, which has important applicability to adaptive optical imaging. (Español) Los pares de fotones entrelazados pueden mejorar la capacidad de obtención de imágenes. La formación de imágenes de fase permite detectar detalles de muestras transparentes con alta precisión y sin necesitar marcas fluorescentes potencialmente invasivas. Además, el entrelazamiento permite una mayor relación señal-ruido (SNR, por sus siglas en inglés) de la que es posible utilizando luz clásica. Las correlaciones espaciales de las fuentes de pares de fotones basadas en conversión paramétrica descendente espontánea (SPDC, por sus siglas en inglés) también pueden ser empleadas para aumentar la resolución espacial, y la robustez frente al ruido y a las aberraciones. Por tanto, las técnicas de captación de imagen cuántica son una potente estrategia para impulsar el campo de la ciencia de la fotografía especializada más allá de sus límites actuales. La mayor barrera en la implementación de esquemas de captación de imágenes cuánticas basadas en fotones entrelazados es principalmente tecnológica, al carecer de sensores de imagen escalables capaces de detectar imágenes multifotónicas. No obstante, el desarrollo de cámaras de matriz de fotodiodos de avalancha de fotón único (SPAD, por sus siglas en inglés), y de fuentes de pares de fotones entrelazados de alta eficiencia y brillo, basadas en SPDC, ha cambiado el panorama actual. Estos avances han permitido que los componentes necesarios alcancen una relativa madurez tecnológica, lo que abre una ventana de oportunidad para la ingeniería de sistemas útiles que aprovechan el entrelazamiento para mejorar la imagen óptica. En esta tesis, mostramos el desarrollo de una plataforma de captación de imágenes cuántica práctica y rápida, capaz de generar imágenes mediante el uso de coincidencias multifotónicas. Principalmente, nos centramos en la capacidad de formar imágenes de fase de campo amplio, mejoradas por entrelazamiento. Los componentes principales de nuestra plataforma son: fuentes de pares de fotones hiperentrelazados, un sistema óptico de imagen con un gran campo de visión y capacidad de medición de fase, y formación de imagen mediante la detección en coincidencias utilizando cámaras SPAD. Específicamente, la tesis describe: - La primera realización de un sistema de captación de imágenes de fase en configuración de campo amplio mejorado por entrelazamiento. Utilizando métodos de análisis del ruido y de los recursos, se logró demostrar la supersensibilidad en la medición de fase facilitada por iluminación con luz cuántica. Las capacidades de nuestro sistema se probaron con medidas correspondientes a ejemplos del mundo real, por ejemplo, midiendo microarreglos ultrafinos (grosor de nm) en materiales transparentes, muestras biomédicas de microarrays de proteínas, y de fase birrefringente. - El desarrollo de herramientas numéricas y experimentales generales para calcular imágenes y vídeos de coincidencias de pares de fotones con cámaras SPAD, con modos de lectura de conteo de fotones y etiquetado de tiempo. Además, se desarrolló la recuperación de imágenes de fase del entrelazamiento, adaptando técnicas de interferometría y holografía. Asimismo, se realizó un estudio detallado sobre la influencia de diferentes parámetros experimentales en los factores de calidad de imagen. La evolución y optimización de nuestro sistema hacia la formación de imágenes cuánticas en tiempo real. Se integró primero una fuente de fotones entrelazados de longitud de onda visible y, seguidamente, una nueva cámara SPAD con marcado temporal. El sistema resultante presenta una mejora de al menos cuatro órdenes de magnitud en la velocidad de medición en comparación con otras demostraciones. Esto confiere al sistema la capacidad de grabar vídeos de coincidencias de pares de fotones entrelazados con una tasa de fotogramas de Hz. Este sistema, además de medir la fase, tiene aplicaciones para monitorizar tanto la fidelidad de estados de entrelazamiento como la caracterización de la función de dispersión de punto.
Quantum technology promises improvements in imaging, computing, and communication, for example using the resource of entanglement between photons with spatial correlations. Detecting spatial correlations, or coincidences, between entangled photons scalably, efficiently, and affordably is therefore an essential capability. However, this task is non-trivial for existing camera technologies, which require low illumination intensities or low detection duty cycles to count coincidences at high signal-to-noise ratios, resulting in long acquisition time, or use expensive custom electronic components. Here, we present an entanglement imaging system based around a novel Single-Photon Avalanche Diode (SPAD) array camera, optimized for sparse illumination with correlated photon pairs. The system is capable of maintaining a duty cycle close to 100%, while simultaneously detecting spatially resolved coincidences with high SNR, enabling the acquisition of real-time entanglement videos at a ~Hz frame rate. We use our system to demonstrate real-time monitoring of entanglement interference visibility, optical system point spread function, as well as real-time widefield entanglement-enhanced phase imaging. Our results show that SPAD array cameras represent a natural choice for scalable entanglement detection and imaging applications.
Quantum techniques can be used to enhance the signal-to-noise ratio in optical imaging. Leveraging the latest advances in single-photon avalanche diode array cameras and multiphoton detection techniques, here, we introduce a supersensitive phase imager, which uses space-polarization hyperentanglement to operate over a large field of view without the need of scanning operation. We show quantum-enhanced imaging of birefringent and nonbirefringent phase samples over large areas, with sensitivity improvements over equivalent classical measurements carried out with equal number of photons. The potential applicability is demonstrated by imaging a biomedical protein microarray sample. Our technology is inherently scalable to high-resolution images and represents an essential step toward practical quantum-enhanced imaging.
Single-photon avalanche diode (SPAD) arrays are essential tools in biophotonics, optical ranging and sensing, and quantum optics. However, their small number of pixels, low quantum efficiency, and small fill factor have so far hindered their use for practical imaging applications. Here, we demonstrate full-field entangled photon-pair correlation imaging using a 100-kpixel SPAD camera. By measuring photon coincidences between more than 500 million pairs of positions, we retrieve the full point spread function of the imaging system and subsequently high-resolution images of target objects illuminated by spatially entangled photon pairs. We show that our imaging approach is robust against stray light, enabling quantum imaging technologies to move beyond laboratory experiments towards real-world applications such as quantum light detection and ranging.
By harnessing the properties of photonic quantum states and their interaction with the environment, quantum imaging promises to go beyond the limits of classical imaging. However, the inherent weakness of detected signals and the fragility of quantum states make their properties difficult to measure in practice. In recent years, the emergence of single-photon sensitive cameras enabled the field to take a step closer to practical applications. In this respect, singlephoton avalanche diode (SPAD) cameras are one the most promising technologies as they can detect single photons across many pixels with unparalleled speed, temporal resolution, and very low noise.
Spatial correlations between two photons are the key resource in realising many quantum imaging schemes. Measurement of the bi-photon correlation map is typically performed using single-point scanning detectors or single-photon cameras based on CCD technology. However, both approaches are limited in speed due to the slow scanning and the low frame-rate of CCD-based cameras, resulting in data acquisition times on the order of many hours. Here we employ a high frame rate, single photon avalanche diode (SPAD) camera, to measure the spatial joint probability distribution of a bi-photon state produced by spontaneous parametric down-conversion, with statistics taken over 107 frames acquired in just 140 seconds. We verified the presence of spatial entanglement between our photon pairs through the violation of an Einstein-Podolsky-Rosen criterion, with a confidence level of 227 sigmas. Our work demonstrates the potential of SPAD cameras in the rapid characterisation of photon correlations, leading the way towards quantum imaging in real-time.