Systems of ultracold atoms in optical potentials have taken a place at the forefront of research into many-body atomic systems because of the clean experimental environment they exist in and the tunability of the system parameters. In this thesis we study how light scattered from these ultracold atomic gases reveals information about the state of the atomic gas and also leads to changes in that state. We begin by investigating the angular dependence of light scattered from atoms in optical lattices at finite temperature. We demonstrate how correlations in the superfluid and Mott insulator states affect the scattering pattern, and we show that temperature affects the number of photons scattered. This effect could be used to measure the temperature of the gas, however, we show that when the lattice band structure is taken into account the efficiency of this temperature measurement is reduced. We then investigate light scattering from small optical lattices where the Bose-Hubbard Hamiltonian can be solved exactly. For small lattices, scattering a photon from the atomic system significantly perturbs the atomic system. We develop a model of the evolution of the many-body state that results from the consecutive scattering and detection of photons. This model shows that light scattering pushes the system towards eigenstates of the light scattering measurement process, in some cases leading to a superposition of atomic states. In the second half of this thesis we study light scattering that depends on the internal hyperfine spin state of the atoms, in which case the scattered light can form images of the spatial atomic spin distribution. We demonstrate how scattering spatially correlated light from the atoms can result in spin state images with enhanced spatial resolution. We also show how using spatially correlated light can lead to direct measurement of the spatial correlations of the atomic spin distribution. We then apply this theory of spin-dependent light scattering to the detection of different spin states of ultracold gases in synthetic magnetic fields. We show that it is possible to distinguish between ground states in the quantum Hall regime using light scattering. Moreover, we show how noise correlation analysis of the spin state images can be used to identify the correlations between atoms and how a variant on phase-contrast imaging can reveal the relationship between the atomic spins.

Die einzigartige (bio)-chemische Spezifität der mittleren Infrarotmikroskopie birgt ein enormes Potential für eine breite Palette biomedizinischer und industrieller Anwendungen. Eine wesentliche Einschränkung ergibt sich jedoch durch die unzureichenden Detektionsmöglichkeiten in diesem Wellenlängenbereich, da derzeitige Mittelinfrarot-Detektoren meist durch geringere Leistungsfähigkeit bei deutlich höheren Anschaffungskosten gekennzeichnet sind. Dementsprechend verlagern neuentwickelte Technologien mitunter die Detektion in den sichtbaren Spektralbereich, in dem eine weitaus bessere, Silizium-basierte Kameratechnologie verfügbar ist. Ein solches Verfahren, das im Mittelpunkt dieser Arbeit steht, ist die Quantenbildgebung mit undetektiereten Photonen, welche sich zunehmend als leistungsfähiges Werkzeug für Infrarot-Bildgebung entwickelt. Der optische Aufbau basiert auf nichtlinearer Interferometrie bei der räumlich verschränkte, nicht-entartete Photonenpaare die Entkopplung der Analyse- und Detektionswellenlängen ermöglicht. Entsprechend wird die Bildgebung im mittleren Infrarotbereich durch die Detektion von Nahinfrarotlicht mit einer handelsüblichen CMOS-Kamera realisiert. In dieser Arbeit wird die beschriebene Methode auf die Mikroskopie übertragen, wodurch Abbildungen biologischer Gewebeproben im mittleren Infrarotbereich mit einer Auflösung von geringer als 10 Mikrometer angefertigt werden können. Darüber hinaus werden zwei Abbildungsregime untersucht, die auf den komplementären Impuls- und Positionskorrelationen der Photonenpaare basieren. Weiterführende Möglichkeiten der Kombination von Quanten-Bildgebung mit unentdeckten Photonen und FTIR-Spektroskopie zum Zwecke der räumlich-spektral kontinuierlichen Datenerfassung werden besprochen. Die vorgestellten Ergebnisse stellen die Entwicklungsfähigkeit der Quantenbildgebung mit unentdeckten Photonen unter Beweis und demonstrieren ihr Potential für praxisnahe Anwendungen in der Biomedizin und der Industrie. / The unique (bio)-chemical specificity of mid-infrared (IR) microscopy holds tremendous promise for a wide range of biomedical and industrial applications. Significant limitation, however, arises from poor detection capabilities in this wavelengths range, with current mid-IR detection technology often marrying inferior technical capabilities with prohibitive costs. Accordingly, emerging approaches shift detection into the visible regime, where vastly superior silicon-based camera technology is available. One such technique, and the one that is in the center of this thesis is quantum imaging with undetected photons (QIUP), which has recently emerged as a new powerful imaging tool. The optical layout is based on nonlinear interferometry, where spatially entangled non-degenerate photon pairs enable the decoupling of the sensing and detection wavelengths, facilitating mid-IR wide-field imaging through the detection of near-IR light with an off-the-shelf CMOS camera. Additionally, the method is expanded towards microscopy, attaining sub-10 μm resolution, demonstrating our technique is fit for purpose, acquiring microscopic images of biological tissue samples in the mid-IR. Additionally, two imaging regimes are explored, based on the complementary momentum and position correlations. A comparison between the two regimes is presented and some limitations of the technique are discussed. Further efforts of combining QIUP with Fourier Transform IR spectroscopy for spatio-spectral continuous data acquisition are reviewed. The presented results demonstrate the achieved progress towards advancing QIUP to enable real-world biomedical as well as industrial imaging applications.

Vision has always been one of the most important cognitive tools of human beings. In this regard, the development of image sensors opens up the potential to view objects that our eyes cannot see. One of the most promising capability in some image sensors is their single-photon sensitivity that provides information at the ultimate fundamental limit of light. Time-resolved single-photon avalanche diode (SPAD) image sensors bring a new dimension as they measure the arrival time of incident photons with a precision in the order of hundred picoseconds. In addition to this characteristic, they can be fabricated in complementary metal-oxide-semiconductor (CMOS) technology enabling the integration of complex signal processing blocks at the pixel level. These unique features made CMOS SPAD sensors a prime candidate for a broad spectrum of applications. This thesis is dedicated to the optimization and characterization of quantum imagers based on the SPADs as part of the E.U. funded SUPERTWIN project to surpass the fundamental diffraction limit known as the Rayleigh limit by exploiting the spatio-temporal correlation of entangled photons. The first characterized sensor is a 32×32-pixel SPAD array, named “SuperEllen”, with in-pixel time-to-digital converters (TDC) that measure the spatial cross-correlation functions of a flux of entangled photons. Each pixel features 19.48% fill-factor (FF) in 44.64-μm pitch fabricated in a 150-nm CMOS standard technology. The sensor is fully characterized in several electro-optical experiments, in order to be used in quantum imaging measurements. Moreover, the chip is calibrated in terms of coincidence detection achieving the minimal coincidence window determined by the SPAD jitter. The second developed sensor in the context of SUPERTWIN project is a 224×272-pixel SPAD-based array called “SuperAlice”, a multi-functional image sensor fabricated in a 110-nm CMOS image sensor technology. SuperAlice can operate in multiple modes (time-resolving or photon counting or binary imaging mode). Thanks to the digital intrinsic nature of SPAD imagers, they have an inherent capability to achieve a high frame rate. However, running at high frame rate means high I/O power consumption and thus inefficient handling of the generated data, as SPAD arrays are employed for low light applications in which data are very sparse over time and space. Here, we present three zero-suppression mechanisms to increase the frame rate without adversely affecting power consumption. A row-skipping mechanism that is implemented in both SuperEllen and SuperAlice detects the absence of SPAD activity in a row to increase the duty cycle. A current-based mechanism implemented in SuperEllen ignores reading out a full frame when the number of triggered pixels is less than a user-defined value. A different zero-suppression technique is developed in the SuperAlice chip that is based on jumping through the non-zero pixels within one row. The acquisition of TDC-based SPAD imagers can be speeded up further by storing and processing events inside the chip without the need to read out all data. An on-chip histogramming architecture based on analog counters is developed in a 150-nm CMOS standard technology. The test structure is a 16-bin histogram with 9 bit depth for each bin. SPAD technology demonstrates its capability in other applications such as automotive that demands high dynamic range (HDR) imaging. We proposed two methods based on processing photon arrival times to create HDR images. The proposed methods are validated experimentally with SuperEllen obtaining >130 dB dynamic range within 30 ms of integration time and can be further extended by using a timestamping mechanism with a higher resolution.

<p dir="ltr">Quantum-enhanced approaches enable high-resolution imaging and sensing with signal-to-noise ratios beyond classical limits. However, operating in the quantum regime is highly susceptible to environmental influences and experimental conditions. Implementing these techniques necessitates highly controlled environments or intricate preparation methods, which can restrict their practical applications. This thesis explores the practical applications of quantum sensing, focusing on thermal sensing with bright quantum sources in biological and electronic contexts. Additionally, I discuss the development of a multimode source for quantum imaging applications and an on-chip atomic interface for scalable light-atom interactions. I built all the experimental setups from the beginning; a microscope setup for nanodiamond-based thermal sensing inside living cells, a four-wave mixing setup using a Rb cell for thermal imaging of microelectronics and multimode source, and a vacuum chamber for on-chip atomic interface.</p><p dir="ltr">Quantum sensing can be realized using atomic spins or optical photons possessing quantum information. Among these, color centers inside diamonds stand out as robust quantum spin defects (effective atomic spins), maintaining their quantum properties even in ambient conditions. In this thesis, I studied the role of an ensemble of color centers inside nanodiamonds as a probe of temperature in a living cell. Our approach involves incubating nanodiamonds in endothelial culture cells to achieve sub-kelvin sensitivity in temperature measurement. The results reveal a temperature error of 0.38 K and a sensitivity of 3.46 K/sqrt(Hz)<i> </i>after 83 seconds of measurement. Furthermore, I discuss the constraints of nanodiamond temperature sensing in living cells, propose strategies to surmount these limitations, and explore potential applications arising from such measurements.</p><p dir="ltr">Another ubiquitous quantum probe is light with quantum properties. Photons, the particles of light, can carry quantum correlations and have minimal interactions with each other and, to some extent, the environment. This capability theoretically allows for quantum-enhanced imaging or sensing of sample’s properties. In this thesis, I report on the demonstration of quantum-enhanced temperature sensing in microelectronics using bright quantum optical signals. I discuss the first demonstration of quantum thermal imaging used to identify hot spots and analyze heat transport in electronic systems.</p><p dir="ltr">To achieve this, we employed lock-in detection of thermoreflectivity, enabling us to measure temperature changes in a micro-wire induced by an electric current with an accuracy better than 0.04 degrees, averaged over 0.1 seconds. Our results demonstrate a nearly 50 % improvement in accuracy compared to using classical light at the same power, marking the first demonstration of below-shot-noise thermoreflectivity sensing. We applied this imaging technique to both aluminum and niobium-based circuits, achieving a thermal resolution of 42 mK during imaging. We scanned a 48 × 48 μm<i> </i>area with 3-4 dB squeezing compared to classical measurements. Based on these results, we infer possibility of generating a 256×256 pixel image with a temperature sensitivity of 42 mK within 10 minutes. This quantum thermoreflective imaging technique offers a more accurate method for detecting electronic hot spots and assessing heat distribution, and it may provide insights into the fundamental properties of electronic materials and superconductors.</p><p dir="ltr">In transitioning from single-mode to multimode quantum imaging, I conducted further research on techniques aimed at generating multimode quantum light. This involved an in-depth analysis of the correlation characteristics essential for utilizing quantum light sources in imaging applications. To achieve the desired multimode correlation regime, I developed a system centered on warm Rubidium vapor with nonlinear gain and feedback processes. The dynamics of optical nonlinearity in the presence of gain and feedback can lead to complexity, even chaos, in certain scenarios. Instabilities in temporal, spectral, spatial, or polarization aspects of optical fields may arise from chaotic responses within an optical <i>x</i>(2) or <i>x</i>(3) nonlinear medium positioned between two cavity mirrors or preceding a single feedback mirror. However, the complex mode dynamics, high-order correlations, and transitions to instability in such systems remain insufficiently understood.</p><p dir="ltr">In this study, we focused on a <i>x</i>(3) medium featuring an amplified four-wave mixing process, investigating noise and correlations among multiple optical modes. While individual modes displayed intensity fluctuations, we observed a reduction in relative intensity noise approaching the standard quantum limit, constrained by the camera speed. Remarkably, we recorded a relative noise reduction exceeding 20 dB and detected fourth-order intensity correlations among four spatial modes. Moreover, this process demonstrated the capability to generate over 100 distinct correlated quadruple modes.</p><p dir="ltr">In addition to conducting multimode analysis to develop a scalable imaging system, I have explored methodologies aimed at miniaturizing light-atom interactions on a chip for the scalable generation of quantum correlations. While warm atomic vapors have been utilized for generating or storing quantum correlations, they are plagued by challenges such as inhomogeneous broadening and low coherence time. Enhancing control over the velocity, location, and density of atomic gases could significantly improve light-atom interaction. Although laser cooling is a common technique for cooling and trapping atoms in a vacuum, its implementation in large-scale systems poses substantial challenges. As an alternative, I focused on developing an on-chip system integrated with atomic vapor controlled by surface acoustic waves (SAWs).</p><p dir="ltr">Surface acoustic waves are induced by an RF signal along the surface of a piezoelectric material and have already been proven to be effective for manipulating particles within microfluidic channels. Expanding upon this concept, I investigated the feasibility of employing a similar approach to manipulate atoms near the surface of a photonic circuit. The interaction between SAWs and warm atomic vapor is expected as a mechanism for controlling atomic gases in proximity to photonic chips for quantum applications. Through theoretical analysis spanning molecular dynamics and fluid dynamics regimes, I identified the experimental conditions necessary to observe acoustic wave behavior in atomic vapor. To validate this theory, I constructed an experiment comprising a vacuum chamber housing Rb atoms and a lithium niobate chip featuring interdigital transducers for launching SAWs. However, preliminary experimental results yielded no significant signals from SAW-atom interactions. Subsequent analysis revealed that observing such interactions requires sensitivity and signal-to-noise ratio (SNR) beyond the capabilities of the current setup. Multiple modifications, including increasing buffer gas pressure and mitigating RF cross-talk, are essential for conclusively observing and controlling these interactions.</p>