Photonic quantum sensing is attracting attention since it outperforms photonic sensing with classical light. Here we present photonic quantum sensing that harnesses the quantum properties of not only light source but also measurement system. First, we introduce nonlinear interferometer as an approach to introduce quantum properties to measurement system, and then show our proposal and the theoretical results of a loss tolerant quantum absorption measurement. We also show photonic quantum sensing, which enables us to detect ultra-faint signal light at a photon counting level under huge noisy environments. We also discuss the future directions and challenges of photonic quantum sensing using the quantum properties of measurement system, including applications to microscopy and spectroscopy.
Photonic quantum sensing is attracting attention since it outperforms photonic sensing with classical light. Here we present photonic quantum sensing that harnesses the quantum properties of not only light source but also measurement system. First, we introduce nonlinear interferometer as an approach to introduce quantum properties to measurement system, and then show our proposal and the theoretical results of a loss tolerant quantum absorption measurement. We also show photonic quantum sensing, which enables us to detect ultra-faint signal light at a photon counting level under huge noisy environments. We also discuss the future directions and challenges of photonic quantum sensing using the quantum properties of measurement system, including applications to microscopy and spectroscopy.
Quantum sensing using photons has attracted attention in recent years. In this talk, we report our two recent works on photonic quantum technologies for quantum sensing. First, we report a loss-tolerant quantum absorption measurement using quantum destructive interference in a nonlinear interferometer. Our theoretical results show that our approach surpasses the conventional quantum scheme under photon loss at the detection stage. Second, we report an adaptive quantum state estimation (AQSE) with which we can estimate an unknown quantum state with the smallest uncertainty. We show our experimental demonstrations of AQSE using photons, including a recently realized novel protocol for quantum states changing in time.
The application of quantum states of light such as entangled photons, for example, created by parametric down conversion, has experienced tremendous progress in the almost 40 years since their first experimental realization. Initially, they were employed in the investigation of the foundations of quantum physics, such as the violation of Bell's inequalities and studies of quantum entanglement. They later emerged as basic platforms for quantum communication protocols and, in the recent experiments on single-photon interactions, in photonic quantum computation. These applications aim at the controlled manipulation of the photonic degrees of freedom, and therefore rely on simple models of matter, where the analysis is simpler. Furthermore, quantum imaging with entangled light can achieve enhanced resolution, and quantum metrology can overcome the shot noise limit for classical light. This Account focuses on an entirely different emerging class of applications using quantum light as a powerful spectroscopic tool to reveal novel information about complex molecules. These applications utilize two appealing properties of quantum light: its distinct intensity fluctuations and its nonclassical bandwidth properties. These give rise to new and surprising behavior of nonlinear optical signals. Nonclassical intensity fluctuations can enhance nonlinear optical signals relative to linear absorption. For instance, the two-photon absorption of entangled photon pairs scales linearly (rather than quadratically) in the photon flux, just like a single photon absorption. This enables nonlinear quantum spectroscopy of photosensitive, for example, biological, samples at low light intensities. We will discuss how the two-photon absorption cross section becomes a function of the photonic quantum state, which can be manipulated by properties of the entangled photon pairs. In addition, the quantum correlations in entangled photon states further influence the nonlinear signals in a variety of ways. Apart from affecting the signal's scaling with intensity, they also constitute an entirely new approach to shaping and controlling excitation pathways in molecular aggregates in a way that cannot be achieved with shaped classical pulses. This is because between the two absorption events in entangled two-photon absorption, the light and material system are entangled. Classical constraints for the simultaneous time and frequency resolution can thus be circumvented, since the two are not Fourier conjugates. Here we review the simplest manifestation of quantum light spectroscopy, two-photon absorption spectroscopy with entangled photons. This will allow us to discuss exemplarily the impact of quantum properties of light on a nonlinear optical signal and explore the opportunities for future applications.
While the fundamental principles of light-matter interaction are well-understood and drive countless technologies, the world of multiphoton processes remains a fascinating puzzle, holding the potential to drastically alter our understanding of how light interacts with matter at its most basic level. This rich interplay of light and matter unveils novel phenomena that can be harnessed for sensing with exceptional precision, as exemplified by multiphoton quantum sensing. This thesis delves into the applications of multiphoton quantum protocols, particularly in imaging, communication, and plasmonic sensing, to surpass classical limitations and achieve enhanced sensitivity. We explore the potential of multiphoton quantum processes, particularly in the nanoscale regime and within subsystems of macroscopic systems, where novel and ultra-sensitive sensing methodologies emerge. Subsequent chapters of this thesis demonstrate the transformative potential of multiphoton quantum sensing, elucidating the design, implementation, and experimental results of specific sensing protocols tailored to diverse applications. Our analysis combines experimental observations and theoretical predictions to assess the sensitivity and performance of these protocols. Additionally, the thesis discusses potential future directions and advancements in the field, envisioning applications in biomolecule detection, environmental monitoring, and fundamental studies of light-matter interactions at the nanoscale. Concluding reflections highlight the implications of multiphoton quantum sensing across scientific disciplines and lay the groundwork for future research endeavors.
While the fundamental principles of light-matter interaction are well-understood and drive countless technologies, the world of multiphoton processes remains a fascinating puzzle, holding the potential to drastically alter our understanding of how light interacts with matter at its most basic level [1–4]. This rich interplay of light and matter unveils novel phenomena that can be harnessed for sensing with exceptional precision, as exemplified by multiphoton quantum sensing. This thesis delves into the applications of multiphoton quantum protocols, particularly in imaging, communication, and plasmonic sensing, to surpass classical limitations and achieve enhanced sensitivity. We explore the potential of multiphoton quantum processes, particularly in the nanoscale regime and within subsystems of macroscopic systems, where novel and ultra-sensitive sensing methodologies emerge. Subsequent chapters of this thesis demonstrate the transformative potential of multiphoton quantum sensing, elucidating the design, implementation, and experimental results of specific sensing protocols tailored to diverse applications. Our analysis combines experimental observations and theoretical predictions to assess the sensitivity and performance of these protocols. Additionally, the thesis discusses potential future directions and advancements in the field, envisioning applications in biomolecule detection, environmental monitoring, and fundamental studies of light-matter interactions at the nanoscale. Concluding reflections highlight the implications of multiphoton quantum sensing across scientific disciplines and lay the groundwork for future research endeavors.
Quantum sensing and metrology is the application of non-classical resources to the measurement of physical quantities with precision or accuracy beyond that allowed by classical physics. For many years non-classical resources such as atomic energy quantization, Josephson Effect, and Quantum Hall Effect have been used to define the fundamental units of time, voltage, and resistance, respectively. In recent years non-classical resources such as quantum squeezing and entanglement have been exploited to expand the range of physical phenomena measured with unprecedented precision or accuracy. We summarize some of the recent research on advanced quantum sensing and metrology and discuss our analyses of photon-added coherent states (PACS) of light. These analyses take into account imperfect photon addition and detection processes and show that PACS enable beyond-classical signal-to-noise ratio for photon counting even in cases where the probability of intended photon addition is 80%. We also show that there remains undiscovered fundamental properties of PACS related to their production and implementation.
Quantum optics is the branch of physics that investigates the interaction of light with matter at the quantum level, where the discrete nature of photons and quantum states of atoms, molecules, and solid-state systems become dominant. Quantum optics systems provide the experimental and theoretical foundation for understanding nonclassical states of light, quantum coherence, entanglement, and measurement at the quantum limit. Over the past few decades, advances in laser technology, nonlinear optics, and precision measurement have transformed quantum optics from a fundamental discipline into a key enabler of quantum technologies, including quantum communication, quantum computing, quantum sensing, and quantum metrology. This review presents a comprehensive overview of the physical principles, system architectures, and experimental platforms of quantum optics. Emphasis is placed on light sources, atom–photon interaction systems, detection techniques, and emerging applications, along with current challenges and future research directions.