Quantum plasmonics explores how light interacts with collective charge oscillations at metal-dielectric interfaces, enabling strong confinement and enhanced quantum effects at the nanoscale. While traditional quantum optics focuses on single photons, this thesis explores an intermediate regime - multiparticle quantum optics - where classical light, analyzed using photon-number-resolving detection and projective measurements, reveals nontrivial quantum correlations. We begin by establishing the theoretical foundation of multiparticle quantum plasmonics, introducing key concepts like photon-plasmon interactions, coherence, and statistical fluctuations. The first study shows that multiparticle scattering can alter quantum statistics in plasmonic systems, offering new control over fluctuations. The second reveals nonclassical near-field plasmon dynamics, showing how quantum coherence emerges from bosonic and fermionic contributions in subsystems. The third study presents a quantum plasmonic sensing method, using conditional detection to boost signal-to-noise ratio and improve phase estimation. The final study extends this approach to quantum imaging with natural light: by isolating multiphoton correlations from thermal light via photon-number-resolving detection and a single-pixel protocol, we enhance image contrast under noisy conditions. These results show that multiparticle interactions can control quantum statistical properties, even in classical fields. By bridging theory and application, this thesis advances quantum plasmonics and highlights the potential of multiphoton methods in imaging, sensing, and information processing.
Quantum plasmonics explores how light interacts with collective charge oscillations at metal-dielectric interfaces, enabling strong confinement and enhanced quantum effects at the nanoscale. While traditional quantum optics focuses on single photons, this thesis explores an intermediate regime - multiparticle quantum optics - where classical light, analyzed using photon-number-resolving detection and projective measurements, reveals nontrivial quantum correlations. We begin by establishing the theoretical foundation of multiparticle quantum plasmonics, introducing key concepts like photon-plasmon interactions, coherence, and statistical fluctuations. The first study shows that multiparticle scattering can alter quantum statistics in plasmonic systems, offering new control over fluctuations. The second reveals nonclassical near-field plasmon dynamics, showing how quantum coherence emerges from bosonic and fermionic contributions in subsystems. The third study presents a quantum plasmonic sensing method, using conditional detection to boost signal-to-noise ratio and improve phase estimation. The final study extends this approach to quantum imaging with natural light: by isolating multiphoton correlations from thermal light via photon-number-resolving detection and a single-pixel protocol, we enhance image contrast under noisy conditions. These results show that multiparticle interactions can control quantum statistical properties, even in classical fields. By bridging theory and application, this thesis advances quantum plasmonics and highlights the potential of multiphoton methods in imaging, sensing, and information processing.
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.
In the field of optics and photonics, plasmonic sensors have garnered considerable interest due to their outstanding sensitivity and impressive capacity to control light at the nanoscale. These sensors enable the integration of biochemical sensing platforms by exploiting the combination of enhanced and localized electromagnetic fields at the metal–dielectric interface, and they operate effectively below the diffraction limit. The performance of conventional plasmonic sensors, despite their practical development and commercial success, remains inherently constrained by classical noise constraints, owing to the quantum fluctuations of light, known as the shot-noise limit. Recent advances have introduced quantum optical resources such as entangled and squeezed light states to overcome inherent classical restrictions, thus giving rise to the quantum plasmonic sensing field. This interdisciplinary field combines the ability to enhance electric field capabilities with the precision of quantum metrology, enabling ultrasensitive chemical and biological detection that surpasses classical precision thresholds. In the last decades, theoretical models and experimental demonstrations have greatly advanced the development of quantum plasmonic sensors, improving our comprehension of quantum light–matter interactions and facilitating novel nanoscale sensing designs. This chapter provides a comprehensive overview of the fundamental principles, latest developments, and major concepts that have driven progress in quantum plasmonic sensing and shows that quantum components are being integrated into plasmonic systems, thereby transforming optical sensing to the quantum level.
Quantum sensing is an emerging field of quantum optics that seeks to take advantage of quantum correlations available in quantum states of light to enable sensitivities beyond the fundamental classical limits. \nThe sensitivity of measurements and sensing apparatus when using classical states of light is limited to the shot-noise limit (SNL), which is achieved with coherent states of light. \n \nTwo-mode squeezed states of light (twin beams) have quantum correlations both in time and space, leading to temporal and spatial squeezing properties. \nSeveral applications can benefit from such noise reduction to enable new approaches, such as quantum-enhanced interferometry, quantum imaging, and quantum sensing. \nThe emergence of quantum technologies has been referred to as the second quantum revolution. \nFor metrology and sensing applications, in particular, it has led to new state-of-the-art sensitivity limits. \n \nIn this thesis, we discuss the implementation of quantum sensing based on squeezed states of light and plasmonic sensors as a platform for the demonstration of real-life quantum sensing. \nWe present a quantum-enhanced plasmonic sensing setup that can detect changes in the refractive index of air beyond the SNL. \nFurthermore, we generalize such experimental apparatus to probe an array of sensors using the quantum correlations present in different spatial locations to demonstrate a parallel quantum-enhanced plasmonic sensing scheme that can simultaneously detect changes in the refractive index of air in multiple locations with a single probing beam. \nThese results prove the applicability of twin beams for real-life applications based on plasmonic sensors. \nThe spatially resolved sensing scheme can be extended to pixel-size sensing of multiple sensors for multi-parameter estimation and detection applications to reach more complex sensing architectures.
The possibility of using weak optical signals to perform sensing of delicate samples constitutes one of the main goals of quantum photonic sensing. Furthermore, the nanoscale confinement of electromagnetic near fields in photonic platforms through surface plasmon polaritons has motivated the development of highly sensitive quantum plasmonic sensors. Despite the enormous potential of plasmonic platforms for sensing, this class of sensors is ultimately limited by the quantum statistical fluctuations of surface plasmons. Indeed, the fluctuations of the electromagnetic field severely limit the performance of quantum plasmonic sensing platforms in which delicate samples are characterized using weak near-field signals. Furthermore, the inherent losses associated with plasmonic fields levy additional constraints that challenge the realization of sensitivities beyond the shot-noise limit. Here, we introduce a protocol for quantum plasmonic sensing based on the conditional detection of plasmons. We demonstrate that the conditional detection of plasmonic fields, via plasmon subtraction, provides a new degree of freedom to control quantum fluctuations of plasmonic fields. This mechanism enables improvement of the signal-to-noise ratio of photonic sensors relying on plasmonic signals that are comparable to their associated field fluctuations. Consequently, the possibility of using weak plasmonic signals to sense delicate samples, while preserving the sample properties, has important implications for molecule sensing, and chemical detection.
The extraordinary sensitivity of plasmonic sensors is well-known in the optics and photonics community. These sensors exploit simultaneously the enhancement and the localization of electromagnetic fields close to the interface between a metal and a dielectric. This enables, for example, the design of integrated biochemical sensors at scales far below the diffraction limit. Despite their practical realization and successful commercialization, the sensitivity and associated precision of plasmonic sensors are starting to reach their fundamental classical limit given by quantum fluctuations of light-known as the shot-noise limit. To improve the sensing performance of these sensors beyond the classical limit, quantum resources are increasingly being employed. This area of research has become known as "quantum plasmonic sensing", and it has experienced substantial activity in recent years for applications in chemical and biological sensing. This review aims to cover both plasmonic and quantum techniques for sensing, and it shows how they have been merged to enhance the performance of plasmonic sensors beyond traditional methods. We discuss the general framework developed for quantum plasmonic sensing in recent years, covering the basic theory behind the advancements made, and describe the important works that made these advancements. We also describe several key works in detail, highlighting their motivation, the working principles behind them, and their future impact. The intention of the review is to set a foundation for a burgeoning field of research that is currently being explored out of intellectual curiosity and for a wide range of practical applications in biochemistry, medicine, and pharmaceutical research.