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.
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.
Quantum metrology takes advantage of quantum correlations to enhance the sensitivity of sensors and measurement techniques beyond their fundamental classical limit, given by the shot-noise limit. The use of both temporal and spatial correlations present in quantum states of light can extend quantum-enhanced sensing to a parallel configuration that can simultaneously probe an array of sensors or independently measure multiple parameters. To this end, we use multispatial-mode bright twin beams of light, which are characterized by independent quantum-correlated spatial subregions in addition to quantum temporal correlations, to probe a four-sensor quadrant plasmonic array. We show that it is possible to independently and simultaneously measure local changes in refractive index for all four sensors with a quantum enhancement in sensitivity in the range of 22% to 24% over the corresponding classical configuration. These results provide a first step toward highly parallel spatially resolved quantum-enhanced sensing techniques and pave the way toward more complex quantum sensing and quantum imaging platforms.
Quantum resources can enhance the sensitivity of a device beyond the classical shot noise limit and, as a result, revolutionize the field of metrology through the development of quantum-enhanced sensors. In particular, plasmonic sensors, which are widely used in biological and chemical sensing applications, offer a unique opportunity to bring such an enhancement to real-life devices. Here, we use bright entangled twin beams to enhance the sensitivity of a plasmonic sensor used to measure local changes in refractive index. We demonstrate a 56% quantum enhancement in the sensitivity of state-of-the-art plasmonic sensor with measured sensitivities on the order of 10−10RIU/Hz, nearly 5 orders of magnitude better than previous proof-of-principle implementations of quantum-enhanced plasmonic sensors. These results promise significant enhancements in ultratrace label free plasmonic sensing and will find their way into areas ranging from biomedical applications to chemical detection.
Quantum metrology leverages quantum resources to surpass classical limits in measurement sensitivity, enabling new capabilities across fields ranging from fundamental physics to sensing, imaging, and navigation. As these techniques mature, an increasing emphasis is being placed on translating quantum-enhanced performance into practical, robust systems that can operate outside controlled laboratory environments. The overarching objective of the work presented in this dissertation is to develop sensing platforms that achieve improved performance by leveraging quantum resources in realistic, noisy environments. In particular, this work focuses on the use of squeezed states of light, and investigates how two-mode squeezed states generated through four-wave mixing can be developed into compact sources and integrated with practical fiber-optic and plasmonic sensing platforms. Squeezed states of light, and in particular two-mode squeezed states (twin beams), constitute a powerful resource in quantum metrology. Their reduced quantum noise enables measurements below the noise level that can be achieved with classical resources, know as the shot-noise limit, offering genuine quantum advantages in precision sensing and measurement. Beyond their fundamental interest, such states provide a pathway toward practical quantum technologies capable of outperforming classical approaches in real-world applications. For many practical implementations, it is therefore highly advantageous to demonstrate squeezed light sources that are compact, stable, and compatible with existing photonic infrastructures. This is needed to lower the barrier to incorporate quantum resources into experiments and sensing platforms, particularly in environments where bulky or delicate optical setups are impractical. To demonstrate a pathway toward practical quantum sensing with squeezed light, this dissertation presents experimental studies spanning both the development of deployable squeezed-light sources and their application in practical or real-world sensing platforms. We present the development of a compact, narrowband, fiber-coupled source of squeezed light based on four-wave mixing in hot Rb 85 vapor. The system achieves more than 4 dB of intensity-difference squeezing after propagation through polarization-maintaining fibers, demonstrating that strong quantum correlations can be preserved even when fiber coupled. This platform serves as a standalone proof-of-principle demonstration of a deployable, low–size, weight, and power (low-SWaP) squeezed-light source that is well suited for applications where fiber delivery of quantum-correlated light can be readily integrated into existing experimental and sensing platforms. In addition to this source development, the dissertation investigates two distinct applications of twin-beam for quantum-enhanced sensing. The first one focuses on fiber Bragg grating (FBG) sensors, which are widely used to monitor strain, vibration, and temperature in applications ranging from civil infrastructure and aerospace systems to oil and gas pipeline monitoring. By coupling the squeezed light into separate FBGs and employing differential detection, common-mode noise is suppressed while localized perturbations are retained. This work provides a feasibility study for using twin-beams to enhance the sensitivity of FBG-based sensors beyond classical limits while providing robustness against environmental noise. The second application examines plasmonic sensors based on surface plasmon resonances in metallic nanostructures, which enable highly sensitive detection of small changes in refractive index. Such plasmonic sensors are particularly useful for applications in chemical and biological sensing, environmental monitoring, and lab-on-chip platforms, where compactness and high sensitivity to refractive index changes are critical. A dual-probing scheme is introduced in which both beams of a two-mode squeezed state interact with a polarization-dependent plasmonic nanostructure. By exploiting opposite spectral response for orthogonal polarizations, this approach improves measurement sensitivity relative to our previous technique of using one beam to probe the plasmonic sensor and the other to serve as a reference. This new technique takes advantage of transducing information into both the beams while preserving the benefits of differential detection for noise cancellation. Taken together, these studies illustrate complementary approaches for leveraging quantum correlations for practical sensing problems. Through the development of a compact, fiber-compatible squeezed-light source and independent demonstrations of enhanced performance in both fiber-optic and plasmonic sensors, this dissertation advances pathways for translating quantum sensing approaches based on quantum states of light from laboratory demonstrations into deployable metrology tools.
The ultimate sensitivity of any optically based measurement using classical resources (for example, laser or thermal light) is constrained by the photon shot noise limit (SNL). However, quantum states of light, in which photon pairs have quantum correlations or entanglement, off er a path beyond this limit. In particular, “squeezing” in these quantum states makes it possible to lower the noise in the detection system below the SNL. This can signifi cantly enhance the sensitivity of real-world devices and could thus revolutionize optical-based sensing applications
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.