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.
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.
Quantum resources such as squeezed and entangled states of light provide a pathway to surpass classical sensitivity limits in measurement and information processing. This thesis presents the development and application of engineered squeezed light sources across both bulk and integrated photonic platforms, demonstrating their utility in advancing quantum-enhanced metrology for spectroscopy and inertial sensing. In the first experimental platform, I introduce entangled dual-comb spectroscopy (EDCS), which integrates squeezed light with dual-comb architectures. By exploiting entanglement across comb lines, EDCS circumvents the shot-noise limitations of classical dual-comb spectroscopy. My experiment demonstrate a 2.6 dB improvement in signal-to-noise ratio and a 1.7-fold reduction in integration time, establishing EDCS as a powerful tool for rapid and precise chemical and biological sensing. The second platform applies squeezed light to resonant fiber optic gyroscopes (RFOGs), where quantum fluctuations typically impose a fundamental noise floor. By injecting bright amplitude-squeezed light into the resonator, I achieve a 2 dB reduction in detector noise, verified via Allan deviation analysis. This quantum-enhanced RFOG architecture shows that squeezed light can improve sensitivity under practical operational conditions, paving the way for next-generation inertial navigation systems. Finally, I demonstrate the on-chip generation of squeezed light using silicon nitride photonic circuits. Thin-film devices achieve more than 2 dB of quadrature squeezing with excellent agreement between experiment and theory, while wafer-scale thick-film devices yield reproducible 3 dB squeezing across multiple dies with sub-0.2 dB variation. These results establish silicon nitride as a CMOS-compatible platform for scalable and manufacturable quantum light sources, offering a route toward robust, large-scale quantum photonic technologies. Together, these results bridge the gap between laboratory demonstrations and deployable quantum-enhanced measurement systems. By advancing both free-space and integrated implementations of squeezed light, this work provides foundational steps toward practical quantum technologies for precision navigation, spectroscopy, and information processing.
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-correlated states of light, such as squeezed states, constitute a fundamental resource for quantum technologies, enabling enhanced performance in quantum metrology, quantum information processing, and quantum communications. The practical deployment of such technologies requires squeezed-light sources that are compact, efficient, low-cost, and robust. Here we report a compact narrowband source of two-mode squeezed light at 795 nm based on four-wave mixing in hot 85Rb atomic vapor. The source is implemented in a small, modular architecture featuring a single fiber-coupled input, an electro-optic phase modulator combined with a single Fabry-Perot etalon for probe generation, and two free-space output modes corresponding to the signal and conjugate fields. Optimized for low pump power, the system achieves up to -8 dB of intensity-difference squeezing at an analysis frequency of 0.8 MHz with a pump power of only 300 mW. The intrinsic narrowband character of the generated quantum states makes this source particularly well suited for atomic-based quantum sensing and quantum networking, including interfaces with atomic quantum memories. Our results establish a versatile and portable platform for low-SWaP squeezed-light generation, paving the way toward deployable quantum-enhanced technologies.
Quantum correlated states of light, such as squeezed states, are a fundamental resource for the development of quantum technologies, as they are needed for applications in quantum metrology, quantum computation, and quantum communications. It is thus critical to develop compact, efficient, and robust sources to generate such states. Here, we report on a compact, narrowband, fiber-coupled source of two-mode squeezed states of light at 795 nm based on four-wave mixing (FWM) in an 85Rb atomic vapor. The source is designed in a small modular form factor, with two input fiber-coupled beams, the seed and pump beams required for the FWM, and two output fibers, one for each of the modes of the squeezed state. The system is optimized for low pump power (135 mW) to achieve a maximum intensity-difference squeezing of 4.4 dB after the output of fibers at an analysis frequency of 1 MHz. The narrowband nature of the source makes it ideal for atomic-based quantum sensing and quantum networking configurations that rely on atomic quantum memories. Such a source paves the way for a versatile and portable platform for applications in quantum information science.
Multi-photon nonlinear processes in atoms have served as important tools for quantum metrology, quantum communications, and quantum sensing. In this thesis, we experimentally address the interplay of various multi-photon Raman processes in hot Rb vapor, with the four-wave mixing (FWM) process being a central theme. FWM is the nonlinear response of a medium to a strong optical pump field inelastically scattering off atomic resonances and resulting in the generation of additional photons in different modes. FWM is a detrimental, but inherent part of electromagnetically induced transparency (EIT) and Raman based quantum memories. However, we were able to weaken the four-photon resonance by utilizing two-photon absorption to remove the additional photons without interfering with the signal beam. We also demonstrate the ability to tailor FWM to generate new photons in a controlled fashion for mode conversion. With this, we showed the conversion of 795 nm light to 420 nm light. While FWM is a source of noise in quantum memories, it can also be used for the generation squeezed twin-beams. Such beams have relative intensity noise reduced below the classical shot noise limit and share mode dependence based on the phase-matching conditions. Using this, we demonstrated that twin-beams can be generated with largely different spatial structure (optical angular momentum) and still share strong correlations, so long as the phase-matching conditions are satisfied. We then constructed and demonstrated the operation of a polarization-based quantum interferometer using squeezed twin-beams and showed that our beams were entangled under the inseparability condition. Using this interferometer, we were also able to achieve squeezing at low detection frequencies, which is necessary for things like quantum imaging and gravitational wave detection. We also demonstrated that squeezed twin-beams can be utilized to enhance the sensitivity of two-photon absorption spectroscopy. This research has touched on many different subjects related to quantum information science and improved upon some of the tools needed for the implementation of such technologies.
Squeezed light is expected to enable new quantum metrology and quantum computation applications, but the very high degree of experimental control required in practice places severe demands on the physical devices used to generate it. As ultrafast squeezed light sources are reaching an unprecedented degree of brightness and modal control, there is a strong interest in developing methods for their experimental characterization and theoretical understanding. In this thesis, we demonstrate both a new application and a new characterization technique for pulsed squeezed light. In the first part of the thesis, we present a new metrological application of pulsed squeezed light: quantum-enhanced label-free nonlinear microscopy. Stimulated emission microscopy (SEM) is a state-of-the-art pump-probe microscopy technique whose sensitivity is ultimately limited by shot noise in the probe beam. We propose to overcome this fundamental limitation by using a sub-Poissonian probe generated via optical parametric amplification. We demonstrate an intensity-squeezed sub-picosecond pulsed probe, and a simple stimulated emission microscope. Using this squeezed probe, sub-Poissonian statistics are observed in the SEM signal. After this proof-of-principle experiment, we aim to provide an improved design for a source of intensity-squeezed light. First, we develop a theoretical framework to simulate the photon statistics of a general sub-Poissonian source, considering pulsed and focused pump and seed fields in a unified spatio-temporal description. Next, we use this framework to suggest possible improvements to our previous squeezed probe. In the second part of this thesis, we provide new theoretical and experimental tools to analyze the high gain regime of pulsed spontaneous parametric down-conversion (SPDC). We study a waveguided source capable of generating twin-beams with tens of photons in a single spatio-temporal mode. We develop a framework to efficiently simulate SPDC for an arbitrary nonlinear gain, including the effect of parasitic nonlinearities such as self-phase modulation (SPM) of the pump and cross-phase modulation (XPM) between pump and twin-beams. We experimentally characterize our source using a new technique based on stimulated difference-frequency generation (DFG). In a type-II down-conversion process, we measure the frequency generation produced not only in the orthogonal polarization to the seeding beam, but also in its same polarization, which we interpret as cascaded difference-frequency generation. We argue that the additional information obtained in this measurement allows for a self-referenced estimation of the squeezing gain. Using these measurements, we accurately fit our theoretical model, revealing that, in the high gain regime, parasitic nonlinearities strongly affect the spectral structure of the twin-beams. We propose a simple strategy to reduce the impact of these nonlinearities on the modal structure of SPDC.