SummaryWe present our ongoing project on Dual Comb Spectroscopy (DCS) using squeezed states of light. The primary objective of this research is to achieve a metrological advantage (MA) by applying quadrature squeezing to coherent optical frequency combs (OFCs). The squeezing will be generated using a χ(3)nonlinear photonic crystal fiber and characterized with a high-quantum-efficiency single photodiode. Optimizing the squeezing process will enable noise reduction in the interferograms produced by a novel squeezed dual comb spectroscopy technique.
SummaryWe present our ongoing project on Dual Comb Spectroscopy (DCS) using squeezed states of light. The primary objective of this research is to achieve a metrological advantage (MA) by applying quadrature squeezing to coherent optical frequency combs (OFCs). The squeezing will be generated using a χ(3)nonlinear photonic crystal fiber and characterized with a high-quantum-efficiency single photodiode. Optimizing the squeezing process will enable noise reduction in the interferograms produced by a novel squeezed dual comb spectroscopy technique.
Dual-comb spectroscopy (DCS) is a powerful technique for spectroscopic sensing, offering exceptional spectral bandwidth, resolution, precision, and speed. However, its performance is fundamentally limited by quantum noise inherent to coherent-state optical combs. Here, we overcome this barrier by introducing quantum correlation-enhanced DCS using correlated twin combs generated via seeded four-wave mixing. One comb acts as a local oscillator to decode molecular signals, while the twin suppresses shot noise through intensity-difference squeezing, achieving a 2 dB signal-to-noise ratio improvement beyond the shot-noise limit-equivalent to a 2.6× measurement speed enhancement. Notably, when coupled with up-conversion spectroscopy, our technique records comb-line-resolved, high-resolution (7.5 pm) spectra in the critical 3 μm region for molecular fingerprinting. These results bridge quantum optics and frequency comb spectroscopy, offering great potential for trace gas detection, precision metrology, and chemical analysis. Future developments in detector efficiency and nanophotonic integration could further enhance its scalability and impact.
Abstract Dual-comb spectroscopy (DCS) is a powerful technique for spectroscopic sensing, offering exceptional resolution, precision, and speed. However, its performance is fundamentally limited by quantum noise inherent to coherent-state optical combs. Here, we overcome this barrier by introducing quantum correlation-enhanced DCS using correlated twin combs generated via seeded four-wave mixing. One comb acts as a local oscillator to decode molecular signals, while the twin suppresses shot noise through intensity-difference squeezing, achieving a 2 dB signal-to-noise ratio improvement beyond the shot-noise limit—equivalent to a 2.6× measurement speed enhancement. Notably, when paired with up-conversion spectroscopy, our approach achieves comb-line-resolved, high-resolution spectra (0.0067 cm⁻¹, 7.5 pm) in the critical 3 μm region for molecular fingerprinting. These results bridge quantum optics and frequency comb spectroscopy, offering great potential for trace gas detection, precision metrology, and chemical analysis. Future developments in detector efficiency and nanophotonic integration could further enhance its scalability and impact.
Optical frequency combs have enabled distinct advantages in broadband, high-resolution spectroscopy and precision interferometry. However, quantum mechanics ultimately limits the metrological precision achievable with laser frequency combs. Quantum squeezing has led to substantial measurement improvements with continuous wave lasers, but experiments demonstrating metrological advantage with squeezed combs are less developed. Using the Kerr effect in nonlinear optical fiber, a 1-gigahertz frequency comb centered at 1560 nanometers is amplitude-squeezed by >3 decibels (dB) over a 2.5-terahertz bandwidth. Dual-comb interferometry yields mode-resolved spectroscopy of hydrogen sulfide gas with a signal-to-noise ratio nearly 3 dB beyond the shot-noise limit. The quantum noise reduction leads to a twofold quantum speedup in the determination of gas concentration, with implications for high-speed measurements of multiple species in dynamic chemical environments.
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.
Frequency combs are multimode photonic systems that underlie countless precision sensing and metrology applications. Since their invention over two decades ago, numerous efforts have pushed frequency combs to broader bandwidths and more stable operation. More recently, quantum squeezing and entanglement have been explored in single frequency comb systems for quantum advantages in sensing and signal multiplexing. However, the production of quantum light across multiple frequency combs remains unexplored. In this work, we theoretically explore a mechanism that generates a series of nonlinearly coupled frequency combs through cascaded three-wave upconversion and downconversion processes mediated by a single idler comb. We show how this system generates inter- and intracomb two-mode squeezing and entanglement spanning a very large spectral range, from ultraviolet to mid-IR frequencies. Finally, we show how this system can be engineered to produce on-demand multimode quantum light through covariance matrix optimization. Our findings could enable tunable broadband ghost spectroscopy protocols, squeezing-enhanced pump-probe measurements, and broadband entanglement between spectrally-multiplexed quanta of information.
Optical frequency combs have emerged as a cornerstone for a wide range of areas, including spectroscopy, ranging, optical clocks, time and frequency transfer, waveform synthesis, and communications. However, quantum-mechanical fluctuations of the optical carrier impose fundamental performance limits on the precision of classical optical frequency combs, particularly in their use for interferometry and spectroscopy. Entanglement, as a quintessential quantum resource, allows for surpassing the fundamental limits of classical systems. Here, we introduce entanglement into the realm of optical frequency combs, formulating entangled dual-comb spectroscopy (EDCS) that surmounts the fundamental limits of classical DCS. EDCS capitalizes on tailored entangled structures across the frequency comb, enabling simultaneous detection of all comb lines below the standard quantum limit of classical DCS. Applying EDCS in gas detection, we achieve a 2.6-dB enhancement in signal-to-noise ratio and a 1.7-fold reduction in integration time over classical DCS, rendering EDCS particularly suited for dynamic chemical and biological sensing, where fast, precise measurements subject to power constraints are required. EDCS opens a new avenue for exploiting quantum frequency combs, underscoring their prospects in a plethora of applications in precision metrology, spectroscopy, and timekeeping.