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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. 

Homodyne measurements are a widely used quantum measurement. Using a coherent state of large amplitude as the local oscillator, it can be shown that the quantum homodyne measurement limits to a field quadrature measurement. In this work, we give an example of a general idea: injecting non-classical states as a local oscillator can led to non-classical measurements. Specifically, we consider injecting a superposition of coherent states, a Schrödinger cat state, as a local oscillator. We derive the Kraus operators and the positive operator-valued measure (POVM) in this situation and show the POVM is a reflection symmetric quadrature measurement when the coherent state amplitudes are large. 

We present a new architecture for quantum-enhanced multiparameter estimation, where measured phases are cascaded along a single optical fiber. Embedded reflectors separate these phases, enabling novel fiber-based quantum distributed sensing of temperature and strain.