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Data from: Squeezed dual-comb spectroscopy

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Jan 17, 2025 version files 72.99 GB

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Abstract

Laser spectroscopy and interferometry provide an unparalleled view into the fundamental nature of matter and the Universe through ultra-precise measurements of atomic transition frequencies and gravitational waves. Optical frequency combs have expanded metrology capabilities by phase-coherently bridging radio frequency and optical domains to enable traceable high-resolution spectroscopy across bandwidths greater than hundreds of terahertz. However, quantum mechanics limits the measurement precision achievable with laser frequency combs and traditional laser sources, ultimately impacting fundamental interferometry and spectroscopy. Squeezing the distribution of quantum noise to enhance measurement precision of either the amplitude or phase quadrature of an optical field leads to significant measurement improvements with continuous wave lasers. But experiments demonstrating true metrological advantage of broad bandwidth squeezing with optical frequency combs are much less developed. In this work, we generate bright amplitude-squeezed frequency comb light and apply it to molecular spectroscopy using interferometry that leverages the high-speed and broad spectral coverage of the dual-comb technique. Using the Kerr effect in nonlinear optical fiber, the amplitude quadrature of a frequency comb centered at 1560 nm is squeezed by >3 dB over a 2.5 THz of bandwidth that includes 2500 comb teeth spaced by 1 GHz. Interferometry with a second coherent state frequency comb yields mode-resolved spectroscopy of hydrogen sulfide gas with a signal-to-noise ratio nearly 3 dB beyond the shot noise limit, taking full metrological advantage of the amplitude squeezing when the electrical noise floor is considered. The quantum noise reduction leads to a two-fold quantum speedup in the determination of gas concentration, with impact for fast, broadband, and high signal-to-noise ratio measurements of multiple species in dynamic chemical and biological environments. Overall, this work solidifies the general understanding of quantum noise reduction in Fourier transform spectroscopy and motivates further exploration with squeezed states in the broad application space of frequency comb metrology.