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arXiv:2412.19800 · Physical Review X

Entangled Dual-Comb Spectroscopy

Abdulkarim Hariri, Shuai Liu, Haowei Shi, Quntao Zhuang, Xudong Fan, Zheshen Zhang

Published Aug 28, 2025• 9 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/plh2-cr8s

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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.
Abstract Dual-comb interferometry harnesses the interference of two laser frequency combs to provide unprecedented capability in spectroscopy applications. In the past decade, the state-of-the-art systems have reached a point where the signal-to-noise ratio per unit acquisition time is fundamentally limited by shot noise from vacuum fluctuations. To address the issue, we propose an entanglement-enhanced dual-comb spectroscopy protocol that leverages quantum resources to significantly improve the signal-to-noise ratio performance. To analyze the performance of real systems, we develop a quantum model of dual-comb spectroscopy that takes practical noises into consideration. Based on this model, we propose quantum combs with side-band entanglement around each comb lines to suppress the shot noise in heterodyne detection. Our results show significant quantum advantages in the uW to mW power range, making this technique particularly attractive for biological and chemical sensing applications. Furthermore, the quantum comb can be engineered using nonlinear optics and promises near-term experimentation.
We propose distributed dual-comb spectroscopy, a quantum-enhanced sensing architecture that simultaneously exploits spatial- and spectral-domain entanglement to improve the extraction of global spectroscopic information across broadband frequency ranges. Our scheme consists of a network of Mach-Zehnder interferometers interrogating spatially separated samples, each driven by a classical frequency comb at the bright port. A single two-mode squeezed frequency comb is distributed through a passive beam-splitter array into KKK entangled combs, establishing multipartite correlations across sensors while preserving intrinsic spectral entanglement. The protocol is compatible with both heterodyne detection and division detection, and enables parallel estimation of weighted-average absorption features over multiple frequency components. Compared with spatially separable quantum strategies requiring KKK independently engineered nonclassical comb sources, our approach achieves enhanced signal-to-noise performance using only a single quantum resource distributed across the network. These results establish a scalable route toward broadband distributed quantum spectroscopy with simultaneous spatial and spectral advantage.
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.
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.