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 $K$ 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 $K$ 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.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 $K$ 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 $K$ 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.

quant-pharXiv:2610.30462Oct 23, 20260 citations

Fundamental Limits of Optical Frequency Comb Interferometry and Spectroscopy with Coherent, Thermal, and Quantum Light

Tsao, Eugene J.

The measurement and manipulation of coherent optical fields have been transformed by the optical frequency comb. Today, the optical frequency comb grants measurements precise enough to count individual cycles of light as well as the generation of nearly any coherent electromagnetic field from the ultraviolet through the infrared. These capabilities have enabled the most precise realizations and comparisons of time, precision spectroscopy over broad bandwidths, and the ability to convert stable signals between optical and microwave fields–seamlessly connecting the entire electromagnetic spectrum from hertz (100 ) to petahertz (1015). These applications involve the interference of a frequency comb with another coherent light source, such as another frequency comb or a single-frequency continuous-wave laser. However, coherent light represents only one type of light. The vast majority of light emanates from “black bodies” such as stars, which is in a thermal state as opposed to a coherent state, and carries profound information about the universe and humanity’s place within it. Other types of light defy classical electromagnetism and are known as non-classical or quantum light. Such quantum light may play central roles in quantum communication, quantum computation, and quantum-enhanced metrology. In this thesis, the use of the optical frequency comb in the interferometric measurement of thermal and quantum light is investigated, with a focus on assessing fundamental limits to the sensitivity of such measurements. In order to measure thermal light, a technique called dual-comb correlation spectroscopy is explored. This technique entails heterodyne measurement of the field of thermal light and subsequent correlation of the field in time. This process reveals the spectrum of thermal light at high resolution and across broad bandwidths. New theoretical work uncovers previously unknown fundamental limits on sensitivity when measuring realistically weak thermal light. Experimental investigation verifies this scaling and is accompanied by a demonstration of spectroscopy at the equivalent power spectral density of our Sun, realizing a greater than 1000-fold sensitivity increase over past demonstrations of this technique. These insights pave the way for expansion of this technique to comb-based spatial correlation of thermal fields. This advancement would allow for extended baseline synthetic aperture hyperspectral imaging throughout the optical spectrum, facilitating novel and profound observations of the universe. The use of frequency combs for the measurement of quantum light is also investigated. This scenario breaks typical quantum optics assumptions, such as large, mode-matched local oscillators, and necessitates new quantum measurement operators. Such measurement operators are derived, which not only describe homodyne measurements on any quantum state of light with a frequency comb local oscillator, but also indicate that the shot noise limit generally reached in comb-based measurements of coherent light (such as in continuous-wave laser heterodyne and dual-comb spectroscopy) does not correspond to the quadrature or coherent state-overlap description standard in quantum optics. Efforts to experimentally reach this “standard” quantum limit demonstrate a significant improvement in the signal-to-noise ratio over the conventional comb-based shot noise limit, paving the way for lower-power portable optical clocks and quantum-enhanced frequencycomb metrology.The measurement and manipulation of coherent optical fields have been transformed by the optical frequency comb. Today, the optical frequency comb grants measurements precise enough to count individual cycles of light as well as the generation of nearly any coherent electromagnetic field from the ultraviolet through the infrared. These capabilities have enabled the most precise realizations and comparisons of time, precision spectroscopy over broad bandwidths, and the ability to convert stable signals between optical and microwave fields–seamlessly connecting the entire electromagnetic spectrum from hertz (100 ) to petahertz (1015). These applications involve the interference of a frequency comb with another coherent light source, such as another frequency comb or a single-frequency continuous-wave laser. However, coherent light represents only one type of light. The vast majority of light emanates from “black bodies” such as stars, which is in a thermal state as opposed to a coherent state, and carries profound information about the universe and humanity’s place within it. Other types of light defy classical electromagnetism and are known as non-classical or quantum light. Such quantum light may play central roles in quantum communication, quantum computation, and quantum-enhanced metrology. In this thesis, the use of the optical frequency comb in the interferometric measurement of thermal and quantum light is investigated, with a focus on assessing fundamental limits to the sensitivity of such measurements. In order to measure thermal light, a technique called dual-comb correlation spectroscopy is explored. This technique entails heterodyne measurement of the field of thermal light and subsequent correlation of the field in time. This process reveals the spectrum of thermal light at high resolution and across broad bandwidths. New theoretical work uncovers previously unknown fundamental limits on sensitivity when measuring realistically weak thermal light. Experimental investigation verifies this scaling and is accompanied by a demonstration of spectroscopy at the equivalent power spectral density of our Sun, realizing a greater than 1000-fold sensitivity increase over past demonstrations of this technique. These insights pave the way for expansion of this technique to comb-based spatial correlation of thermal fields. This advancement would allow for extended baseline synthetic aperture hyperspectral imaging throughout the optical spectrum, facilitating novel and profound observations of the universe. The use of frequency combs for the measurement of quantum light is also investigated. This scenario breaks typical quantum optics assumptions, such as large, mode-matched local oscillators, and necessitates new quantum measurement operators. Such measurement operators are derived, which not only describe homodyne measurements on any quantum state of light with a frequency comb local oscillator, but also indicate that the shot noise limit generally reached in comb-based measurements of coherent light (such as in continuous-wave laser heterodyne and dual-comb spectroscopy) does not correspond to the quadrature or coherent state-overlap description standard in quantum optics. Efforts to experimentally reach this “standard” quantum limit demonstrate a significant improvement in the signal-to-noise ratio over the conventional comb-based shot noise limit, paving the way for lower-power portable optical clocks and quantum-enhanced frequencycomb metrology.

Nov 20, 20240 citations

Heterodyne detection in the presence of degraded laser beams

James Porter Moreland, S. Collins

IEEE Journal of Quantum ElectronicsApr 1, 19660 citations

Theory of three-pulse photon echo spectroscopy with dual frequency combs

Jonggu Jeon, JunWoo Kim, Tai Hyun Yoon +1 more

A theoretical analysis is carried out for the recently developed three-pulse photon echo spectroscopy employing dual frequency combs (DFC) as the light sources. In this method, the molecular sample interacts with three pulse trains derived from the DFC, and the generated third-order signal is displayed as a two-dimensional (2D) spectrum that depends on the waiting time introduced by employing the asynchronous optical sampling method. Through the analysis of the heterodyne-detected signal interferogram using a local oscillator derived from one of the optical frequency combs, we show that the 2D spectrum closely matches the spectrum expected from a conventional approach with four pulses derived from a single femtosecond laser pulse, and the waiting time between the second and third field-matter interactions is given by the down-converted detection time of the interferogram. The theoretical result is applied to a two-level model system with solvation effect described by solvatochromic spectral density. The model 2D spectrum reproduces spectral features such as the loss of frequency correlation, dephasing, and spectral shift as a function of the population time. We anticipate that the present theory will be the general framework for quantitative descriptions of DFC-based nonlinear optical spectroscopy.A theoretical analysis is carried out for the recently developed three-pulse photon echo spectroscopy employing dual frequency combs (DFC) as the light sources. In this method, the molecular sample interacts with three pulse trains derived from the DFC, and the generated third-order signal is displayed as a two-dimensional (2D) spectrum that depends on the waiting time introduced by employing the asynchronous optical sampling method. Through the analysis of the heterodyne-detected signal interferogram using a local oscillator derived from one of the optical frequency combs, we show that the 2D spectrum closely matches the spectrum expected from a conventional approach with four pulses derived from a single femtosecond laser pulse, and the waiting time between the second and third field-matter interactions is given by the down-converted detection time of the interferogram. The theoretical result is applied to a two-level model system with solvation effect described by solvatochromic spectral density. The model 2D spectrum reproduces spectral features such as the loss of frequency correlation, dephasing, and spectral shift as a function of the population time. We anticipate that the present theory will be the general framework for quantitative descriptions of DFC-based nonlinear optical spectroscopy.

arXiv:1905.11687Journal of the Optical Society of America BOct 25, 20195 citations

Second-Order Coherence Effects in Optical Heterodyne Detection

Ichiro Sakuraba

北海道大學工學部研究報告 = Bulletin of the Faculty of Engineering, Hokkaido UniversityMar 30, 19720 citations

K

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

K

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.