Proceedings of the National Academy of Sciences

Quantum-enhanced sensing of molecular excited-state dynamics with correlated photons

Jiahao Fan, Feihong Liu, Dangyuan Lei, Shaul Mukamel, Zhedong Zhang

Published Oct 15, 2026• 0 citations

Abstract

Squeezed photons, which provide a quantum-correlated light with reduced noise, have emerged as a powerful resource for sensing the structures of matter. Here, we study the pump-probe scheme using squeezed photons whose spectral correlation of amplitudes can be tailored. A microscopic theory reveals a highly time-energy-resolved signal that is not attainable by classical pump-probe scheme. The results show high selectivity of accessing the molecular correlation functions, e.g., suppression of ground-state bleaching signal, and can significantly enhance signal intensity that surpasses the bottleneck by entangled twin photons. An application to a monolayer semiconductor model reveals a real-time monitoring of valley excitons and their dynamics, i.e., conversion between dark and bright excitons. We further show the intermediate squeezing regime-not strong squeezing-where time-resolved spectroscopy is favorable. Our work offers a paradigm for studying nonequilibrium dynamics of matter, in photocatalysis and optoelectronics.

DOI: 10.1073/pnas.2609628123

Related papers

Quantum-Enhanced Sensing of Excited-State Dynamics with Correlated Photons

Jiahao Fan, Feihong Liu, Dangyuan Lei +1 more

The squeezed photons, as a quantum-correlated light with reduced noise, have emerged as a great resource for sensing the structures of matter. Here we study the transient absorption (TA) scheme using the squeezed photons whose spectral correlation of amplitudes can be tailored. A microscopic theory is developed, revealing a highly time-energy-resolved nature of the signal that is not attainable by conventional TA scheme. Such a capability is elaborated by applying to monolayer transition metal dichalcogenide materials (TMDs), achieving a real-time monitoring of valley excitons and their dynamics. Moreover, we show the intermediate squeezing regime-not the strong squeezing-which the time-resolved spectroscopy is in favor of. Our work offers a new paradigm for studying nonequilibrium dynamics of matter, in light of the photocatalysis and optoelectronics.

arXiv:2508.11311Aug 15, 20250 citations

Probing exciton dynamics with spectral selectivity through the use of quantum entangled photons

Yuta Fujihashi, Kuniyuki Miwa, Masahiro Higashi +1 more

Quantum light is increasingly recognized as a promising resource for developing optical measurement techniques. Particular attention has been paid to enhancing the precision of the measurements beyond classical techniques by using nonclassical correlations between quantum entangled photons. Recent advances in the quantum optics technology have made it possible to manipulate spectral and temporal properties of entangled photons, and photon correlations can facilitate the extraction of matter information with relatively simple optical systems compared to conventional schemes. In these respects, the applications of entangled photons to time-resolved spectroscopy can open new avenues for unambiguously extracting information on dynamical processes in complex molecular and materials systems. Here, we propose time-resolved spectroscopy in which specific signal contributions are selectively enhanced by harnessing nonclassical correlations of entangled photons. The entanglement time characterizes the mutual delay between an entangled twin and determines the spectral distribution of photon correlations. The entanglement time plays a dual role as the knob for controlling the accessible time region of dynamical processes and the degrees of spectral selectivity. In this sense, the role of the entanglement time is substantially equivalent to the temporal width of the classical laser pulse. The results demonstrate that the application of quantum entangled photons to time-resolved spectroscopy leads to monitoring dynamical processes in complex molecular and materials systems by selectively extracting desired signal contributions from congested spectra. We anticipate that more elaborately engineered photon states would broaden the availability of quantum light spectroscopy.

arXiv:2212.11519The Journal of Chemical PhysicsSep 15, 202315 citations

Quantum-enhanced coherent Raman spectroscopy with broadband squeezed-light detection

Konstantin E. Dorfman, Vladislav V. Yakovlev, Shaul Mukamel

Quantum correlations offer the possibility of surpassing classical limits in optical measurements, but their integration into nonlinear vibrational spectroscopy has remained largely unexplored. Here, we introduce a quantum-enhanced implementation of coherent Raman spectroscopy that employs broadband squeezed-light detection to interrogate relative intensity correlations between Stokes and anti-Stokes fields generated in an ultrafast four-wave-mixing process. By exploiting nonclassical correlations between these fields, we suppress the nonresonant background and enhance the signal-to-noise performance in both temporal and spectral domains, enabling detection sensitivities beyond the classical shot-noise limit. Importantly, the quantum advantage demonstrated here does not arise solely from improved detection statistics. Rather, it originates from microscopic intermolecular correlations mediated by cascaded exchange of a virtual photon between molecular pairs. This mechanism establishes a fundamentally distinct and significant pathway for information extraction in vibrational spectroscopy, providing access to structural and dynamical observables that are intrinsically inaccessible by conventional classical Raman techniques. Numerical simulations illustrate the power of the technique by resolving intradimer [Formula: see text] bond splitting in cyclobutane thymine dimers following ultraviolet excitation, highlighting its potential for probing ultrafast photochemical processes with quantum-limited sensitivity and for label-free biomedical optical sensing and imaging.

Proceedings of the National Academy of SciencesSep 8, 20260 citations

Entangled photons enabled ultrafast stimulated Raman spectroscopy for molecular dynamics

Jiahao Fan, Z. Y. Ou, Zhedong Zhang

Quantum entanglement has emerged as a great resource for studying the interactions between molecules and radiation. We propose a new scheme of stimulated Raman scattering with entangled photons. A quantum ultrafast Raman spectroscopy is developed for condensed-phase molecules, to monitor the exciton populations and coherences. Analytic results are obtained, showing an entanglement-enabled time-frequency scale not attainable by classical light. The Raman signal presents an unprecedented selectivity of molecular correlation functions, as a result of the Hong-Ou-Mandel interference. Our work suggests a new paradigm of using an unconventional interferometer as part of spectroscopy, with the potential to unveil advanced information about complex materials.

arXiv:2305.14661Light Science & ApplicationsJul 14, 202437 citations

Ultrafast optical spectroscopy with quantum light and quantum control

Jiahao Fan, Xiu–Hao Deng, Zhedong Zhang

Classical light such as lasers and thermal radiation has long been utilized for spectroscopy to explore material structures and dynamics. However, quantum states of light open new avenues for ultrafast optics and spectroscopy, by the variation of their unique properties, e.g., entanglement and photon statistics, after interacting with materials. Quantum light possesses unique characteristics that distinguish it from classical light, particularly the phase-space distribution which reflects its fundamental quantum statistics and the quantum control protocol that may take advantage of noise reduction. This Review will focus on spectroscopic applications using entangled photons and squeezed light, in conjunction with quantum coherent control. We provide a brief introduction to the generation of the entangled and squeezed light, discussing their fundamental properties and connections to the control protocol that may enhance spectroscopic techniques. A microscopic theory for the spectroscopy and corresponding signals induced by certain transition processes is developed. Nonlinear optical signals induced by entangled photons for the coherent anti-Stokes Raman spectra (CARS) and the stimulated Raman spectra (SRS) are investigated. We further extend our efforts to the transient absorption process that enables real-time monitoring of the exciton transfer in the transition metal dichalcogenides (TMDs), namely, using the WS 2 monolayer. This series of works on nonlinear optical spectroscopy using quantum light explicitly demonstrates the quantum supremacy in ultrafast spectroscopy through jointly enhancing the time and energy scales beyond the classical bound.

Progress in Quantum ElectronicsJan 28, 20260 citations

Entangled Photons Enabled Ultrafast Stimulated Raman Spectroscopy for Molecular Dynamics

Zhedong Zhang, Jiahao Fan, Z. Y. Ou

Abstract Quantum entanglement has emerged as a great resource for studying the interactions between molecules and radiation. We propose a new scheme of stimulated Raman scattering with entangled photons. A quantum ultrafast Raman spectroscopy is developed for condensed-phase molecules, to monitor the exciton populations and coherences. Analytic results are obtained, showing an entanglement-enabled time-frequency scale not attainable by classical light. The Raman signal presents an unprecedented selectivity of molecular correlation functions, as a result of the Hong-Ou-Mandel interference. Our work suggests a new paradigm of using an unconventional interferometer as part of spectroscopy, with the potential to unveil advanced information about complex materials.

Oct 26, 20230 citations