In recent years, the rapid development of quantum-entangled light sources and ultrafast-stimulated Raman spectroscopy has opened new avenues for probing and controlling molecular-scale phenomena. These two cutting-edge technologies, when combined, yield an exceptionally powerful analytical tool for studying complex molecular materials.

Stimulated Raman scattering, a nonlinear optical process, offers valuable insights into molecular vibrational properties and interactions. Its unique capability to resolve ultrafast processes, such as electron transfer and energy redistribution, has long been hindered by limitations in time and energy scales. However, by leveraging the quantum advantages of entangled photon sources, researchers from the City University of Hong Kong have now developed a microscopic theory for quantum-enhanced ultrafast stimulated Raman spectroscopy.

The key innovation lies in the use of quantum-correlated photon pairs to induce the stimulated Raman scattering process. Entangled photons exhibit non-classical properties, including correlations in time, frequency, and polarization, which can significantly enhance the frequency and temporal resolution of spectroscopic signals. Molecules actively participate in the process, serving as "beam mixers" for the Raman pump and probe fields rather than merely acting as passive beam splitters for light scattering.

This approach enables "high-speed imaging" of ultrafast molecular dynamics with femtosecond-level time resolution. By tuning the parameters of the nonlinear optical process, the researchers can generate entangled photon pairs that meet the energy transfer conditions required for stimulated Raman scattering, effectively coupling to the ultrafast processes within the molecules under study. The following figure shows how to take high-speed imaging of molecules of PBI trimer.

The implications of this work extend beyond the realm of quantum physics and spectroscopy. The advancements in quantum light source generation and spectral analysis methods are expected to drive progress in diverse fields, including optical communication, quantum computing, materials science, chemical reactions, and biomedical research.

As the field of quantum spectroscopy continues to evolve, we anticipate profound breakthroughs in our understanding of molecular-scale phenomena and the development of more efficient and stable quantum technologies. This research provides a glimpse into the transformative potential of harnessing quantum effects for molecular dynamics investigations.

This work has been published in Light: Science & Application
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