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

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.