Quantum Ghost Spectroscopy Reveals Hidden Electronic Coherence in Molecular Aggregates
Ultrafast spectroscopy of molecular systems is fundamentally constrained by the Fourier uncertainty principle: high temporal resolution smears out electronic state signatures, while high spectral resolution obscures dynamic information. Here we overcome this limitation using time-resolved quantum ghost spectroscopy (tr-QGS) with entangled photon pairs, which enables independent control of temporal and spectral scales. We apply this approach to perylene bismide (PBI-1) trimers for energy transfer,by combining a quantum description of light-molecule interaction with time-dependent density matrix renormalization group (TD-DMRG) simulations. This explicitly includes five vibrational modes and nonadiabatic coupling between electronic states. Our simulations reveal that tr-QGS uniquely captures electronic coherence oscillating at 0.7 eV for >50 fs, a signature of nonadiabatic coupling that was obscured in conventional time-resolved fluorescence due to Fourier-limited broadening. Moreover, we observe a direct transfer from electronic to vibrational coherence at 200 fs, providing real-time visualization of vibronic relaxation pathways. The entangled photon correlation enables a sensitivity below the shot-noise limit and suppresses photobleaching artifacts that plague classical measurements. These results establish tr-QGS as a transformative tool for interrogating nonadiabatic dynamics in molecular aggregates, light-harvesting complexes, and photocatalysts, offering a route to reveal quantum coherence in chemistry with unprecedented time-energy precision.