Quantum Ghost Spectroscopy Reveals Hidden Coherence in Molecular Aggregates
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Updated: Nov 6, 2026

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Mingran Zhang1, Yihe Xu1, Vladislav V Yakovlev2,3
1Department of Physics, City University of Hong Kong, Kowloon999077, Hong Kong SAR.
Abstract:
Ultrafast spectroscopy of complex molecules has been achieved under light-matter coupling by the use of laser pulses and single photons. Yet, the excited-state dynamics essential to photochemistry is suffering from the convolution of multiple relaxation pathways and limited resolution in nonlinear signal, which still remain challenging. To address these, we develop time-resolved quantum ghost spectroscopy (tr-QGS) with entangled light, which enables a background-free detection of excited-state emission while offering precise control over temporal resolution. We apply this approach to perylene bisimide (PBI-1) trimers 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 captures electronic coherence oscillating at 0.6 eV for ∼50 fs, a signature of nonadiabatic coupling that was obscured in time-resolved measurements. Moreover, we observe a direct transfer from electronic to vibrational coherence at 200 fs, providing real-time visualization of vibronic relaxation pathways. Photon entanglement eliminates background noise and ground-state bleaching artifacts, which plague time-resolved 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 effects in chemistry with unprecedented precision.
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