A witness for coherent electronic oscillations in ultrafast spectroscopy

TL;DR

This paper introduces a simple method to identify genuine electronic coherence in ultrafast spectroscopy, helping distinguish it from vibronic effects and resolving debates in photosynthetic systems.

Contribution

The authors propose a straightforward witness based on broadband pump/probe spectra to isolate electronic oscillations, offering a practical alternative to complex quantum process tomography.

Findings

Coherent oscillations in waiting time indicate electronic coherence.

Oscillations in individual 2D spectral peaks may not signify electronic coherence.

The method simplifies analysis of ultrafast spectra in light-harvesting systems.

Abstract

We report a conceptually straightforward witness that isolates coherent electronic oscillations from their vibronic counterparts in nonlinear optical spectra of molecular aggregates: Coherent oscillations as a function of waiting time in broadband pump/broadband probe spectra correspond to coherent electronic oscillations. Oscillations in individual peaks of 2D electronic spectra do not necessarily yield this conclusion. Our witness is simpler to implement than quantum process tomography and potentially resolves a long-standing controversy on the character of oscillations in ultrafast spectra of photosynthetic light harvesting systems.