Long-lived oscillatory incoherent electron dynamics in molecules: trans-polyacetylene oligomers

TL;DR

This study reveals long-lived oscillatory electron dynamics in trans-polyacetylene oligomers, driven by incoherent vibronic interactions, which mimic quantum coherence but are fundamentally incoherent, providing insights into molecular electronic coherence.

Contribution

It demonstrates that long-lived oscillations in electron dynamics are incoherent in nature, challenging the assumption that such patterns indicate quantum coherence in molecules.

Findings

Oscillatory electron exchange persists for tens of picoseconds.

The oscillations are caused by incoherent vibronic interactions.

Long-lived oscillations do not necessarily imply electronic coherence.

Abstract

We identify an intriguing feature of the electron-vibrational dynamics of molecular systems via a computational examination of \emph{trans}-polyacetylene oligomers. Here, via the vibronic interactions, the decay of an electron in the conduction band resonantly excites an electron in the valence band, and vice versa, leading to oscillatory exchange of electronic population between two distinct electronic states that lives for up to tens of picoseconds. The oscillatory structure is reminiscent of beating patterns between quantum states and is strongly suggestive of the presence of long-lived molecular electronic coherence. Significantly, however, a detailed analysis of the electronic coherence properties shows that the oscillatory structure arises from a purely incoherent process. These results were obtained by propagating the coupled dynamics of electronic and vibrational degrees of freedom in a mixed quantum-classical study of the Su-Schrieffer-Heeger Hamiltonian for polyacetylene. The incoherent process is shown to occur between degenerate electronic states with distinct electronic configurations that are indirectly coupled via a third auxiliary state by the vibronic interactions. A discussion of how to construct electronic superposition states in molecules that are truly robust to decoherence is also presented.