Disorder-induced non-Gaussian states in large ensembles of cavity-coupled molecules

TL;DR

This study shows that disorder in cavity-coupled molecular ensembles induces non-Gaussian vibrational states, which are robust and cannot be captured by classical or semiclassical models, emphasizing quantum effects in polaritonic chemistry.

Contribution

It demonstrates the emergence of non-Gaussian vibrational states due to disorder in a collective cavity-molecule system using exact quantum simulations.

Findings

Disorder causes non-Gaussian vibrational states at the single-molecule level.

Quantum effects are significant and classical approximations fail to capture non-Gaussianity.

Non-Gaussian states persist in larger ensembles, challenging thermal state descriptions.

Abstract

We analyze vibrational dynamics in a toy model for polaritonic chemistry under collective electronic strong coupling. In a Holstein-Tavis-Cummings model, incoherently excited by a photon, we show that disorder leads to non-Gaussian states of vibrational modes on short time scales at the single-molecule level. Using exact matrix product state simulations, we demonstrate that this effect can remain robust for larger molecule numbers, implying that nuclear wave packets cannot be effectively described by thermal states. Furthermore, we compare simulations of the exact quantum dynamics with semiclassical approximations. We find that the Ehrenfest approximation can only well reproduce ensemble-averaged observables for very large system sizes. Also simulations in the truncated Wigner approximation fail to capture the non-Gaussian effects. Our work highlights the importance of disorder and genuine quantum effects in cavity-modified nuclear dynamics in polaritonic chemistry.