We present a powerful formalism, disordered collective dynamics using truncated equations (d-CUT-E), to simulate the ultrafast quantum dynamics of molecular polaritons in the collective strong coupling regime, where a disordered ensemble of $N\gg {10}^6$ molecules couples to a cavity mode. Notably, we can capture this dynamics with a cavity hosting a single effective molecule with $\sim N_{\mathrm{bins}}$ electronic states, where $N_{\mathrm{bins}}\ll N$ is the number of bins discretizing the disorder distribution. Using d-CUT-E we conclude that strong coupling, as evaluated from linear optical spectra, can be a poor proxy for polariton chemistry. For highly disordered ensembles, total reaction yield upon broadband excitation is identical to that outside of the cavity, while narrowband excitation produces distinct reaction yields solely due to differences in the initial states prepared prior to the reaction.

• Received 10 August 2023
• Revised 6 December 2023
• Accepted 1 February 2024

DOI:https://doi.org/10.1103/PhysRevResearch.6.013222

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society