Research

Average isomerization probability for a specific value of cavity-system coupling strength as a function of the cavity frequency. The quantum (in blue, circles) and the corresponding classical (in red, squares) results are shown. The dotted vertical line indicates the cavity frequency being resonant with the Harmonic frequency of the reactive mode and the solid vertical line indicates the 0 → 1 fundamental transition frequency of the reactive mode. Note that maximum suppression of <P_{iso}> happens near the Harmonic frequency of the reactive mode with very good classical-quantum correspondence.

a) Average fast Lyapunov indicator (FLI) values corresponding to the initial quantum state in Fig. 1(a). The classical trajectories are propagated to a final time of T = 1000fs. The inset shows FLI versus time behavior for example chaotic (gray, arrow) and regular (shaded region, colors) trajectories. Note that the FLI values can distinguish between chaotic and regular trajectories by t ∼ 375 fs (indicated by a vertical dashed line). (b) Distribution of FLI values for two different choices of the cavity frequency ωc = 945.6 cm−1 (magenta) and 1229 cm−1 (blue).

Polariton Chemistry

Isomerization in an Optical Cavity: Phase Space Perspective on Dynamical Localization

In recent years vibrational strong coupling has raised our hope of achieving the “holy grail” of mode-specific chemistry. Pioneering experiments[1] by Ebbesen and co-workers have demonstrated that coupling of the quantum light in an optical cavity to molecular vibrations can significantly suppress or enhance chemical reaction rates in interesting ways. However, the precise mechanism of how this coupling to the cavity mode alters the reactivity is still under debate. Several crucial insights have emerged recently that the changes in the nature of molecule-cavity vibrational energy flow play a significant role in influencing reaction dynamics[2,3,4]. In the present work, we study both quantum and classical dynamics of a model isomerization reaction - the inversion of ammonia along the umbrella mode, in the presence of a single cavity mode. Our results[5] show that the cavity has a significant effect on the isomerization reaction. Depending upon the initial vibropolaritonic wavepacket, isomerization probability can get suppressed or enhanced compared to their off-cavity value. Furthermore, we show that with varying frequency cavity mode can dynamically localize the initial vibropolaritonic wavepacket in the reactant well. Interestingly, classical dynamics can also capture this “dynamical localization” phenomenon around the same cavity frequency range. We argue that this effect can be rationalized in terms of large scale changes of the structures in the classical phase space. Moreover, with varying cavity frequency the emergence of regularity in the phase space undergoes a “chaos-order-chaos” type of behavior which results in the nontrivial modulations of the isomerization probability.

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Classical Poincare surface of sections for varying cavity frequencies at fixed coupling η = 0.06. (Top row) System (q, p) phase space corresponds to the reactant well with the sectioning condition xc = minimum xc and pc > 0. (Bottom row) Photon (xc, pc) phase space with sectioning condition q = ̄q− = −0.75 au and p > 0. The purple arrow indicates the appearance of a 1:1 cavity-system nonlinear resonance and the blue arrow shows the appearance of regular trajectories undergoing transition from the reactant well to the product well. The cavity frequencies and the corresponding average energies at which the sections are computed are indicated.

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