Vibrational Coupling of Water from Weak to Ultrastrong Coupling Regime via Cavity Mode Tuning

Abstract

Vibrational strong coupling is an emerging method for modulation of ground-state molecular properties. Spectroscopic information about the vibrational coupling state is essential for determination of the physicochemical properties of molecules coupled to vacuum electromagnetic fields. However, a systematic study of the effect of the cavity mode with respect to the coupling strength is still required. Here, we show the effect of the cavity mode on the vibrational coupling behavior of water molecules when tuned from a weak coupling regime to an ultrastrong coupling regime. The cavity thickness was controlled mechanically for modulation of the cavity mode frequency. The concentration-dependent Rabi splitting behavior is a critical for determination of the coupling behavior of water molecules to vacuum fields. We also showed the advantages of use of thinner cells for clear spectroscopic investigation of the coupling states and the possibility of modulation of the hydration environment based on cavity control. In addition, we provide the fundamental cavity mode-dependent structure relationship for the controlled molecular properties within a wide coupling strength regime.

Inherent Promotion of Ionic Conductivity via Collective Vibrational Strong Coupling of Water with the Vacuum Electromagnetic Field

“…This was likely because of the lower coupling strength of the polariton state due to the lower oscillator strength. 33 Moreover, the unique coupling effect between the OH vibration and the cavity was confirmed based on a control experiment using a deuterated 0.01 M DClO 4 /D 2 O solution. In this case, the resonance conditions required a cavity length of 1.5 μm to achieve vibrational strong coupling (Figure 3c,d) because of the different vibrational frequencies (ω st,OH = 3400 cm −1 , ω st,OD = 2500 cm −1 ).…”

“…The homogeneity of the cavity thickness was verified based on the observed Newton rings by eye, which were generated from the structural interference of the cavity within a few hundred of nanometers. 33 The modulated response was influenced by the cavity thickness, and the microscopic surface roughness of the CaF 2 window likely contributed to this dependence. The cavity modes were determined based on the fringe in the peak-to-peak separation of cavity modes (typical spectroscopic properties are shown in Figure S2).…”

“…Water is typically characterized according to representative physicochemical properties, such as chemical reactivity, hydration, and thermodynamic properties. − Even under static conditions, protons move along a hydrogen bond network via proton transfer and reorientations of water molecules (Figure b); this behavior is known as the Grotthuss mechanism. − Vibrational strong coupling is often exploited to modify the ground-state reactivity and solvation of water molecules. − Accordingly, the proton-transfer process and reorientation of water molecules in the Grotthuss mechanism can be perturbed by vibrational strong coupling. However, to our knowledge, there have been no reports describing how vibrational strong coupling can influence the fundamental ionic transport properties of aqueous electrolyte solutions.…”

Quantum Simulations of Vibrational Strong Coupling via Path Integrals

“…Here, to investigate the potential impact of nuclear and photonic quantum effects, we report the first quantum CavMD simulation of liquid water under VSC by path-integral techniques. − While path-integral techniques have been used to study strong light–matter interactions, ,, a realistic simulation in the collective regime has not yet been reported. Because of the importance of liquid water, understanding how nuclear and photonic quantum effects alter the VSC dynamics ,,− is fundamentally intriguing. Apart from this fundamental motivation, performing a quantum simulation is also needed for a better understanding of the gap between recent VSC experiments and theory.…”

Quantum Simulations of Vibrational Strong Coupling via Path Integrals

“…[34][35][36][37] While path-integral techniques have been used to study strong lightmatter interactions, 22,38,39 a realistic simulation in the collective regime has not yet been reported. Due to the importance of liquid water, understanding how nuclear and photonic quantum effects alter the VSC dynamics 17, [40][41][42][43] is fundamentally intriguing. Apart from this fundamental motivation, performing a quantum simulation is also needed for a better understanding of the gap between recent VSC experiments and theory.…”