Abstract
Vibrational strong coupling has emerged as a promising route for manipulating the reactivity of molecules inside infrared cavities. We develop a full-quantum methodology to study the unitary dynamics of a single anharmonic vibrational mode interacting with a quantized infrared cavity field. By comparing multi-configurational time-dependent Hartree simulations for an intracavity Morse oscillator with an equivalent formulation of the problem in Hilbert space, we describe for the first time the essential role of permanent dipole moments in the femtosecond dynamics of vibrational polariton wavepackets. We classify molecules into three general families according to the shape of their electric dipole function de(q) along the vibrational mode coordinate q. For polar species with a positive slope of the dipole function at equilibrium, an initial diabatic light-matter product state without vibrational or cavity excitations evolves into a polariton wavepacket with a large number of intracavity photons for interaction strengths at the conventional onset of ultrastrong coupling. This buildup of the cavity photon amplitude is accompanied by an effective lengthening of the vibrational mode that is comparable with a laser-induced vibrational excitation in free space. In contrast, polar molecules with a negative slope of the dipole function experience an effective mode shortening, under equivalent coupling conditions. We validate our predictions using realistic ab initio ground state potentials and dipole functions for HF and CO2 molecules. We also propose a non-adiabatic state preparation scheme to generate vibrational polaritons with molecules near infrared nanoantennas for the spontaneous radiation of infrared quantum light.
Highlights
Recent experimental demonstrations of strong and ultrastrong light–matter interaction with molecules and molecular materials in infrared cavities1–18 have stimulated intense theoretical efforts for understanding the microscopic properties of hybrid photonvibration states from a quantum mechanical perspective.19 Motivated by pioneering measurements in liquid-phase Fabry–Perot cavities,5,17,20 theoretical studies have suggested several potential mechanisms that enable the modification of chemical reactivity in the ground electronic state under conditions of vibrational strong coupling.21–23 Another theoretical focus is the study of linear and nonlinear spectroscopic signals of infrared cavities under strong coupling.19,24–27Vibrational polaritons are the hybrid light–matter states that emerge in infrared cavities under strong coupling.28 Several models with varying degrees of complexity have been used to study these systems
This approach corresponds to the Tavis–Cummings model of cavity quantum electrodynamics (QED),30 which implies the rotating-wave approximation for light– matter coupling
We have shown that the resonant interaction of an individual molecular vibration with a quantized cavity field can have very different physical observable consequences depending on the dipolar properties of the molecular electron density
Summary
Recent experimental demonstrations of strong and ultrastrong light–matter interaction with molecules and molecular materials in infrared cavities have stimulated intense theoretical efforts for understanding the microscopic properties of hybrid photonvibration states from a quantum mechanical perspective. Motivated by pioneering measurements in liquid-phase Fabry–Perot cavities, theoretical studies have suggested several potential mechanisms that enable the modification of chemical reactivity in the ground electronic state under conditions of vibrational strong coupling. Another theoretical focus is the study of linear and nonlinear spectroscopic signals of infrared cavities under strong coupling.19,24–27Vibrational polaritons are the hybrid light–matter states that emerge in infrared cavities under strong coupling. Several models with varying degrees of complexity have been used to study these systems. Motivated by pioneering measurements in liquid-phase Fabry–Perot cavities, theoretical studies have suggested several potential mechanisms that enable the modification of chemical reactivity in the ground electronic state under conditions of vibrational strong coupling.. Motivated by pioneering measurements in liquid-phase Fabry–Perot cavities, theoretical studies have suggested several potential mechanisms that enable the modification of chemical reactivity in the ground electronic state under conditions of vibrational strong coupling.21–23 Another theoretical focus is the study of linear and nonlinear spectroscopic signals of infrared cavities under strong coupling.. The vibrational qubits were scitation.org/journal/jcp simultaneously coupled to a quantized harmonic oscillator describing a single-mode cavity field. This approach corresponds to the Tavis–Cummings model of cavity quantum electrodynamics (QED), which implies the rotating-wave approximation for light– matter coupling. Light–matter coupling was extended to include the counter-rotating and selfenergy terms that are commonly taken into account under conditions of ultrastrong coupling, broadly defined as the regime in which the light–matter interaction energy is comparable with the vibrational and cavity frequencies
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