Ultrafast Transmission Modulation and Recovery via Vibrational Strong Coupling

Abstract

Strong coupling between vibrational modes and cavity optical modes leads to the formation of vibration-cavity polaritons, separated by the vacuum Rabi splitting. The splitting depends on the square root of the concentration of absorbers confined in the cavity, which has important implications on the response of the coupled system after ultrafast infrared excitation. In this work, we report on solutions of W(CO) in hexane with a concentration chosen to access a regime that borders on weak coupling. Under these conditions, large fractions of the W(CO) oscillators can be excited, and the anharmonicity of the molecules leads to a commensurate reduction in the Rabi splitting. We report excitation fractions > 0.4, depending on excitation pulse intensity, and show drastic increases in transmission that can be modulated on the picosecond time scale. In comparison to previous experiments, the transient spectra that we observe are much simpler because excited-state transitions lie outside of the transmission spectrum of the cavity, thereby contributing only weakly to the spectra. We find that the Rabi splitting recovers with the characteristic vibrational relaxation lifetime and anisotropy decay of uncoupled W(CO), implying that polaritons are not directly involved in the relaxation we observe after the first few ps. The results help corroborate the model that we proposed to describe the results at higher concentrations and show that the ground-state bleach of cavity-coupled molecules has a broad, multisigned spectral response.

Resonant catalysis of thermally activated chemical reactions with vibrational polaritons

“…It is important to highlight that the VSC in these samples is the consequence of an ensemble effect: each cavity mode (that is resonant with the polarization of the material) coherently couples to a large number of molecules. This coupling leads to two polaritonic modes and a macroscopic set of quasi-degenerate dark (subradiant) modes that, to a good approximation, should feature chemical dynamics that is indistinguishable from that of the bare molecular modes [16]. This picture could potentially change as a consequence of ultrastrong coupling effects; however, these effects should not be significant for modest Rabi splittings as those observed in the experiments [12][13][14][15].…”

“…It is important to highlight that the VSC in these samples is the consequence of an ensemble effect: each cavity mode (that is resonant with the polarization of the material) coherently couples to a large number of molecules. This coupling leads to two polaritonic modes and a macroscopic set of quasi-degenerate dark (subradiant) modes that, to a good approximation, should feature chemical dynamics that is indistinguishable from that of the bare molecular modes [16]. This picture could potentially change as a consequence of ultrastrong coupling effects; however, these effects should not be significant for modest Rabi splittings as those observed in the experiments [12][13][14][15].From the population of vibrationally excited states at thermal equilibrium, a tiny fraction would be allocated to the polariton modes, with the overwhelming majority residing in the dark-state reservoir [17][18][19][20], unless the temperature is low enough for the lower polariton to overtake the predominant population second to that of the ground * joelyuen@ucsd.edu FIG.…”

Molecular polaritons for controlling chemistry with quantum optics

“…Fabry-Perot cavities [43,55,153], and also cavity-controlled steady-state [38-40, 42, 44, 46, 47, 49, 53, 152, 190] and ultrafast [51,52,54,56,191,192] vibrational spectroscopy.…”

“…In recent years, several experimental groups have used a diverse set of photonic structures to establish the possibility of manipulating intrinsic properties of molecules and molecular materials under conditions of strong and ultrastrong light-matter coupling with a confined electromagnetic vacuum in the optical [28][29][30][31][32][33][34][35][36][37] and infrared [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] regimes. This growing body of experimental results have positioned molecular cavity systems as novel implementations of cavity QED that complement other physical platforms with atomic gases [57], quantum dots [58], quantum wells [59], or superconducting circuits [60].…”

Electron transfer in confined electromagnetic fields

“…electronic states may be affected by coupling to the radiation field in cavities that support infrared photon modes57,[59][60][61][62][63][64][65][66] . Similar cavity modes can be used to affect exciton motion by bridging excitonic energy gaps as in Refs.24-32.…”