# Phase-Resolved Two-Dimensional Infrared Spectroscopy of Solution-Phase Vibrational Polaritons on Gold Antenna Meta-Surfaces

## TL;DR

This paper explores vibrational polaritons using advanced infrared spectroscopy and gold antenna meta-surfaces to understand their quantum properties and behavior.

## Contribution

The study introduces phase-resolved 2DIR spectroscopy to reveal the anharmonic nature and reservoir state coupling of solution-phase vibrational polaritons.

## Key findings

- Phase-resolved 2DIR line shapes show the anharmonic character of vibro-polaritons.
- Coupling with molecular-like reservoir states is revealed through nonlinear spectroscopy.
- Experimental data align with theoretical models, ruling out alternative explanations like inhomogeneous frequency distribution.

## Abstract

Vibrational polaritons are quasiparticles that form when
optically
allowed molecular vibrations strongly couple to photonic resonances
of infrared cavity. Understanding vibro-polariton properties is essential
to harness their potential in fields from synthetic chemistry to quantum
technologies. We studied vibro-polaritons generated with infrared
meta-surfaceshigh-optical-quality arrays of gold microantennas.
Linear and third-order nonlinear two-dimensional infrared spectroscopy
(2DIR) combined with electromagnetic analysis emphasized, on one hand,
the surface-confined character of vibro-polariton waves and their
quantum state nature on the other. Phase-resolved 2DIR line shapes
highlighted the anharmonic character of vibro-polaritons and revealed
coupling with the excitation of molecular-like reservoir states. Experimental
data were qualitatively described by nonlinear response functions
with signal phases obtained from electromagnetic calculations and
anharmonic constants of few wavenumbers. Such agreement allows us
to rule out alternative scenarios like selective signal enhancement
from inhomogeneous distribution of molecular frequencies or signal
amplification by weak coupling to photonic resonances.