Infrared absorption spectroscopy of a single polyatomic molecular ion

TL;DR

This paper demonstrates a nondestructive, high-sensitivity infrared absorption spectroscopy technique on a single polyatomic molecular ion using recoil detection amplified by quantum motion states.

Contribution

It introduces a novel recoil-based detection method for single-molecule infrared absorption spectroscopy, enabling quantum non-demolition measurements of complex molecules.

Findings

Successful detection of single-photon absorption via recoil signals

Characterization of vibrational interactions with femtosecond laser pulses

First single-photon vibrational absorption spectrum of CaOH+ molecular ion

Abstract

Absorption spectroscopy is a fundamental tool for probing molecular structure. However, performing absorption spectroscopy on individual molecules is challenging due to the low signal-to-noise ratio. Here, we report on a nondestructive absorption spectroscopy on a mid-infrared vibrational transition in a single molecular ion that is co-trapped with an atomic ion. The absorption of a single photon is detected via the momentum transfer from the absorbed photon onto the molecule. This recoil signal is amplified using a non-classical state of motion of the two-ion crystal and subsequently read out via the atomic ion. We characterize the recoil detection method and use it to investigate the interaction between femtosecond laser pulses and the O-H stretching vibration in individual CaOH+ molecular ions. Furthermore, we present the single-photon absorption spectrum obtained for the vibrational transition. This method represents a milestone towards quantum non-demolition measurements of complex polyatomic molecules, providing high-fidelity methods for preparation and measurement of the quantum state of a wide range of molecular species.