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arXiv · 2511.19687

Infrared absorption spectroscopy of a single polyatomic molecular ion

Zhenlin Wu·Tim Duka·Mariano Isaza-Monsalve·Miriam Kautzky·Vojtěch Švarc·Andrea Turci·René Nardi·Marcin Gronowski·Michał Tomza·Brandon J. Furey·Philipp Schindler
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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.

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Zhenlin Wu, Tim Duka, Mariano Isaza-Monsalve, Miriam Kautzky, Vojtěch Švarc, Andrea Turci, René Nardi, Marcin Gronowski, Michał Tomza, Brandon J. Furey, Philipp Schindler. 2026-05-29. Infrared absorption spectroscopy of a single polyatomic molecular ion. https://arxiv.org/abs/2511.19687

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