Speaker
Description
Quantum logic spectroscopy (QLS) has been established as a versatile technique for high-precision spectroscopic studies of diatomic molecular ions co-trapped with atomic ions in an ion trap, contributing to fundamental physics research and quantum information applications [1-6]. However, extending this protocol to larger polyatomic molecular species is challenging due to their more complex internal structure and has not yet been demonstrated experimentally. Furthermore, QLS is not directly applicable to studies that use broadband ultra-short laser pulses to investigate fast molecular processes such as intramolecular vibrational redistribution, which plays an important role in chemical and biological processes. Using an adapted version of quantum logic methods, we investigate polyatomic molecular ions by probing their photon-absorption signal. This is achieved by preparing the shared motional mode of the trapped molecular and atomic ions in a non-classical state that is sensitive to the momentum recoil associated with the absorption of a single photon [7]. We demonstrate this scheme by measuring the infrared absorption spectrum corresponding to the O–H stretch mode of a CaOH⁺ ion co-trapped with a Ca⁺ ion using broadband femtosecond laser pulses [8]. The measured spectrum shows good agreement with ab initio theoretical predictions for the transition frequency and oscillator strength. This suggests that the recoil detection method has potential applications in studying more complex polyatomic molecular ions at the single-particle level, such as in the initial identification of transitions, as well as in pump-probe experiments using femtosecond laser pulses that facilitate the investigation of ultrafast intramolecular dynamics [9]. Furthermore, improvements in the signal-to-noise ratio could enable single-shot readout using this technique, combined with spectral shaping this would allow for measurement-based rotational state preparation in polyatomic molecules.
[1] P. O. Schmidt et al., Science 309(5735),749-752 (2005).
[2] F. Wolf et al., Nature 530(7591), 457–460 (2016).
[3] C. W. Chou et al., Nature 545(7653), 203–207 (2017).
[4] M. Sinhal et al., Science 367(6483), 1213–1218 (2020).
[5] D. Holzapfel et al., arXiv:2409.06495 (2024).
[6] L. Qi et al., arXiv:2411.07137 (2024).
[7] C. Hempel et al., Nature Photonics 7, 630–633 (2013)
[8] Z. Wu et al., arXiv:2511.19687 (2025)
[9] P. Schindler, New J. Phys. 21(8), 083025 (2019).
| Academic level | PhD student |
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