Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 5: Laser Cooling and Trapping

Q 5.3: Talk

Monday, March 2, 2026, 12:15–12:30, P 11

Rotational cooling of trapped molecular ions — •Monika Leibscher, Alexander Blech, and Christiane P. Koch — Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, Germany

Polyatomic molecules are a promising new platform for fundamental physics and quantum information processing due to their rich internal structure. In particular, their rotational degrees of freedom span a large, well-isolated Hilbert space with strong anharmonicities, enabling precise control. Utilizing these features requires trapping and rotational cooling of molecules. We consider polar molecular ions which are co-trapped with atomic ions in a linear Paul trap. Dipole interaction couples molecular rotation to the collective vibration of the particles in the trap [1, 2]. We demonstrate that the complex rotational spectrum of asymmetric top molecules enables strong dipolar coupling that can be utilized for sympathetic sideband cooling of the rotational degrees of freedom [3]. Furthermore, by combining sideband cooling with coherent microwave control [4], we show that it is possible to tailor the rotational state distribution - either depleting arbitrary subspaces or cooling the entire manifold into a single rotational state.

[1] W. C. Campbell, E. R. Hudson, Phys. Rev. Lett. 125, 120501 (2020). [2] M. Leibscher, F. Schmidt-Kaler, Ch. P. Koch, arXiv:2504.00590 (2025). [3] M. Leibscher, Ch. P. Koch, arXiv:2506.20846 (2025). [4] M. Leibscher, E. Pozzoli, C. Perez, M. Schnell, M. Sigalotti, U. Boscain and Ch . P. Koch, Commun. Phys. 5, 110 (2022).

Keywords: rotational cooling; trapped molecular ions; dipole-phonon interaction