Freiburg 2024 – scientific programme

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SYCC: Symposium Controlled Molecular Collisions

SYCC 1: Controlled Molecular Collisions

SYCC 1.2: Invited Talk

Wednesday, March 13, 2024, 11:30–12:00, Paulussaal

Angular momentum of small molecules: quasiparticles and topology — •Mikhail Lemeshko — Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria

I will present our recent findings on small molecules kicked by laser pulses. First, I will describe a technique that allows to probe highly excited molecular states in the presence of an environment, such as superfluid 4He, and a theory based on angulon quasiparticles that describes such states, in good agreement with experiment. Second, I will show how that even the simplest of existing molecules - closed-shell diatomics not interacting with one another - host topological charges when driven by periodic far-off-resonant laser pulses. A periodically kicked molecular rotor can be mapped onto a ``crystalline'' lattice in angular momentum space. This allows to define quasimomenta and the band structure in the Floquet representation, by analogy with the Bloch waves of solid-state physics. We predict the occurrence of Dirac cones with topological charges, protected by reflection and time-reversal symmetry. These Dirac cones -- and the corresponding edge states -- are broadly tunable by adjusting the laser strength and can be observed in present-day experiments by measuring molecular alignment and populations of rotational levels. This paves the way to study controllable topological physics in gas-phase experiments with small molecules as well as to classify dynamical molecular states by their topological invariants. [1] I. Cherepanov et al. Phys. Rev. A 104, L061303 (2021); New J. Phys. 24 075004 (2022) [2] V. Karle et al. Phys. Rev. Lett. 130, 103202 (2023); arXiv:2307.07256 (2023)

Keywords: superfluid helium droplets; molecular alignment; kicked rotor; topology and geometric phase; molecular rotations