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Q: Fachverband Quantenoptik und Photonik

Q 64: Poster – Ultra-cold atoms, ions and BEC (joint session A/Q)

Q 64.33: Poster

Thursday, March 5, 2026, 17:00–19:00, Philo 1. OG

Optimizing pulsed resolved sideband cooling outside the Lamb–Dicke regime — •Elwin A. Dijck, Sebastian Davidson, Ruben B. Henninger, Shreya Rao Kodancha, Devanarayanan Rajeeb Kumar, Stepan Kokh, Vera M. Schäfer, Thomas Pfeifer, and José R. Crespo-López Urrutia — Max-Planck-Institut für Kernphysik, Heidelberg

Cooling ions to the motional ground state of their harmonic trapping potential minimizes Doppler shifts and enables techniques like quantum logic spectroscopy. Ion motion modulating a narrow transition produces resolved sidebands that allow changing the motional state in controlled steps beyond the Doppler limit. In the Lamb–Dicke regime, the modulation is small: repeated excitation of the first-order red sideband and repumping successively lowers the phonon number to zero.

Limited trap depth may prevent reaching this regime and presents challenges in sideband cooling: the Doppler limit now corresponds to a larger initial phonon number, and absorption and emission during repumping cause significant heating. However, the larger modulation index also produces higher order sidebands in the spectrum, allowing removal of more than one phonon per step.

Simulating the probability distribution over Fock states for one and two-ion crystals during the cooling process, we investigate optimized pulse sequences for different combinations of Lamb–Dicke factors and ion species, considering in particular mixed-species crystals comprising a Be⁺ ion and a highly charged ion.

Keywords: Resolved sideband cooling; Laser cooling; Ion trapping; Highly charged ions