A robust method to reach the motional quantum regime of (anti-)protons in cryogenic multi-Penning traps

TL;DR

This paper proposes a frequency-sweeping cooling scheme for sympathetic laser cooling of (anti-)protons in cryogenic Penning traps, enabling efficient cooling from cryogenic temperatures to the quantum motional regime, overcoming anharmonicity challenges.

Contribution

It introduces a novel frequency-sweeping cooling method that achieves quantum regime cooling of ions in Penning traps, applicable to laser-inaccessible species.

Findings

Cooling scheme effectively reaches quantum motional regime

Frequency sweep mitigates anharmonicity effects

Applicable to various ion species in cryogenic traps

Abstract

Sympathetic laser cooling is a key concept in precision spectroscopy and quantum state control of charged particles. Significant challenges arise in the metrologically relevant case where the effective interaction between the particles is weak and the particle to be cooled exhibits significant initial motional energy. Here we specifically address the most generally applicable case where the laser-cooled ion and the particle of interest are confined to two spatially separate potential wells with equal motional frequency for resonant enhancement of the cooling dynamics. We analyze the latter through numerical simulations and find that anharmonicities of the potential wells can prevent maintaining the resonance condition throughout the cooling process and thus inhibit a significant reduction in motional energy. We propose a cooling scheme that sweeps the trapping frequency of the potential wells. We show that this scheme enables efficient cooling from cryogenic temperatures all the way to the quantum regime of motion. As a specific application scenario, we analyze the sympathetic cooling of (anti-)protons into the quantum regime of motion for quantum-logic-spectroscopy-based tests of CPT invariance at the quantum limit in Penning traps. Nevertheless, our results and cooling strategies are generally applicable to other laser-inaccessible ion species.