Efficient sympathetic cooling in mixed barium and ytterbium ion chains

TL;DR

This paper investigates the efficiency of sympathetic cooling in mixed barium-ytterbium ion chains within a linear RF trap, demonstrating optimal cooling at a specific trap aspect ratio through experimental measurements of ion motion.

Contribution

It provides the first detailed analysis of how trap aspect ratio influences sympathetic cooling efficiency in mixed ion chains, including experimental validation.

Findings

Optimal cooling at aspect ratio ~2.9

Average thermal occupation numbers depend on chain configuration

Sympathetic cooling effectively reduces ion motion across configurations

Abstract

We study sympathetic cooling of the radial ion motion in a linear RF trap in mixed barium-ytterbium chains. Barium ions are Doppler-cooled, while ytterbium ions are cooled through their interaction with cold barium ions. We estimate the efficiency of sympathetic cooling by measuring the average occupation quantum numbers, and thus the temperature, of all radial normal modes of motion in the ion chain. The full set of orderings in a chain of two barium and two ytterbium ions have been probed, and we show that the average thermal occupation numbers for all chain configurations strongly depend on the trap aspect ratio. We demonstrate efficient sympathetic cooling of all radial normal modes for the trap aspect ratio of approximately 2.9.