Radio-frequency sideband cooling and sympathetic cooling of trapped ions in a static magnetic field gradient

TL;DR

This paper demonstrates a simple RF sideband cooling technique for trapped ions in a magnetic field gradient, achieving near-ground state cooling and sympathetic cooling of ion crystals, with results matching theoretical predictions.

Contribution

The authors introduce and experimentally validate a novel RF sideband cooling method applicable to ions in a static magnetic field gradient, including sympathetic cooling of multi-ion systems.

Findings

Achieved ground state cooling of a single ion with $ abla n = 0.30(12)$

Extended RF sideband cooling to two ions, reaching $ abla n = 1.1(7)$ in the COM mode

First demonstration of sympathetic RF sideband cooling of identical ion isotopes

Abstract

We report a detailed investigation on near-ground state cooling of one and two trapped atomic ions. We introduce a simple sideband cooling method for confined atoms and ions, using RF radiation applied to bare ionic states in a static magnetic field gradient, and demonstrate its application to ions confined at secular trap frequencies, $\omega_z \approx 2\pi\times 117 $kHz. For a single \ybplus ion, the sideband cooling cycle reduces the average phonon number, $\left\langle\,n\,\right\rangle$ from the Doppler limit to $\left\langle\,n\,\right\rangle =$ 0.30(12). This is in agreement with the theoretically estimated lowest achievable phonon number in this experiment. We extend this method of RF sideband cooling to a system of two \ybplus ions, resulting in a phonon number of $\left\langle\,n\,\right\rangle =$ 1.1(7) in the center-of-mass mode. Furthermore, we demonstrate the first realisation of sympathetic RF sideband cooling of an ion crystal consisting of two individually addressable identical isotopes of the same species.