Doppler Cooled Ions in a Compact, Reconfigurable Penning Trap

TL;DR

This paper presents a compact, reconfigurable Penning trap using permanent magnets, demonstrating Doppler laser cooling of ions and enabling low-cost, portable cold ion experiments with high magnetic field uniformity.

Contribution

The first demonstration of Doppler laser cooling in a permanent magnet Penning trap with in situ magnetic field optimization.

Findings

Successful Doppler cooling of $^{40}$Ca$^+$ ions at 0.65 T

Observation of crystalline ion arrays

Trap frequencies match magnetic field measurements

Abstract

We report the design and experimental demonstration of a compact, reconfigurable Penning ion trap constructed with rare-earth permanent magnets placed outside of a trap vacuum enclosure. We describe the first observation of Doppler laser cooling of ions in a permanent magnet Penning trap. We detail a method for quantifying and optimizing the trap magnetic field uniformity in situ using a thermal beam of neutral $^{40}$Ca precursor atoms. Doppler laser cooling of $^{40}$Ca$^+$ is carried out at 0.65~T, and side-view images of trapped ion fluorescence show crystalline order for both two- and three-dimensional arrays. Measured $^{40}$Ca$^+$ trap frequencies confirm the magnetic field characterization with neutral $^{40}$Ca. The compact trap described here enables a variety of cold ion experiments with low size, weight, power, and cost requirements relative to traditional electromagnet-based Penning traps.