Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap

TL;DR

This paper demonstrates sub-milliKelvin precision in measuring the thermal motion of a single Doppler-cooled ion in a Paul trap, using spatial thermometry based on the ion's position distribution.

Contribution

It introduces a high-precision spatial thermometry method for ions in a trap, enabling detailed investigation of Doppler cooling limits and trap potential effects.

Findings

Achieved sub-milliKelvin temperature measurements.

Calibrated imaging system's point spread function with thermal spread.

Analyzed laser detuning effects on Doppler temperature.

Abstract

We report on observations of thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-milliKelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.