Absolute Single Ion Thermometry

TL;DR

This paper introduces a precise single-ion thermometry method using velocity-dependent spectral shapes, validated on a single Sr+ ion, achieving sub-100 microkelvin accuracy in temperature measurements without adjustable parameters.

Contribution

The authors develop and experimentally validate a novel absolute thermometry technique for single ions, applicable across all laser-cooled atomic ion species, with high accuracy and simplicity.

Findings

Achieved temperature measurement accuracy within 100 μK at 500 μK.

Validated the method on a single Sr+ ion in a surface RF trap.

Demonstrated the technique's potential for heat transport and thermodynamics studies.

Abstract

We describe and experimentally implement a single-ion local thermometry technique with absolute sensitivity adaptable to all laser-cooled atomic ion species. The technique is based on the velocity-dependent spectral shape of a quasi-dark resonance tailored in a J $\rightarrow$ J transition such that the two driving fields can be derived from the same laser source leading to a negligible relative phase shift. We validated the method and tested its performances in an experiment on a single 88 Sr + ion cooled in a surface radio-frequency trap. We first applied the technique to characterise the heating-rate of the surface trap. We then measured the stationary temperature of the ion as a function of cooling laser detuning in the Doppler regime. The results agree with theoretical calculations, with an absolute error smaller than 100 $\mu$K at 500 $\mu$K, in a temperature range between 0.5 and 3 mK and in the absence of adjustable parameters. This simple-to-implement and reliable method opens the way to fast absolute measurements of single-ion temperatures in future experiments dealing with heat transport in ion chains or thermodynamics at the single-ion level.