Precision isotope shift measurements in Ca$^+$ using highly sensitive detection schemes

TL;DR

This paper introduces a highly sensitive optical spectroscopy method using double-shelving to measure isotope shifts and transition frequencies in trapped calcium ions with unprecedented precision, advancing atomic and nuclear physics research.

Contribution

The authors develop and demonstrate a novel double-shelving technique for high-precision spectroscopy of single trapped ions with non-closed transitions, enabling accurate isotope shift measurements.

Findings

First high-precision absolute frequency measurement of Ca$^+$ transition.

Determination of isotope shifts for multiple calcium isotopes.

Extraction of nuclear charge radius changes and improved shift constants.

Abstract

We demonstrate an efficient high-precision optical spectroscopy technique for single trapped ions with non-closed transitions. In a double-shelving technique, the absorption of a single photon is first amplified to several phonons of a normal motional mode shared with a co-trapped cooling ion of a different species, before being further amplified to thousands of fluorescence photons emitted by the cooling ion using the standard electron shelving technique. We employ this extension of the photon recoil spectroscopy technique to perform the first high precision absolute frequency measurement of the $^{2}$D$_{3/2}$ $\rightarrow$ $^{2}$P$_{1/2}$ transition in $^{40}$Ca$^{+}$, resulting in a transition frequency of $f=346\, 000\, 234\, 867(96)$ kHz. Furthermore, we determine the isotope shift of this transition and the $^{2}$S$_{1/2}$ $\rightarrow$ $^{2}$P$_{1/2}$ transition for $^{42}$Ca$^{+}$, $^{44}$Ca$^{+}$ and $^{48}$Ca$^{+}$ ions relative to $^{40}$Ca$^{+}$ with an accuracy below 100 kHz. Improved field and mass shift constants of these transitions as well as changes in mean square nuclear charge radii are extracted from this high resolution data.