Precision measurement of the 5 2S1/2 - 4 2D5/2 quadrupole transition isotope shift between 88Sr+ and 86Sr+

TL;DR

This study reports the first high-precision measurement and calculation of the isotope shift in the 5 2S1/2 - 4 2D5/2 transition of Sr+ ions, highlighting discrepancies and guiding future theoretical improvements.

Contribution

It provides the first precise experimental and theoretical comparison of isotope shifts in Sr+ ions, testing ab-initio calculation methods against high-resolution spectroscopy data.

Findings

Measured isotope shift: 570.281(4) MHz

Calculated isotope shift: 457(28) MHz

Discrepancy suggests underestimation of specific mass shift in calculations

Abstract

We have measured the isotope shift of the narrow quadrupole-allowed 5 2S1/2 - 4 2D5/2 transition in 86Sr+ relative to the most abundant isotope 88Sr+. This was accomplished using high-resolution laser spectroscopy of individual trapped ions, and the measured shift is Delta-nu_meas^(88,86) = 570.281(4) MHz. We have also tested a recently developed and successful method for ab-initio calculation of isotope shifts in alkali-like atomic systems against this measurement, and our initial result of Delta-nu_calc^(88,86) = 457(28) MHz is also presented. To our knowledge, this is the first high precision measurement and calculation of that isotope shift. While the measurement and the calculation are in broad agreement, there is a clear discrepancy between them, and we believe that the specific mass shift was underestimated in our calculation. Our measurement provides a stringent test for further refinements of theoretical isotope shift calculation methods for atomic systems with a single valence electron.