Application of General-order Relativistic Coupled-cluster Theory to Estimate Electric-field Response Clock Properties of Ca$^+$ and Yb$^+$

TL;DR

This paper employs advanced relativistic coupled-cluster theory to accurately compute electric-field response properties of Ca$^+$ and Yb$^+$ ions, aiding in the precision of optical clock systematic uncertainty estimates.

Contribution

It introduces a comprehensive relativistic coupled-cluster approach for calculating electric response properties of clock ions, emphasizing the importance of triple excitations for accuracy.

Findings

Triple excitations significantly improve property calculations.

Calculated properties closely match experimental data.

Method enhances uncertainty estimation in optical clocks.

Abstract

Accurate calculations of electric dipole polarizabilities ($\alpha_d$), quadrupole moments ($\Theta$), and quadrupole polarizabilities ($\alpha_q$) for the clock states of the singly charged calcium (Ca$^+$) and ytterbium (Yb$^+$) ions are presented using the general-order relativistic coupled-cluster (RCC) theory. Precise knowledge of these quantities is immensely useful for estimating uncertainties caused by major systematic effects such as the linear and quadratic Stark shifts and black-body radiation shifts in the optical Ca$^+$ and Yb$^+$ clocks. A finite-field approach is adopted for estimating these quantities, in which the first-order and second-order energy level shifts are analyzed by varying strengths of externally applied electric field and field-gradient. To achieve high-accuracy results in the heavier Yb$^+$ ion, we first calculate these properties in a relatively lighter clock candidate, Ca$^+$, which involves similar clock states. From these analyses, we learned that electron correlation effects arising from triple excitations in the RCC theory contribute significantly to the above properties, and are decisive factors in bringing the calculated values closer to the experimental results.