Probe field ellipticity-induced shift in an atomic clock

TL;DR

This paper analyzes how residual ellipticity in probe laser polarization causes frequency shifts in atomic clocks, which can be significant but mitigated using hyper-Ramsey spectroscopy, impacting clock accuracy.

Contribution

It identifies a previously underappreciated probe field ellipticity-induced shift in atomic clocks and demonstrates its reduction via hyper-Ramsey spectroscopy.

Findings

Ellipticity-induced shift can reach 10^{-18} - 10^{-19}

Shift depends on magnetic field orientation and polarization residuals

Hyper-Ramsey spectroscopy significantly reduces the shift

Abstract

We investigate the probe field induced shift for atomic lattice-based and ion-trap clocks, which can be considered as a near resonant ac-Stark shift, connected to the Zeeman structure of atomic levels and their splitting in a dc magnetic field. This shift arises from possible residual ellipticity in the polarization of the probe field and uncertainty in the magnetic field orientation. Such a shift can have an arbitrary sign and, for some experimental conditions, can reach the fractional value of the order of 10$^{-18}$-10$^{-19}$, i.e., it is not negligible. Thus, it should be taken into account in the uncertainty budgets for the modern ultra-precise atomic clocks. In addition, it is shown that when using hyper-Ramsey spectroscopy, this shift can be reduced to a level much lower than $10^{-19}$.