Kai C. Grensemann | Searcharxiv

arXiv2025

Precision spectroscopy in Yb+ ions

We report on our progress on multi-ion spectroscopy with Yb+ ions. We first characterized the spatial homogeneity of the magnetic- and the rf-field. Subsequently, to equalize the immense AC Stark shifts of the individual ions in a Coulomb crystal, we utilize a holographic phase plate to convert the Gaussian beam into a flat-top shape. These efforts enable us to excite an 8-ion crystal (172Yb+) on the highly forbidden electric octupole transition. Using 173Yb+ with reduced AC Stark shift, the same beam profile could support the multi-ion operation of 20 ions. This paves the way for future multi-ion optical clocks.

physics.atom-ph↗

arXiv2024

Improved bounds on Lorentz violation from composite-pulse Ramsey spectroscopy in a trapped ion

In attempts to unify the four known fundamental forces in a single quantum-consistent theory, it is suggested that Lorentz symmetry may be broken at the Planck scale. Here we search for Lorentz violation at the low-energy limit by comparing orthogonally oriented atomic orbitals in a Michelson-Morley-type experiment. We apply a robust radiofrequency composite pulse sequence in the $^2F_{7/2}$ manifold of an Yb$^+$ ion, extending the coherence time from 200 $μ$s to more than 1 s. In this manner, we fully exploit the high intrinsic susceptibility of the $^2F_{7/2}$ state and take advantage of its exceptionally long lifetime. We match the stability of the previous best Lorentz symmetry test nearly an order of magnitude faster and improve the constraints on the symmetry breaking coefficients to the 10$^{-21}$ level. These results represent the most stringent test of this type of Lorentz violation. The demonstrated method can be further extended to ion Coulomb crystals.

physics.atom-ph↗