In attempts to unify all fundamental forces in a single quantum consistent theory it has been suggested that Lorentz symmetry is violated. We have investigated the principle of local Lorentz invariance in a single trapped Yb+ ion by comparing spatially oriented atomic orbitals. The highly relativistic 2F7/2 Zeeman manifold has been shown to be exceptionally sensitive to Lorentz violation. We have implemented a highly robust composite pulse rf sequence for accurate Ramsey spectroscopy in the eight-level system with second long interrogation time. Hereby, we exploit the most sensitive mj= ±7/2 sublevels and the exceptionally long lifetime of the 2F7/2 state (~1.6 year). With our novel scheme we reach the highest sensitivity to Lorentz violation in the electron-photon sector to date. We search for Lorentz violation with signals at the rotation period of Earth (23.9345 h) and its second harmonic. A 5-week long measurement campaign revealed no significant effect stemming from Lorentz violation, but we could set new bounds at world-record accuracy. A further improvement in sensitivity can be made in the future by scaling to multiple ions in a Coulomb crystal.
A PTB press release can be found here.