Atomic and nuclear clocks for testing fundamental physics
Ekkehard Peik (PTB Braunschweig)

We use frequency comparisons between highly accurate optical clocks for tests of fundamental principles. In particular, the 171Yb+ optical clock based on an electric octupole transition between the S-ground state and the lowest excited F-level with a radiative lifetime of 1.58 years provides a favorable combination of low systematic uncertainty and high sensitivity to relativistic effects and potentially new physics. Using this system we have established improved limits for violations of local position invariance (in space and time), including the presently most stringent limits for temporal variations of the fine structure constant and the electron-proton mass ratio. I will give an outlook on the development of a 229Th nuclear optical clock that will open new perspectives for fundamental tests in the domain of nuclear physics.