New test of the isotropy of space using cryogenic optical resonators

Summary form only given. The special theory of relativity (SR) and the principle of Lorentz covariance lie at the very foundation of today´s physics. An experimental verification of the theory is therefore of great interest and is currently pursued by new ultra-high precision optical experiments, both space-based (SUMO, OPTIS, ...) and terrestrial. Examples for such tests are Michelson-Morley (MM) experiments, establishing the isotropy of the speed of light c(/spl theta/), and Kennedy-Thorndike (KT) experiments, testing the independence of c(/spl nu/) from the velocity /spl nu/ of the observer. Both KT and MM tests can be performed using cryogenic optical resonators (COREs), which provide a unique combination of extremely low thermal expansion and no observable aging effects. Here, we present a MM experiment using existing COREs in a new configuration. After short operation (/spl sim/350 h of data), it already yields a 3-fold improved accuracy compared with the best previous experiment. An improvement by one order of magnitude is aimed for. For our MM experiment, we compare the frequencies /spl nu//sub 1/ and /spl nu//sub 2/ of two CORE-stabilized lasers at 1064 nm in a beat measurement.