Rotating Michelson-Morley experiment based on a dual cavity cryogenic sapphire oscillator

Recent experiments based on cryogenic microwave oscillators have tested the isotropy of the speed of light (Michelson-Morley experiment) at sensitivities of the order of a part in 10/sup 15/, which is a similar sensitivity to other best tests. Further improvements of the accuracy in this type of experiment are not expected due to the already long data set and the systematic error limit. We have constructed a new rotating Michelson-Morley experiment consisting of two cylindrical cryogenic sapphire resonators. The temperature of the dual cavity is controlled at approximately 6 K where the beat frequency between the two oscillators is independent of temperature. By rotating the experiment, an improvement of several orders of magnitude in our sensitivity to light speed anisotropy is expected, as the relevant time variations will now be at a rotation frequency where the frequency stability of the cryogenic oscillators is at its best.