A modern Michelson-Morley experiment using ultrastable optical resonators

This talk will describe a modern version of the classic Michelson-Morley experiment testing the isotropy of light propagation and thus the foundations of Special Relativity. The latest experimental setup employs of an assembly of orthogonal ultrastable optical resonators mounted inside a liquid Helium cryostat, which itself is actively rotated using a high performance air-supported turntable. The cavity resonance frequencies are continuously monitored using monolithic Nd:YAG lasers and analyzed for periodic modulations indicating violations of Lorentz-invariance. Compared to pervious experiments using cryogenic optical resonators (COREs), but relying solely on Earth's rotation, this new version is expected to lead to orders of magnitude improvement in sensitivity to Lorentz-Invariance violation. We present the initial results of this experimental effort at the $\Delta $c($\theta )$/c $\sim $ 10$^{-16}$ level for an direction dependent variation of the speed of light and discuss the potential for future improvements.