Pushing Metacavities to the Quantum limit and beyond

We present the progress in the field of optical cavities with metamirrors (metacavities). Metamirrors show theoretically on one hand the lowest thermal noise of all mirror technologies and on the other hand principally enable high reflectivity in combination with high spectral and angular tolerances. First experimental results on metamirrors in cavity experiments are presented. The reflectivity of the metamirrors are investigated using a two-stage experimental setup covering the reflectivity range of 0.2% up to almost 100%. We show spectroscopic measurement results for wavelengths ranging from 1450 to 1650 nm as well as reflectivity measurements using a cavity ringdown setup. The manifold capabilities of integrating multiple optical functions with one nanostructured layer pave the way to polarization-dependent mirrors, focusing elements, more effective squeezed-light cavities and ultra-stable metamirror cavities.