Silicon nitride membrane resonators at millikelvin temperatures with quality factors exceeding 10^8

We study the mechanical dissipation of the fundamental mode of millimeter-sized, high quality-factor (Q) metalized silicon nitride membranes at temperatures down to 14?mK using a three-dimensional optomechanical cavity. Below 200?mK, high-Q modes of the membranes show a diverging increase of Q with decreasing temperature, reaching Q=1.27×108Q=1...

Microwave-induced excess quasiparticles in superconducting resonators measured through correlated conductivity fluctuations

We have measured the number of quasiparticles and their lifetime in aluminium superconducting microwave resonators. The number of excess quasiparticles below 160?mK decreases from 72 to 17??m?3 with a 6?dB decrease of the microwave power. The quasiparticle lifetime increases accordingly from 1.4 to 3.5?ms. These properties of the superconductor...