Thermal noise in a high Q ultracryogenic resonator

A high Q electrical resonator based on a superconducting coil and a low loss capacitor has been realized and characterized at temperatures down to 60 mK. The resonance frequency is near 10 kHz, and the quality factor is higher than 10(5). The main purpose of the experiment is to test the feasibility of cooling to ultracryogenic temperatures the readout of the gravitational wave detector AURIGA, which is based on a high Q resonant electrical matching network. The resonator current noise, measured by a superconducting quantum interference device amplifier, scales with temperature in the full range 60 mK-4.2 K, showing that the system is thermal noise limited and its dissipating elements are well thermalized. Some implications of these results and possible applications are discussed. (c) 2005 American Institute of Physics