Thermal noise in a high Q cryogenic resonator

In order to evaluate the feasibility of a mixed mechanical and electrical m ultimode matching network for a resonant gravitational wave detector, curre nt noise measurements were performed on a high quality factor inductance-ca pacitance resonator, based on a superconducting coil, by using a dc superco nducting quantum interference device weakly coupled to the coil. We present a method to identify different noise sources in the system by their depend ence on the temperature or on the resonator quality factor. Measurements pe rformed at quality factors up to 10(6) in the temperature range 1.2-4.2 K, show that the total measured noise is only contributed by the resonator the rmal noise. (C) 1999 American Institute of Physics. [S0034-6748(99)04503-7] .