The MiniGRAIL detector is a cryogenic 68 cm diameter spherical gravitational wave antenna made of CuAl(6%) alloy with a mass of 1400 Kg and a resonance frequency of 2.9 kHz. Unlike other types of... Show moreThe MiniGRAIL detector is a cryogenic 68 cm diameter spherical gravitational wave antenna made of CuAl(6%) alloy with a mass of 1400 Kg and a resonance frequency of 2.9 kHz. Unlike other types of gravitational wave detectors, a single sphere is capable of determining direction and polarization of GW signal, because it has five degenerate modes of oscillation that interact with gravitational waves. This thesis is focused on building the full acquisition system and preparation of MiniGRAIL for a scientific run, with a full read-out configuration at millikelvin temperatures. We have also performed a test run to evaluate the calibration procedure we developed. During the run we have reached a peak strain sensitivity of 3E-20 Hz^(-1/2) at 4.2K. For current system configuration and thermodynamic temperature of the sphere of 20 mK, the estimated peak sensitivity level is 2E-22 Hz^(-1/2) and the minimal detectable Fourier amplitude of gravitational wave burst of 1E-22. In the last chapter of the thesis we present a SQUID-based scheme to measure the displacement of a nanomechanical resonator at cryogenic temperature. We demonstrate its potential by cooling an ultrasoft silicon cantilever to a noise temperature of 25 mK, corresponding to a subattonewton thermal force noise of 0.5 aN/Hz^(1/2). Show less
