Abstract
The Q/U Imaging ExperimenT (QUIET) is a project aiming to measure the predicted B-mode polarization of the Cosmic Microwave Background (CMB) radiation and improve the characterization of the E-mode component. The CMB was generated 380,000 years after the Big Bang during a period known as recombination, once the universe had expanded enough to cool to a temperature of 3,600 K. This relic radiation provides crucial information about the large-scale physical conditions and processes prevailing up to and during that period. The prediction of B-mode polarization arises from cosmological models in which the universe underwent an inflationary phase that occurred 10^-35 s after the Big Bang, and lasted 10^-32 s. Inflation propagated original quantum fluctuations in space-time to the post-inflationary period in the form of gravitational waves, which produced ripples in space and polarization of the CMB in the form of E- and B-mode patterns. Scalar density perturbations were also propagated by the inflation but derived in the formation of E-modes only. The detection of B-mode polarization would thus provide strong support to the inflationary scenario that considers the existence of primordial gravitational waves. The expected level of this signal is ~ 10^-8 K and its measurement represents an enormous scientific and technical challenge. The QUIET telescope observed the microwave sky with two arrays of polarimeters operating at 43 and 94 GHz. It was located in the Chilean Andes and collected more than 10,000 hours of data between October 2008 and December 2010. The detector elements are based on state-of-the-art Monolithic Microwave Integrated Circuit (MMIC) technology and were designed to provide simultaneous measurements of the Q and U Stokes parameters of the sky, improving the efficiency and sensitivity of the instrument. This thesis describes the design of the QUIET telescope, the observations conducted, and the results of the data analysis. The attention is centered on the analysis of calibration data gathered through the observation of astronomical sources such as the Crab nebula and Jupiter in order to characterize the telescope beam patterns, responsivities and instrumental polarization. Finally, the impact of these quantities and their uncertainties on the CMB results is addressed.