  QUBIC is an instrument aiming at measuring the B mode polarisation
anisotropies at medium scales angular scales (30-200 multipoles). The search
for the primordial CMB B-mode polarization signal is challenging, because of
many difficulties: smallness of the expected signal, instrumental systematics
that could possibly induce polarization leakage from the large E signal into B,
brighter than anticipated polarized foregrounds (dust) reducing to zero the
initial hope of finding sky regions clean enough to have a direct primordial
B-modes observation. The QUBIC instrument is designed to address all aspects of
this challenge with a novel kind of instrument, a Bolometric Interferometer,
combining the background-limited sensitivity of Transition-Edge-Sensors and the
control of systematics allowed by the observation of interference fringe
patterns, while operating at two frequencies to disentangle polarized
foregrounds from primordial B mode polarization. Its characteristics are
described in details in this Technological Design Report.
