  A prototype version of the Q & U bolometric interferometer for cosmology
(QUBIC) underwent a campaign of testing in the laboratory at Astroparticle
Physics and Cosmology laboratory in Paris (APC). The detection chain is
currently made of 256 NbSi transition edge sensors (TES) cooled to 320 mK. The
readout system is a 128:1 time domain multiplexing scheme based on 128 SQUIDs
cooled at 1 K that are controlled and amplified by an SiGe application specific
integrated circuit at 40 K. We report the performance of this readout chain and
the characterization of the TES. The readout system has been functionally
tested and characterized in the lab and in QUBIC. The low noise amplifier
demonstrated a white noise level of 0.3 nV.Hz^-0.5. Characterizations of the
QUBIC detectors and readout electronics includes the measurement of I-V curves,
time constant and the noise equivalent power. The QUBIC TES bolometer array has
approximately 80% detectors within operational parameters. It demonstrated a
thermal decoupling compatible with a phonon noise of about 5.10^-17 W.Hz^-0.5
at 410 mK critical temperature. While still limited by microphonics from the
pulse tubes and noise aliasing from readout system, the instrument noise
equivalent power is about 2.10^-16 W.Hz^-0.5, enough for the demonstration of
bolometric interferometry.
