QUBIC-ON-SKY

The quest for B-mode polarization of the Cosmic Microwave Background (CMB) is among the major challenges of observational cosmology. It would reveal primordial gravitational waves, validating inflation theory, with consequences in particle physics. The expected signal is weak (polarization of tens of nK on an unpolarized 3K background), requiring high sensitivity detectors. QUBIC is an instrument based on Bolometric Interferometry (BI), a new concept combining high sensitivity from bolometers and powerful systematics control from interferometry. Compared to other similar projects, QUBIC has the unique feature of spectral imaging: foregrounds can be mitigated by measuring their spectral properties within the physical band of the instrument. After laboratory testing of the Technological Demonstrator (TD), identical to the “Full Instrument” (FI) but with fewer detectors and baselines, French/Italian agencies reviewed and validated its performance. The instrument is already in Argentina, cooled-down, operational, and being tested indoors in Salta. Installation and commissioning of the TD at the observing site are scheduled for early 2022. A first upgrade will complete the FI after one year only requiring procurement and integration of already validated subsystems. QUBIC alone will achieve ?(r)=0.015 with 3 years of data (without adding Planck), with enhanced spectral resolution and constraints on foreground contamination with respect to competitors thanks to spectral-imaging. A later upgrade (QUBIC+) is anticipated after the FI, aiming at ?(r)=0.001 using delensing. QUBIC is the only B-mode detector conceived and constructed with new technologies in Europe. The outcome of its exploitation, a measurement of the B-mode amplitude, will be a highlight at the heart of modern cosmology. This proposal seeks support for the QUBIC science operations (TD and FI) over a 48 months period.