QUBIC III: Laboratory Characterization

TL;DR

This paper reports laboratory tests of the QUBIC III prototype, demonstrating the feasibility of bolometric interferometry for cosmology through beam, interference, and polarization measurements.

Contribution

It provides the first laboratory characterization of QUBIC III, confirming its design and polarization performance for future cosmological observations.

Findings

Beam matches theoretical simulations

Polarization rejection less than 0.5%

Prototype ready for deployment in Argentina

Abstract

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 in Paris. We report the results of this Technological Demonstrator which successfully shows the feasibility of the principle of Bolometric Interferometry. Characterization of QUBIC includes the measurement of the synthesized beam, the measurement of interference fringes, and the measurement of polarization performance. A modulated and frequency tunable millimetre-wave source in the telescope far-field is used to simulate a point source. The QUBIC pointing is scanned across the point source to produce beam maps. Polarization modulation is measured using a rotating Half Wave Plate. The measured beam matches well to the theoretical simulations and gives QUBIC the ability to do spectro imaging. The polarization performance is excellent with less than 0.5\% cross-polarization rejection. QUBIC is ready for deployment on the high altitude site at Alto Chorillo, Argentina to begin scientific operations.