Officially inaugurated in Argentina, the QUBIC (Q&U Bolometric Interferometer for Cosmology) telescope is an innovative tool that will observe the cosmic microwave background, the residual echo of the Big Bang, from a high-altitude (5000 m) desert site in the Argentine Andes, near San Antonio de Los Cobres. The ceremony, which included a visit to the telescope, was attended by representatives of the project’s funding institutions and the international scientific team.
Italy is playing a leading role in the project thanks to scientific and technological contributions from the INFN (National Institute for Nuclear Physics) and the University of Milan, University of Milan-Bicocca, ‘Tor Vergata’ University of Rome and Sapienza University of Rome.
QUBIC will focus on measuring the signal caused by the interaction of primordial gravitational waves with the electromagnetic radiation that permeates the universe.
Following its development and integration at the European laboratories of the universities and research institutions involved in the collaboration, QUBIC arrived in Argentina, in the city of Salta, in July 2021, where it was calibrated and tested in a laboratory. The results of these activities are reported in eight articles that appeared in the ‘Journal of Cosmology and Astroparticle Physics’ in April this year and confirmed the correct functioning of the instrument and bolometric interferometry, i.e. the newly developed technique on which QUBIC’s observations will be based, which combines the very high sensitivity of bolometric detectors cooled to near absolute zero (-273 °C) with the precision of interferometric instruments.
The goal of observing the very weak polarisation effects in the microwaves that originated in the very early stages of the expansion of the universe after the Big Bang, i.e. the direction in which the associated electromagnetic field oscillates as it spreads, made it necessary to develop and build a complex and unique instrument. Today, QUBIC is a unique resource in the world of primordial universe measurements.
“There is no other way to experimentally investigate – with ground-based experiments – phenomena that are thought to have occurred during the so-called ‘cosmic inflation’, which involved a terrifyingly large amount of energy. QUBIC is therefore important for both cosmology and fundamental physics,” explains Silvia Masi, a lecturer at Sapienza University of Rome and INFN researcher, who is coordinating the Italian participation in the experiment.
“QUBIC,” adds Oliviero Cremonesi, president of the INFN National Scientific Commission for Astroparticle Physics Research, “aims to measure the polarisation of the cosmic microwave background with a unique possibility of detecting the marks left by gravitational waves released in the first moments of the universe.”
The effectiveness of QUBIC and the measurement method used to study the primordial universe were verified by the collaboration during the long period between the first tests conducted in the laboratory, in Paris, and the arrival of the instrument in Argentina, at the laboratory in Salta, where the first observations of the sky were made. The installation of the experiment in San Antonio de Los Cobres, which took place during October, therefore marks a success that comes at the end of a long period of preparation and which will allow ultra-sensitive measurements to begin thanks to the extraordinary transparency and stability of the observation site’s atmosphere.
“The QUBIC installation team, in which Francesco Cavaliere, workshop manager at the University of Milan, also participated, did an excellent job in a very short time, under particularly challenging conditions due to the altitude and strong winds at high altitude. The first measurements will demonstrate ‘in the field’ the effectiveness of bolometric interferometry by observing astronomical sources. In approximately one year’s time, the instrument will also be made even more competitive by increasing the number of antennas and detectors, so that it will be able to perform perform cosmologically significant measurements within three years,” explains Aniello Mennella, a lecturer at Milan University and INFN researcher.
“Measurement of such a weak signal,” specifies Mario Zannoni, a lecturer at the University of Milan-Bicocca and INFN researcher, “will only be considered free of systematic errors if there are consistent results from very different instruments. This is precisely why QUBIC, as the only bolometric interferometer, is an irreplaceable resource in the study of the universe’s early life.”
“Thanks to its multispectral and self-calibration capabilities, QUBIC will produce data that are completely original and complement those of the other experiments, offering researchers countless possibilities for cross-checking and therefore exceptionally reliable results,” concludes Giancarlo De Gasperis, a researcher at the Physics Department of the ‘Tor Vergata’ University of Rome and INFN.
QUBIC is the result of a collaboration between 130 researchers, engineers and technicians in France, Italy, Argentina, Ireland and the UK. The instrument was integrated in Paris at the APC laboratories in 2018 and calibrated during 2019-2021.
The Italian contribution was fundamental to the development of the instrument and will continue to be so in the experiment’s subsequent phases. The instrument is housed in a cryostat, built in the laboratories of La Sapienza and the Rome section of the INFN, capable of cooling not only the detectors, but also the interferometer’s entire optical system to near absolute zero. The same group also created the cryo-mechanical system that permits measurement of the radiation’s polarisation state. Other cryogenic components, which work at a temperature below -270 °C, are also Italian, such as the highly advanced corrugated antennas that collect radiation from the sky, made in the laboratories of the University and the INFN section at Milan University, while the optics that focus it on the detectors and the shutter system that makes it possible to vary the configuration of the interferometer and self-calibrate it are made by the University and INFN Section of Milan-Bicocca.
“The start of QUBIC data collection is a concrete sign of INFN’s interest in cosmic background radiation research and was also made possible thanks to a significant contribution from INFN,” concludes INFN Executive Board member Marco Pallavicini.