The quest for B-mode polarization of the Cosmic Microwave Background is among the main challenges in Observational Cosmology. Measurement of B-mode polarization in the CMB will be clear evidence of the presence of primordial gravitational waves which are theoretically expected to be produced during inflation about 10-35 seconds after the Planck epoch. The B-mode measurement is perhaps the most difficult cosmological challenge because the expected signal is very small.  It requires high sensitivity and negligible instrument systematic effects with wide frequency coverage in order to separate the primordial signal from foreground emissions.

QUBIC (QU Bolometric Interferometer for Cosmology: ​​) is a novel instrument concept dedicated to the search for B-modes by measuring the Q and U polarization modes. It brings together the advantages of bolometers with high sensitivity and those of interferometers that have exquisite control of instrument systematic effects. The interferometric nature of QUBIC also allows spectro-imaging and improved spectral resolution with respect to imagers, providing a significant advantage concerning foreground removal. The Technological Demonstrator is under test at APC since 2019 and will be installed at the QUBIC site at 5000m a.s.l. in the province of Salta in Argentina in 2021.

The Ph.D. student will take part in the integration and characterization phase on-site where all the performances of the instrument will be checked and modeled with simulations that she/he will contribute to building with all the QUBIC collaboration. One of the critical points is the characterization of the superconducting detectors and the associated readout electronics. Measurements in other cryogenic testbeds in the lab can also be carried on in order to build the detailed physics model of the detectors and the readout electronics. The Ph.D. student is expected to contribute significantly to the integration and characterization of the instrument on-site, as well as to the analysis of the first scientific observation runs.

The student will work within the QUBIC team at APC, collaborating with the rest of the collaboration in France, Italy, Ireland, and Argentina. He/She may also contribute to other scientific activities in parallel to his/her specific topic. These might include the development of the QUBIC Data Analysis pipeline from time-domain to cosmological constraints, self-calibration and instrumental systematic effects control, spectro-imaging and astrophysical foreground contamination control, machine-learning techniques applied to CMB data analysis.


Michel Piat, Steve Torchinsky






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