QUBIC: The QU bolometric interferometer for cosmology E. Battistelli e , A. Baú f , D. Bennett l , L. Bergé c , J.-Ph. Bernard b , P. de Bernardis e , G. Bordier a , A. Bounab b , É. Bréelle a , E.F. Bunn j , M. Calvo e , R. Charlassier a , S. Collin c , A. Coppolecchia e , A. Cruciani e , G. Curran l , L. Dumoulin c , A. Gault i , M. Gervasi f , A. Ghribi a , M. Giard b , C. Giordano e , Y. Giraud-Héraud a , M. Gradziel l , L. Guglielmi a , J.-Ch. Hamilton a,⇑ , V. Haynes g , J. Kaplan a , A. Korotkov h , J. Landé b , B. Maffei g , M. Maiello m , S. Malu k , S. Marnieros c , J. Martino a , S. Masi e , A. Murphy l , F. Nati e , C. O’Sullivan l , F. Pajot d , A. Passerini f , S. Peterzen e , M. de Petris e , F. Piacentini e , M. Piat a , L. Piccirillo g , G. Pisano g , G. Polenta e,n,o , D. Prêle a , D. Romano e , C. Rosset a , M. Salatino e , A. Schillaci e , G. Sironi f , R. Sordini e , S. Spinelli f , A. Tartari f , P. Timbie i , G. Tucker h , L. Vibert d , F. Voisin a , R.A. Watson g , M. Zannoni f , The QUBIC collaboration a APC, Université Paris, Diderot-Paris 7, CNRS/IN2P3, CEA, Observatoire de Paris, 10, rue A. Domon & L. Duquet, Paris, France b Centre d’Étude Spatiale des Rayonnements, CNRS/Université de Toulouse, 9 Avenue du colonel Roche, BP 44346, 31028 Toulouse Cedex 04, France c Centre de Spectroscopie Nucléaire et de Spectroscopie de Masse, UMR8609 IN2P3-CNRS, Univ. Paris Sud, bât 108, 91405 Orsay Campus, France d Institut d’Astrophysique Spatiale, Universite Paris-Sud, Orsay 91405, France e Dipartimento di Fisica, Università di Roma ‘‘La Sapienza’’, Roma, Italy f Dip. di Fisica ‘‘G.Occhialini’’- Università degli Studi di Milano-Bicocca Piazza della Scienza, 3 - 20126 Milano, Italy g School of Physics and Astronomy, The University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK h Brown University, Providence, RI 02912, USA i University of Wisconsin-Madison, Madison WI 53706, USA j Physics Department, University of Richmond, Richmond, VA 23173, USA k Raman Research Institute, Sadashivanagar, Bangalore 560 080, India l Department of Experimental Physics, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland m Universitá degli Studi di Siena - Rettorato, Via Banchi di Sotto 55, 53100 Siena, Italy n ASI Science Data Center, c/o ESRIN, via G. Galilei, I-00044 Frascati, Italy o INAF, Osservatorio Astronomico di Roma, via di Frascati 33, I-00040, Monte Porzio Catone, Italy article info Article history: Received 3 November 2010 Received in revised form 26 January 2011 Accepted 26 January 2011 Available online 2 February 2011 Keywords: Cosmology Cosmic Microwave Background Inflation Instrumentation Bolometric interferometry abstract One of the major challenges of modern cosmology is the detection of B-mode polarization anisotropies in the Cosmic Microwave Background. These originate from tensor fluctuations of the metric produced dur- ing the inflationary phase. Their detection would therefore constitute a major step towards understand- ing the primordial Universe. The expected level of these anisotropies is however so small that it requires a new generation of instruments with high sensitivity and extremely good control of systematic effects. We propose the QUBIC instrument based on the novel concept of bolometric interferometry, bringing together the sensitivity advantages of bolometric detectors with the systematics effects advantages of interferometry. The instrument will directly observe the sky through an array of entry horns whose signals will be com- bined together using an optical combiner. The whole set-up is located inside a cryostat. Polarization mod- ulation will be achieved using a rotating half-wave plate and the images of the interference fringes will be formed on two focal planes (separated by a polarizing grid) tiled with bolometers. We show that QUBIC can be considered as a synthetic imager, exactly similar to a usual imager but with a synthesized beam formed by the array of entry horns. Scanning the sky provides an additional modu- lation of the signal and improve the sky coverage shape. The usual techniques of map-making and power spectrum estimation can then be applied. We show that the sensitivity of such an instrument is compa- rable with that of an imager with the same number of horns. We anticipate a low level of beam-related systematics thanks to the fact that the synthesized beam is determined by the location of the primary horns. Other systematics should be under good control thanks to an autocalibration technique, specific to our concept, that will permit the accurate determination of most of the instrumental parameters that would otherwise lead to systematics. Ó 2011 Elsevier B.V. All rights reserved. 0927-6505/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.astropartphys.2011.01.012 ⇑ Corresponding author. E-mail address: hamilton@apc.univ-paris7.fr (J.-Ch. Hamilton). Astroparticle Physics 34 (2011) 705–716 Contents lists available at ScienceDirect Astroparticle Physics journal homepage: www.elsevier.com/locate/astropart