Bolometric Adding Interferometry: MBI & QUBIC

1. Bolometric Adding Interferometry:MBI & QUBIC Peter Timbie University of Wisconsin - Madison The Path to CMBPol

2. CMB Interferometers

3. Why CMB Interferometry? Systematics! • simple optics • - beams can be formed with corrugated horn arrays • symmetric beam patterns, low sidelobes, no mirrors • - no off-axis aberrations • correlates Ex and Ey on a single detector to measure Stokes U (no differencing of detectors) • differences sky signals (measures visibilities) without scanning • simple observing strategy - measure U and Q on each field by rotating about optical axis • measures Temp and Polarization power spectra directly • angular resolution ~ 2X better than imager of equivalent diameter • coherent (HEMTs) or incoherent (bolometers) systems possible

4. Interferometer Beam Systematics Interferometers measure visibilities: n1 n2 y i uij j x X Beam mismatch, distortion, etc. do not couple T into Stokes U visibility. [E.F. Bunn PRD 75, 083517 (2007)]

5. Beam Combination for Large N • Pairwise (Michelson): signals are split and combined pairwise • N(N-1)/2 pairs (78 for N = 13, 4950 for N =100) • multiplying correlator (coherent receivers only) a. analog (DASI/CBI) b. digital (most radio interferometers) - power? - bandwidth? • Fizeau (Butler): signals from all antennas appear at all detectors • Guided-wave adding interferometer (Butler combiner, Rotman lens) • Quasioptical adding interferometer using a telescope (MBI, EPIC-I, QUBIC)

6. Ryle’s Adding Interferometer (1952) “visibility”

7. // // //    …. …. Adding Interferometerfor Many Horns N horns OMTs 2Nphase modulators beam combiner detectors single-horn auto-correlation Stokes U visibilities Stokes I visibilities total power

8. Quasioptical Beam Combiner Cryostat Feed horn antennas Phase Shifters 45° CW twist rectangular wave guide 45º CCW twist rectangular wave guide Bolometer Array Parabolic mirror

9. 1 baseline 1 baseline 1 baseline total signal 1 horn Interference pattern • The interference pattern is imaged on the bolometer array • Each pixel measures a linear combination of all visibilities with different phase shifts • Sequences of phase shift modulations allow reconstruction of all visibilities in optimal way • In a close-packed array, many baselines are redundant - these need to be ‘co-added’ [Charlassier et al., arxiv:0806.0380, A&A 497 (2009) 963] [Hyland et al., arXiv :0808.2403v1, MNRAS 393 (2009) 531]

10. Sensitivity - comparison to imager Both systems have: • 256 horns • 1 angular resolution • background-limited bolos • 25 % bandwidth Interferometer: • co-adds ‘redundant’ visibilities • has 1000 detectors data pts from simulation [Hamilton et al., arxiv:0807.0438, A&A 491-3 (2008) 923-927] updated with bandwidth and accurate NET calculations]

11. Fizeau (optical) beam combiner • 4 feedhorns (6 baselines) • 90 GHz (3 mm) • ~1o angular resolution • 7o FOV Antennas Phase modulators The Millimeter-Wave Bolometric Interferometer (MBI-4) Liquid nitrogen tank Liquid helium tank Secondary mirror 3He refrigerator Primary mirror Bolometer unit

12. MBI Assembly 15 cm 19 spider-web bolos (JPL) (PSB’s not required)

13. MBI Team

14. MBI-4 at Pine Bluff ObservatoryMadison, WI • First light March 2008 • Beam maps March 2009 • See poster by Amanda Gault

15. MBI-4 interference fringes Observed Signal (Bolometer #9) Simulated Signal • Baseline formed by horns 2 and 3 • Observed Gunn oscillator on tower

16. MBI Interference Fringes

17. The QUBIC collaboration University of Wisconsin USA A merging of MBI (USA) with BRAIN (Europe) IAS Orsay France CSNSM Orsay France University of Richmond USA Maynooth University Ireland APC Paris France Brown University USA Universita di Milano-Bicocca Italia IUCAA, Pune India La Sapienza, Roma, Italia Manchester University UK CESR Toulouse France QU Bolometric Interferometer for Cosmology Google Maps

18. phase shifters horns Bolometer array The QUBIC instrument concept Sky ~25 cm • Off-axis quasi-optical beam combiner 4K 4K 4K back horns 4K ~60 cm ~40 cm 4K ~10 cm Cryostat 300 mK ~70 cm

19. Primary (entry) horns QUBIC (144x6, ( Secondary (reemitting) horns Significance QUBIC Design ~ 25cm 6 modules of 144 entry horns • 14 deg. primary beams • square compact configuration • multipole range : 25-150 • ~900 TES bolometers / module • ~10000 baselines / module • phase switch redundant baselines simultaneously - phase steps of 15 degrees - sequence length ~500 steps 3 channels: 90,150,220 GHz 25% Bandwidth Modular Cryogenics • One 4K pulse tube for 6 modules • 100 mK focal plane r ~ 0.01 in one year of data

20. QUBIC program 2006 MBI-4 BRAIN Pathfinder 2007 • MBI-4 Prototype • 4 horns bolometric interferometer • works in Wisconsin (2008 and 2009) • Fringes observed ! • BRAIN Pathfinder • Site testing, logistics • Atmosphere characterization at Dome C • (effective temperature, polarization ...) • 2 campaigns, January 2006 and 2007 • Third campaign starting next Antarctic summer • QUBIC • Search for primordial B-modes (50 < l < 150) • 6 Bolometric interferometer modules • 144 horns/module (90, 150, 220 GHz) • 25% Bandwidth • Full instrument in 2012-2013 • Target : r ~ 0.01 in 1 year of data 2008 2009 2010 QUBIC first module 2011 QUBIC 2012

21. Next steps for Bolometric Interferometry • phase modulators are critical • multiple phase states (~ 5 bits) • 1 ms switching speed • several technologies under study: Faraday, MEMs, s/c nanobridge switches, varactor diode • simulations of systematic effects, scan strategies • foreground removal in visibility space • QUBIC • see poster by T.K. Sridharan for alternate BI approach