Exploring Primordial Universe w/ QUBIC: 400 Horns at 100 mK in Antarctica

[marcus]

http://arxiv.org/abs/1010.0645

Cryogenic, 400 horns, Antarctica, detector plate at 100 milliKelvin

"One of the major challenges of modern cosmology is the detection of B-mode polarization anisotropies in the CMB. These originate from tensor fluctuations of the metric produced during the inflationary phase. Their detection would therefore constitute a major step towards understanding 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..."

See the schematic diagram of the device, Figure 1, on page 3. Much of the device is enclosed in a crygenic box at 4 Kelvin. The imaging plate is at lower temperature (100 milliKelvin.)

"We plan to install a first QUBIC module at the Franco-Italian Concordia station in Dome C, Antarctica within two years. The first modulewill consist of an array of 400 horns operating at 150 GHz with 25% bandwidth and 14 degree (FWHM) primary beams. The optical combiner will have a focal length of ∼30cm and each of the two focal planes will be comprised of arrays of 30x30 bare TES bolometers of 3mm size. The full instrument will include modules at three different frequencies (90,150,220 GHz) and will constrain a tensor to scalar ratio of 0.01 in one year of data taking at the 90% confidence level..."

 

[wolram]

This is very exciting for me, i hope every thing goes to plan.

 

[marcus]

Yes Wooly! It is exciting. A new kind of instrument. You probably looked at the diagram of the layout, with the horns and the two mirrors and the bolometric plate array.

It's intriguing, but it is also too new for me to have any way to judge it. Also I could not tell from the article whether or not they had gotten funding.

They are talking about having something operating at Antarctica within two years. How can they be talking about a two year schedule if they don't have funding. So I must assume they have already assurance of the money and technical support. But I could not find explicit confirmation.

Hopefully someone else who knows something more about this will see our thread and comment. Until we know more, we have to keep open the possibility that this idea for a new instrument in crazy and will not work.

The general idea is that ancient gravitational ripples are IMPRINTED in the polarization picture of the CMB (cosmic microwave background). Current instruments only map the temperature variation. If we had a map of the polarization, we could see the wavelengths of these ancient ripples. The power spectrum (how much ripple at long wavelengths, how much ripple at shorter, and still shorter). This would tell something about the random graviational disturbances that were happening in early universe. I think that's a fair intuitive overview.

I think maybe the Planck spacecraft , currently taking data, is somewhat sensitive to polarization, but not sensitive enough. So there is a motive for people to conceive of these loony-looking cryogenic Antarctic instruments with their arrays of horns.

If they do have funding, that will mean that the concept has passed some kind of critical review. I hope it has and wish them all success.