# QUIET

QUIET

An illustration of the completed QUIET telescope on the CBI platform.
Organization International collaboration
Location Llano de Chajnantor Observatory
Altitude 5,080 m
Wavelength 40 and 90 GHz
Telescope style 4 telescopes
Diameter Three 2 m, one 7 m
Angular resolution Few arcminutes to several degrees
Website quiet.uchicago.edu

QUIET is an astronomy experiment to study the polarization of the cosmic microwave background radiation.[1] QUIET stands for Q/U Imaging ExperimenT. The Q/U in the name refers to the ability of the telescope to measure the Q and U Stokes parameters simultaneously. QUIET is located at an elevation of 5,080 metres (16,700 feet) at Llano de Chajnantor Observatory in the Chilean Andes.[2] It began observing in late 2008 and finished observing in December 2010.[3]

QUIET is the result of an international collaboration that has its origins in the CAPMAP, Cosmic Background Imager (CBI) and QUaD collaborations. The collaboration consists of 7 groups in the United States (the California Institute of Technology, the University of Chicago, Columbia University, the Jet Propulsion Laboratory, the University of Miami, Princeton University and Stanford University), 4 groups in Europe (the University of Manchester, the Max-Planck-Institut für Radioastronomie Bonn, the University of Oslo and the University of Oxford) and one group in Japan (KEK; the first time a Japan group has been involved in CMB studies). Other members of the collaboration are from the University of California, Berkeley, the Goddard Space Flight Center and the Harvard-Smithsonian Center for Astrophysics.[1]

## Instrument

QUIET will have arrays of detectors at two frequencies: 40 GHz (Q band) and 90 GHz (W band). It will use four telescopes, three of which will be purpose-built 2 m ones with the other being the 7 m Crawford Hill telescope currently used for CAPMAP. As a result, it will have angular resolutions between a few arcminutes and several degrees. The detectors are mass-produced coherent correlation polarimeters.[1][4]

The instrument is being constructed in three phases. The first phase consisted of a 7-element 90 GHz array to demonstrate the technology. The second phase aims to mount a 91-element 90 GHz array (with 18 GHz bandwidth) and a 19-element 40 GHz array (with 8 GHz bandwidth) on 1.4 m cassegrain telescopes, mounted on what is currently the CBI platform. It is expected that these will start observing in 2008. The third phase aims to construct four further arrays by around 2010. Two of these will be at 40 GHz, with 91 elements each, and the other two will be at 90 GHz, with 397 elements each. These will then be mounted on three 2 m dishes on the CBI platform and the 7 m telescope.[5][6]

The instrument is located at a height of 5,080 m at Llano de Chajnantor Observatory in the Chilean Andes. The site is owned by the Chilean government, and is leased to the Atacama Large Millimeter Array. The site was selected due to the altitude, current infrastructure and accessibility, as well as the low humidity of the site, which reduces the contamination of the detected signals by the atmosphere.[2]

## Science

The QUIET telescope with its ground screen raised

QUIET will measure the polarization of the cosmic microwave background radiation (CMB). This polarization is commonly split into two components: E-modes, which represent the gradient component, and B-modes, which give the curl component. It is thought that B-modes are formed both from primordial fluctuations due to cosmic inflation, and from gravitational lensing of the CMB. As of 2008, only E-modes have been detected. QUIET aims to detect and characterize the B-modes polarization for the first time, and to provide more accurate measurements of the E-mode polarization.[4]

B-modes are thought to be much fainter than E-modes, as they are formed by higher order effects. The ratio of the E-mode to B-mode polarization is currently unknown, and the minimum detectable value of this can be used as a measure of the sensitivity of a CMB instrument. For QUIET this value is r=0.009, which corresponds to the energy scale of cosmic inflation being around $10^{16}$ GeV.[4]

QUIET's measurements of the CMB's power spectrum will be between the multipoles of about 40 and 2,500, and will be made in a section of the sky known to have low foreground contamination.[4]

## Status

As of March 2011, the QUIET team described the status

Observations were made from October 2008 through May 2009 using a 19-element 40 GHz instrument coupled to a 1.4 meter telescope located at the Llano de Chajnantor Observatory in Chile. Observations with a 91-element 90 GHz instrument on the same telescope finished in December 2010. The QUIET instrument has been dismantled from the old CBI mount.

## References

1. ^ a b c "QUIET (Q/U Imaging ExperimenT)". QUIET collaboration. 17 February 2008. Retrieved 2008-05-24.
2. ^ a b "QUIET: Site". QUIET collaboration. 27 January 2008. Retrieved 2008-05-24.
3. ^ QUIET Collaboration; Bischoff; Brizius; Buder; Chinone; Cleary; Dumoulin; Kusaka et al. (2010). "First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475". arXiv:1012.3191v2 [astro-ph.CO].
4. ^ a b c d "QUIET: Science". QUIET collaboration. 27 January 2008. Retrieved 2008-05-24.
5. ^ Samtleben (2008)
6. ^ "QUIET: Instrumentation". QUIET collaboration. 27 January 2008. Retrieved 2008-05-24.