An illustration of the completed QUIET telescope on the CBI platform.
|Location||Llano de Chajnantor Observatory|
|Wavelength||40 and 90 GHz|
|Telescope style||4 telescopes|
|Diameter||Three 2 m, one 7 m|
|Angular resolution||Few arcminutes to several degrees|
QUIET is an astronomy experiment to study the polarization of the cosmic microwave background radiation. 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 will be located at an elevation of 5,080 metres (16,700 feet) at Llano de Chajnantor Observatory in the Chilean Andes. It is expected to start observing around 2008.
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.
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.
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.
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.
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.
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 1016 GeV.