Measurements of the cosmic microwave background (CMB) radiation can reveal with remarkable precision the conditions of the Universe when it was ∼400,000 years old. The three most fundamental properties of the CMB are its frequency spectrum (which determines the temperature), and the fluctuations in both the temperature and polarization across a range of angular scales. The frequency spectrum has been well determined, and considerable progress has been made in measuring the power spectrum of the temperature fluctuations. But despite many efforts to measure the polarization, detection of this property of the CMB has hitherto been beyond the reach of even the most sensitive observations. Here we describe the Degree Angular Scale Interferometer (DASI), an array of radio telescopes, which for the past two years has conducted polarization-sensitive observations of the CMB from the Amundsen-Scott South Pole research station.
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Acknowledgements We are indebted to the Caltech CBI team led by T. Readhead, in particular to S. Padin for a considerable fraction of DASI’s electronics design, to J. Cartwright for the downconverter design and to M. Shepherd for data acquisition software. E. Chauvin of Vertex/RSI is thanked for professional excellence in the design and delivery of the telescope mount. We thank Raytheon Polar Services for their support of the DASI project, including the erection of the DASI ground shields, and in particular R. Rowatt and his crew. We are indebted to the Center for Astrophysical Research in Antarctica (CARA), in particular the efforts of A. Day, S. Meyer, N. Odalen, R., D. and E. Pernic, R. Lowenstein, R. Spotz, M. Whitehead and the CARA polar operations staff. We thank J. Kooi for his assistance with the installation of the polarization hardware, J. Yamasaki for help with electronics, E. LaRue and G. Drag for the assembly of the calibration wire grids, M. Loh for assistance with the Sun shield and K. Coble for analysis of DASI primary beam measurements. We thank the TopHat collaboration for the use of their Sun shield. We thank the observatory staff of the Australia Telescope Compact Array, in particular B. Sault and R. Subrahmanyan, for their generosity in providing point source observations of the DASI fields. This research was initially supported by the National Science Foundation (NSF) under a cooperative agreement with CARA, a NSF Science and Technology Center; it is currently supported by the NSF-OPP. J.E.C. acknowledges support from the James S. McDonnell Foundation and the David and Lucile Packard Foundation. J.E.C. and C.P. acknowledge support from the Center for Cosmological Physics.