QUaD

QUaD
Name	QUaD
Caption	QUaD telescope at the South Pole
Country	United States
Operator	Princeton University; University of Chicago
Location	Amundsen–Scott South Pole Station
Established	2005
Decommissioned	2007
Wavelength	3.2 mm and 2.0 mm
Type	Cassegrain radio polarimeter
Telescope area	2.6 m

QUaD is a ground-based polarimetric instrument designed to measure the polarization of the cosmic microwave background. Deployed at the Amundsen–Scott South Pole Station, the instrument aimed to probe anisotropy and polarization signals at degree and sub-degree angular scales to constrain models of inflation and large-scale structure. QUaD operated during the mid-2000s and produced maps and power spectra that informed analyses by teams associated with leading institutions and surveys.

Overview

QUaD was conceived to follow up on results from experiments such as COBE, WMAP, Boomerang (balloon), and DASI by improving angular resolution and sensitivity. The project built upon heritage from BICEP and the Degree Angular Scale Interferometer collaborations, and it worked in the context of complementary campaigns including Planck (spacecraft), SPT, and ACT (Atacama Cosmology Telescope). Scientific drivers included testing predictions from slow-roll inflation scenarios, constraining parameters related to cold dark matter, and searching for signatures associated with gravitational waves and reionization.

Instrumentation and Design

The QUaD instrument used a 2.6-meter classical Cassegrain telescope mounted within the Martin A. Pomerantz Observatory infrastructure at the South Pole, sharing logistical support with projects such as South Pole Telescope efforts. The focal plane housed an array of polarization-sensitive bolometers developed with technologies similar to those used by SCUBA and later by Planck HFI teams. QUaD observed in two frequency bands near 100 GHz and 150 GHz (roughly 3.2 mm and 2.0 mm) using feedhorn-coupled, polarization-selective detectors inspired by designs from BOOMERANG and MAXIMA programs. The cryogenic system drew on experience from DASI and CBI cryostats, maintaining bolometer temperatures with a closed-cycle refrigerator patterned after components used by Herschel and Spitzer instrument teams.

Optical design incorporated a reflective secondary and a rotatable half-wave plate mechanism comparable to hardware in Polarbear and CAPMAP experiments to modulate polarization signals and mitigate systematic effects such as instrumental polarization and ground pickup—issues previously characterized by COSMOSOMAS and QUaD contemporaries. Pointing and calibration strategies leveraged star camera techniques used by BOOMERanG and radio pointing methods similar to those at VLA.

Observations and Data Processing

Observing campaigns occurred primarily during austral winters from 2005 through 2007, coordinated with logistics agencies including United States Antarctic Program and personnel from University of Chicago and Princeton University. QUaD scanned selected low-foreground fields near the southern celestial pole, complementing sky coverage from WMAP and later Planck (spacecraft). Raw time-ordered data underwent preprocessing steps derived from pipelines developed in collaboration with groups from Stanford University and University of California, Berkeley, including deglitching, gain calibration against celestial sources like Jupiter (planet) and Centaurus A, and removal of atmospheric fluctuations guided by models used in SMA analyses.

Mapmaking employed maximum-likelihood estimators and pseudo-C_ell techniques adapted from methods introduced by MASTER (method), with Monte Carlo simulations similar to practices in BICEP and SPT analyses to estimate covariance, transfer functions, and bias correction. Polarization calibration referenced measurements of polarized astronomical sources and internal calibration loads; cross-correlation with maps from WMAP and surveys by IRAS and 2MASS helped characterize foreground contamination from synchrotron emission and dust emission as studied by teams including Planck Collaboration.

Scientific Results

QUaD produced high signal-to-noise measurements of the CMB temperature and polarization E-mode power spectra at angular scales corresponding to multipoles ℓ ~ 200–2000, providing complementary constraints to WMAP and later Planck (spacecraft) results. The data constrained parameters in ΛCDM frameworks and provided limits on tensor-to-scalar ratio parameters relevant to inflationary cosmology scenarios advanced by researchers at institutions like Harvard University and Caltech. QUaD also set upper limits on B-mode polarization at its targeted angular scales, informing strategies for future B-mode searches by collaborations such as BICEP2 and POLARBEAR. Analyses compared outcomes with theoretical predictions from codes maintained by the CAMB and CMBFAST communities and cross-validated power spectra with contemporaneous results from ACBAR and SZA.

Collaborations and Operations

The QUaD collaboration comprised scientists and engineers from universities and laboratories including Princeton University, University of Chicago, University of California, San Diego, and Rutgers University, coordinated with Antarctic logistics provided by British Antarctic Survey partners and the United States Antarctic Program. Funding and oversight involved agencies such as the National Science Foundation and collaborations with technical groups experienced from projects like BICEP and SPT. Operations adopted observing strategies, data management, and publication practices modeled on partnerships exemplified by Planck Collaboration and DASI consortia.

Legacy and Impact

Although operational for a relatively brief period, QUaD influenced instrument design and analysis techniques used in later experiments including BICEP2, SPTpol, and POLARBEAR. QUaD’s datasets and methodological developments informed component separation approaches later employed by the Planck Collaboration and parameter estimation pipelines used by teams at Kavli Institute for Cosmological Physics and Perimeter Institute. Its limits on B-mode polarization helped guide detector sensitivity and systematic control requirements for next-generation projects such as CMB-S4 and motivated continued investment from agencies including the European Southern Observatory and the National Science Foundation.

Category:Cosmic microwave background experiments