The SPTpol camera is a two-color, polarization-sensitive bolometer receiver, and was installed on the 10 meter South Pole Telescope in January 2012. SPTpol is designed to study the faint polarization signals in the Cosmic Microwave Background, with two primary scientific goals. One is to constrain the tensor-to-scalar ratio of perturbations in the primordial plasma, and thus constrain the space of permissible in inflationary models. The other is to measure the weak lensing effect of large-scale structure on CMB polarization, which can be used to constrain the sum of neutrino masses as well as other growth-related parameters. The SPTpol focal plane consists of seven 84-element monolithic arrays of 150 GHz pixels (588 total) and 180 individual 90 GHz single- pixel modules. In this paper we present the design and characterization of the 90 GHz modules.
The SPTpol camera is a dichroic polarimetric receiver at 90 and 150 GHz. Deployed in January 2012 on the South Pole Telescope (SPT), SPTpol is looking for faint polarization signals in the Cosmic Microwave Background (CMB). The camera consists of 180 individual Transition Edge Sensor (TES) polarimeters at 90 GHz and seven 84-polarimeter camera modules (a total of 588 polarimeters) at 150 GHz. We present the design, dark characterization, and in-lab optical properties of the 150 GHz camera modules. The modules consist of photolithographed arrays of TES polarimeters coupled to silicon platelet arrays of corrugated feedhorns, both of which are fabricated at NIST-Boulder. In addition to mounting hardware and RF shielding, each module also contains a set of passive readout electronics for digital frequency-domain multiplexing. A single module, therefore, is fully functional as a miniature focal plane and can be tested independently. Across the modules tested before deployment, the detectors average a critical temperature of 478 mK, normal resistance RN of 1.2Ω , unloaded saturation power of 22.5 pW, (detector-only) optical efficiency of ~ 90%, and have electrothermal time constants < 1 ms in transition.
SPTpol is a dual-frequency polarization-sensitive camera that was deployed on the 10-meter South Pole Telescope in January 2012. SPTpol will measure the polarization anisotropy of the cosmic microwave background (CMB) on angular scales spanning an arcminute to several degrees. The polarization sensitivity of SPTpol will enable a detection of the CMB “B-mode” polarization from the detection of the gravitational lensing of the CMB by large scale structure, and a detection or improved upper limit on a primordial signal due to inationary gravity waves. The two measurements can be used to constrain the sum of the neutrino masses and the energy scale of ination. These science goals can be achieved through the polarization sensitivity of the SPTpol camera and careful control of systematics. The SPTpol camera consists of 768 pixels, each containing two transition-edge sensor (TES) bolometers coupled to orthogonal polarizations, and a total of 1536 bolometers. The pixels are sensitive to light in one of two frequency bands centered at 90 and 150 GHz, with 180 pixels at 90 GHz and 588 pixels at 150 GHz. The SPTpol design has several features designed to control polarization systematics, including: singlemoded feedhorns with low cross-polarization, bolometer pairs well-matched to dfference atmospheric signals, an improved ground shield design based on far-sidelobe measurements of the SPT, and a small beam to reduce temperature to polarization leakage. We present an overview of the SPTpol instrument design, project status, and science projections.
In January 2012, the 10m South Pole Telescope (SPT) was equipped with a polarization-sensitive camera, SPTpol, in order to measure the polarization anisotropy of the cosmic microwave background (CMB). Measurements of the polarization of the CMB at small angular scales (~several arcminutes) can detect the gravitational lensing of the CMB by large scale structure and constrain the sum of the neutrino masses. At large angular scales (~few degrees) CMB measurements can constrain the energy scale of Inflation. SPTpol is a two-color mm-wave camera that consists of 180 polarimeters at 90 GHz and 588 polarimeters at 150 GHz, with each polarimeter consisting of a dual transition edge sensor (TES) bolometers. The full complement of 150 GHz detectors consists of 7 arrays of 84 ortho-mode transducers (OMTs) that are stripline coupled to two TES detectors per OMT, developed by the TRUCE collaboration and fabricated at NIST. Each 90 GHz pixel consists of two antenna-coupled absorbers coupled to two TES detectors, developed with Argonne National Labs. The 1536 total detectors are read out with digital frequency-domain multiplexing (DfMUX). The SPTpol deployment represents the first on-sky tests of both of these detector technologies, and is one of the first deployed instruments using DfMUX readout technology. We present the details of the design, commissioning, deployment, on-sky optical characterization and detector performance of the complete SPTpol focal plane.
We present the software system used to control and operate the South Pole Telescope. The South Pole Telescope is
a 10-meter millimeter-wavelength telescope designed to measure anisotropies in the cosmic microwave background
(CMB) at arcminute angular resolution. In the austral summer of 2011/12, the SPT was equipped with a new
polarization-sensitive camera, which consists of 1536 transition-edge sensor bolometers. The bolometers are read
out using 36 independent digital frequency multiplexing (DfMux) readout boards, each with its own embedded
processors. These autonomous boards control and read out data from the focal plane with on-board software
and firmware. An overall control software system running on a separate control computer controls the DfMux
boards, the cryostat and all other aspects of telescope operation. This control software collects and monitors
data in real-time, and stores the data to disk for transfer to the United States for analysis.
Next generation cosmic microwave background (CMB) polarization anisotropy measurements will feature focal
plane arrays with more than 600 millimeter-wave detectors. We make use of high-resolution photolithography
and wafer-scale etch tools to build planar arrays of corrugated platelet feeds in silicon with highly symmetric
beams, low cross-polarization and low side lobes. A compact Au-plated corrugated Si feed designed for 150 GHz
operation exhibited performance equivalent to that of electroformed feeds: ~ -0.2 dB insertion loss, < -20 dB
return loss from 120 GHz to 170 GHz, < -25 dB side lobes and < -23 dB cross-polarization. We are currently
fabricating a 50mm diameter array with 84 horns consisting of 33 Si platelets as a prototype for the SPTpol and
ACTpol telescopes. Our fabrication facilities permit arrays up to 150mm in diameter.
The next generation of Cosmic Microwave Background (CMB) experiments probing for signals of inflation and
small angular scale polarization anisotropies require higher sensitivity and better control of systematics. We are
developing monolithic arrays of orthomode transducer (OMT) coupled transition edge sensor (TES) polarimeters
designed for operation at 150 GHz to address these requirements. OMT coupling allows for simultaneous and
independent detection of two orthogonal linear polarization states incident on a single pixel. We present measurements
of optical efficiencies ηop of single pixels with on-chip band-defining filters, with ηop = 57±4 stat±9 sys %.
We also provide evidence for an out-of-band blue leak and address possible sources as well as mitigation techniques.
Additionally, we discuss methods for increasing efficiency being implemented in the next generation of
pixels, currently in fabrication. Still under development, these pixels are produced as monolithic polarimeter arrays
and are slated for use in the Atacama Cosmology Telescope Polarization (ACTpol) and South Pole Telescope
Polarization (SPTpol) experiments, while single-pixel polarimeters are to be deployed in the Atacama B-mode
Search (ABS) experiment.
The six-meter Atacama Cosmology Telescope (ACT) in Chile was built to measure the cosmic microwave background
(CMB) at arcminute angular scales. We are building a new polarization sensitive receiver for ACT
(ACTPol). ACTPol will characterize the gravitational lensing of the CMB and aims to constrain the sum of the
neutrino masses with ~ 0.05 eV precision, the running of the spectral index of inflation-induced fluctuations,
and the primordial helium abundance to better than 1 %. Our observing fields will overlap with the SDSS BOSS
survey at optical wavelengths, enabling a variety of cross-correlation science, including studies of the growth of
cosmic structure from Sunyaev-Zel'dovich observations of clusters of galaxies as well as independent constraints
on the sum of the neutrino masses. We describe the science objectives and the initial receiver design.
Atomic ions confined in segmented trap arrays provide a system for quantum information processing. We
report on the execution of two simple quantum algorithms, quantum error correction and the quantum Fourier
transform, using this implementation. The demonstration of these algorithms in a scalable system is one step
towards the execution of useful, large-scale quantum algorithms.