[Paper Review] Measuring the Cosmic Microwave Background Radiation (CMBR) polarization with QUIET

Dorothea Franziska Elisabeth Samtleben|arXiv (Cornell University)|Feb 19, 2008

Cosmology and Gravitation Theories18 citations

TL;DR

QUIET proposes a ground-based CMB polarization experiment using coherent HEMT-based receiver arrays at 90 GHz and 40 GHz to measure E- and B-mode anisotropies with high sensitivity and systematics control. By leveraging dual-frequency observations, array scaling to 1000 elements, and simultaneous Q/U measurement, QUIET aims to constrain the tensor-to-scalar ratio r to ~10⁻², probing inflationary physics near the GUT scale.

ABSTRACT

A major goal of upcoming experiments measuring the Cosmic Microwave Background Radiation (CMBR) is to reveal the subtle signature of inflation in the polarization pattern which requires unprecedented sensitivity and control of systematics. Since the sensitivity of single receivers has reached fundamental limits future experiments will take advantage of large receiver arrays in order to significantly increase the sensitivity. Here we introduce the Q/U Imaging ExperimenT (QUIET) which will use HEMT-based receivers in chip packages at 90(40) GHz in the Atacama Desert. Data taking is planned for the beginning of 2008 with prototype arrays of 91(19) receivers, an expansion to 1000 receivers is foreseen. With the two frequencies and a careful choice of scan regions there is the promise of effectively dealing with foregrounds and reaching a sensitivity approaching 10$^{-2}$ for the ratio of the tensor to scalar perturbations.

Motivation & Objective

• To measure the cosmic microwave background (CMB) polarization with unprecedented sensitivity and control of systematics to detect the inflationary B-mode signal.
• To achieve a sensitivity approaching r ≈ 10⁻², corresponding to GUT-scale inflation, by combining high-frequency (90 GHz) and low-frequency (40 GHz) observations.
• To develop and deploy large-scale coherent receiver arrays using chip-integrated pseudo-correlation radiometers to overcome sensitivity limits of single receivers.
• To minimize systematics through simultaneous Q and U Stokes parameter measurement, fast phase switching, and null-data monitoring.
• To complement Planck and bolometric experiments by using coherent detectors and enabling multi-scale angular resolution with different telescope sizes.

Proposed method

• Utilizes HEMT-based pseudo-correlation radiometers in compact chip packages for both 90 GHz (W-band) and 40 GHz (Q-band) frequencies.
• Employs a dual-frequency observing strategy to distinguish and subtract Galactic foregrounds (synchrotron and dust) from the primordial CMB signal.
• Deploys prototype arrays of 91 (90 GHz) and 19 (40 GHz) receivers on 1.4 m telescopes in the Atacama Desert, with plans to expand to 1000 elements.
• Uses orthomode transducers (OMTs) and feedhorns to separate orthogonal polarization states, feeding signals into MMIC-based radiometers on chip.
• Applies fast (4 kHz) phase switching to mitigate 1/f amplifier drifts and enables digital backend processing with in-phase and out-of-phase demodulation for systematic error detection.
• Mounts receivers in cryostats at 20 K to minimize HEMT noise, achieving target noise temperatures of 45 K (90 GHz) and 20 K (40 GHz).

Experimental results

Research questions

• RQ1 Can coherent HEMT-based receiver arrays achieve the sensitivity and systematics control required to detect primordial B-mode polarization at levels near r ≈ 10⁻²?
• RQ2 How effectively can dual-frequency observations (90/40 GHz) suppress Galactic foreground contamination in CMB polarization measurements?
• RQ3 To what extent does simultaneous Q and U measurement improve systematic error monitoring and calibration in CMB experiments?
• RQ4 What is the expected sensitivity of QUIET to the tensor-to-scalar ratio r, and how does it compare to Planck and other experiments?
• RQ5 Can array scaling to 1000 elements combined with multi-scale telescope deployment significantly enhance angular resolution and signal-to-noise for B-mode detection?

Key findings

• QUIET Phase I with 91 (90 GHz) and 19 (40 GHz) receivers is expected to measure the E-mode power spectrum with unprecedented precision, consistent with the ΛCDM model.
• The expected white noise level for QUIET maps is about one order of magnitude lower than Planck’s, due to higher sensitivity from ground-based arrays.
• With 1000-element arrays in Phase II, QUIET can constrain the tensor-to-scalar ratio r to a 5σ upper limit of 0.009, approaching the target sensitivity for GUT-scale inflation.
• Adding QUIET Phase I data to WMAP improves constraints on cosmological parameters to a level competitive with Planck’s expected precision, particularly for r and τ.
• QUIET’s use of coherent detectors and simultaneous Q/U measurement provides unique systematics monitoring capabilities not available in bolometric experiments.
• The experiment is designed to measure both large-scale (l ≈ 100) and small-scale (sub-degree) features using different telescope sizes, enhancing angular dynamic range.