Low Temperature Detectors for CMB Imaging Arrays

TL;DR

This paper reviews the development of low temperature detector arrays for CMB polarization imaging, highlighting current technology, challenges, and future fabrication prospects for large-scale deployment.

Contribution

It provides a comprehensive overview of detector architectures, compares ideal design criteria with current technology, and discusses fabrication challenges for next-generation CMB arrays.

Findings

Current arrays achieve many ideal features but lack full capabilities.

Existing superconducting circuits enable advanced CMB imaging.

Fabrication of large-scale arrays with ~10^6 sensors is feasible but challenging.

Abstract

We review advances in low temperature detector (LTD) arrays for Cosmic Microwave Background (CMB) polarization experiments, with a particular emphasis on imaging arrays. We briefly motivate the science case, which has spurred a large number of independent experimental efforts. We describe the challenges associated with CMB polarization measurements and how these challenges impact LTD design. Key aspects of an ideal CMB polarization imaging array are developed and compared to the current state-of-the-art. These aspects include dual-polarization-sensitivity, background-limited detection over a 10:1 bandwidth ratio, and frequency independent angular responses. Although existing technology lacks all of this capability, today's CMB imaging arrays achieve many of these ideals and are highly advanced superconducting integrated circuits. Deployed arrays map the sky with pixels that contain elements for beam formation, polarization diplexing, passband definition in multiple frequency channels, and bolometric sensing. Several detector architectures are presented. We comment on the implementation of both transition-edge-sensor bolometers and microwave kinetic inductance detectors for CMB applications. Lastly, we discuss fabrication capability in the context of next-generation instruments that call for $\sim 10^6$ sensors.