Recent Advances in Frequency-Multiplexed TES Readout: Vastly Reduced Parasitics and an Increase in Multiplexing Factor with sub-Kelvin SQUIDs

TL;DR

This paper discusses recent technological advances in frequency-multiplexed TES readout systems, enabling higher detector counts with reduced parasitics and complexity, crucial for next-generation CMB experiments like CMB-S4.

Contribution

The paper presents novel improvements in frequency-multiplexed TES readout, including eliminating 4 K electronics, reducing parasitic impedances, and increasing multiplexing factors.

Findings

Elimination of 4 K electronics simplifies the system.

Significant reduction in parasitic in-series impedances.

Increase in multiplexing factor enhances detector readout capacity.

Abstract

Cosmic microwave background (CMB) measurements are fundamentally limited by photon statistics. Therefore, ground-based CMB observatories have been increasing the number of detectors that are simultaneously observing the sky. Thanks to the advent of monolithically fabricated transition edge sensor (TES) arrays, the number of on-sky detectors has been increasing exponentially for over a decade. The next-generation experiment CMB-S4 will increase this detector count by more than an order of magnitude from the current state-of-the-art to ~500,000. The readout of such a huge number of exquisitely precise sub-Kelvin sensors is feasible using an existing technology: frequency-domain multiplexing (fMux). To further optimize this system and reduce complexity and cost, we have recently made significant advances including the elimination of 4 K electronics, a massive decrease of parasitic in-series impedances, and a significant increase in multiplexing factor.