SLAC Microresonator Radio Frequency (SMuRF) Electronics for Read Out of Frequency-Division-Multiplexed Cryogenic Sensors

TL;DR

This paper introduces SMuRF electronics, a scalable control system for superconducting microresonator arrays, featuring advanced tone tracking algorithms that enhance linearity, increase sensor multiplexing, and demonstrate effective noise performance.

Contribution

The work presents a novel SMuRF electronics system with specialized closed-loop tone tracking algorithms for superconducting microresonator readout, enabling higher multiplexing and improved system linearity.

Findings

Successful demonstration of closed-loop tone tracking on twelve resonators

Achieved multi-kHz tracking bandwidth with subdominant electronics noise

Enhanced dynamic range through overcoupled resonator designs

Abstract

Large arrays of cryogenic sensors for various imaging applications ranging across x-ray, gamma-ray, Cosmic Microwave Background (CMB), mm/sub-mm, as well as particle detection increasingly rely on superconducting microresonators for high multiplexing factors. These microresonators take the form of microwave SQUIDs that couple to Transition-Edge Sensors (TES) or Microwave Kinetic Inductance Detectors (MKIDs). In principle, such arrays can be read out with vastly scalable software-defined radio using suitable FPGAs, ADCs and DACs. In this work, we share plans and show initial results for SLAC Microresonator Radio Frequency (SMuRF) electronics, a next-generation control and readout system for superconducting microresonators. SMuRF electronics are unique in their implementation of specialized algorithms for closed-loop tone tracking, which consists of fast feedback and feedforward to each resonator's excitation parameters based on transmission measurements. Closed-loop tone tracking enables improved system linearity, a significant increase in sensor count per readout line, and the possibility of overcoupled resonator designs for enhanced dynamic range. Low-bandwidth prototype electronics were used to demonstrate closed-loop tone tracking on twelve 300-kHz-wide microwave SQUID resonators, spaced at $\sim$6 MHz with center frequencies $\sim$5-6 GHz. We achieve multi-kHz tracking bandwidth and demonstrate that the noise floor of the electronics is subdominant to the noise intrinsic in the multiplexer.