Robust cryogenic matched low-pass coaxial filters for quantum computing applications

TL;DR

This paper presents the design, fabrication, and testing of robust, low-loss, matched low-pass coaxial filters operating up to 20 GHz, enhancing noise suppression in superconducting quantum circuits at milliKelvin temperatures.

Contribution

It introduces a universal design and assembly method for low-pass coaxial filters with predictable transmission properties, suitable for quantum computing applications.

Findings

Achieved a transmission coefficient with -1dB/GHz absorption

Demonstrated ultralow reflection losses below -20 dB up to 20 GHz

Validated the design with three nearly identical filters across 0-20 GHz

Abstract

Electromagnetic noise is one of the key external factors decreasing superconducting qubits coherence. Matched coaxial filters can prevent microwave and IR photons negative influence on superconducting quantum circuits. Here, we report on design and fabrication route of matched low-pass coaxial filters for noise-sensitive measurements at milliKelvin temperatures. A robust transmission coefficient with designed linear absorption (-1dB/GHz) and ultralow reflection losses less than -20 dB up to 20 GHz is achieved. We present a mathematical model for evaluating and predicting filters transmission parameters depending on their dimensions. It is experimentally approved on two filters prototypes different lengths with compound of Cu powder and Stycast commercial resin demonstrating excellent matching. The presented design and assembly route are universal for various compounds and provide high repeatability of geometrical and microwave characteristics. Finally, we demonstrate three filters with almost equal reflection and transmission characteristics in the range from 0 to 20 GHz, which is quite useful to control multiple channel superconducting quantum circuits.