Development of a broadband reflective T-filter for voltage biasing high-Q superconducting microwave cavities

TL;DR

This paper introduces a broadband reflective T-filter that allows high-voltage biasing of superconducting microwave cavities with minimal loss, enabling advanced quantum and mechanical system applications.

Contribution

The paper presents a novel quasi-lumped element T-filter design that achieves high isolation and preserves high Q-factors in superconducting cavities under large dc bias.

Findings

Insertion loss >20 dB in 3-10 GHz range

Q-factors exceeding 10^5 at 20 V bias

Suitable for qubit-coupled mechanical systems

Abstract

We present the design of a reflective stop-band filter based on quasi-lumped elements that can be utilized to introduce large dc and low-frequency voltage biases into a low-loss superconducting coplanar waveguide (CPW) cavity. Transmission measurements of the filter are seen to be in good agreement with simulations and demonstrate insertion losses greater than $20\,{\rm dB}$ in the range of ${\rm 3\,to\,10\,GHz}$. Moreover, transmission measurements of the CPW's fundamental mode demonstrate that loaded quality factors exceeding $10^5$ can be achieved with this design for dc voltages as large as ${\rm 20\,V}$ and for the cavity operated in the single-photon regime. This makes the design suitable for use in a number of applications including qubit-coupled mechanical systems and circuit QED.