Cryogenic Microwave Filter Cavity with a Tunability Greater than 5 GHz

TL;DR

This paper presents a cryogenic superconducting microwave cavity with over 5 GHz tunability achieved by helium pressurization, maintaining a high quality factor and enabling improved phase noise filtering at low temperatures.

Contribution

The authors demonstrate a novel cryogenic tunable microwave cavity with greater than 5 GHz tuning range, surpassing previous limitations, and show its application in phase noise filtering.

Findings

Achieved >5 GHz tunability in a cryogenic superconducting cavity.

Maintained a consistent quality factor of approximately 7,000 across tuning range.

Reduced phase noise by about 10 dB above 400 kHz using the tunable filter.

Abstract

A wide variety of applications of microwave cavities, such as measurement and control of superconducting qubits, magnonic resonators, and phase noise filters, would be well served by having a highly tunable microwave resonance. Often this tunability is desired in situ at low temperatures, where one can take advantage of superconducting cavities. To date, such cryogenic tuning while maintaining a high quality factor has been limited to $\sim500$ MHz. Here we demonstrate a three-dimensional superconducting microwave cavity that shares one wall with a pressurized volume of helium. Upon pressurization of the helium chamber the microwave cavity is deformed, which results in in situ tuning of its resonant frequency by more than 5 GHz, greater than 60% of the original 8 GHz resonant frequency. The quality factor of the cavity remains approximately constant at $\approx7\times 10^{3}$ over the entire range of tuning. As a demonstration of its usefulness, we implement a tunable cryogenic phase noise filter, which reduces the phase noise of our source by approximately 10 dB above 400 kHz.