Cryogenic microwave filter cavity with a tunability greater than 5 GHz

Area of Science:

• Superconducting quantum devices
• Microwave engineering
• Low-temperature physics

Background:

• Tunable microwave resonators are crucial for applications like superconducting qubit control and magnonic devices.
• Existing cryogenic tuning methods for superconducting cavities are limited to approximately 500 MHz.
• Maintaining high quality factors during in situ tuning at low temperatures is a significant challenge.

Purpose of the Study:

• To demonstrate a novel three-dimensional superconducting microwave cavity with a wide range of in situ cryogenic tunability.
• To achieve frequency tuning exceeding 5 GHz while preserving a high quality factor.
• To showcase the utility of this tunable cavity in a practical application, such as a phase noise filter.

Main Methods:

• Designed a 3D superconducting microwave cavity sharing a wall with a pressurized helium volume.
• Utilized helium pressurization to deform the cavity and tune its resonant frequency.
• Measured the resonant frequency and quality factor across the tuning range.

Main Results:

• Achieved an in situ frequency tuning range of over 5 GHz (more than 60% of the original 8 GHz).
• Maintained a high and constant quality factor of approximately 7 × 10^3 throughout the tuning range.
• Demonstrated a tunable cryogenic phase noise filter that reduced source phase noise by ~10 dB above 400 kHz.

Conclusions:

• The developed superconducting microwave cavity offers unprecedented cryogenic tunability.
• This technology is well-suited for applications requiring in situ frequency adjustment at low temperatures.
• The tunable cavity significantly enhances the performance of cryogenic phase noise filters and opens new avenues for quantum technologies.