F. Souris

Cryogenic Microwave Filter Cavity with a Tunability Greater than 5 GHz

  1. T.J. Clark,
  2. V. Vadakkumbatt,
  3. F. Souris,
  4. H. Ramp,
  5. and J.P. Davis
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 ∼500MHz. 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 ≈7×10^3 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.
arxiv pdf

Tuning a 3D Microwave Cavity via Superfluid Helium at MilliKelvin Temperatures

  1. F. Souris,
  2. H. Christiani,
  3. and J.P. Davis
Frequency tunability of 3D microwave cavities opens up numerous possibilities for their use in hybrid quantum systems and related technologies. For many applications it is desirable
to tune the resonance at cryogenic temperatures without mechanical actuation. We show that a superconducting 3D microwave cavity can be tuned at the percent level by taking advantage of the dielectric properties of superfluid 4He at milliKelvin temperatures, without affecting its intrinsic quality factor — reaching 3×105 in the present experiment.
arxiv pdf