Helium surface fluctuations investigated with superconducting coplanar waveguide resonator

TL;DR

This study explores helium surface fluctuations by analyzing their impact on superconducting coplanar waveguide resonator frequency stability, revealing significant noise contributions from cryocooler-induced vibrations affecting quantum coherence.

Contribution

It introduces a method to quantify helium surface fluctuations via CPW resonator frequency shifts and compares these with accelerometer data, highlighting cryocooler vibrations as a major noise source.

Findings

Helium surface fluctuations cause measurable shifts in resonator frequency.

Cryocooler vibrations significantly contribute to resonator noise.

Surface fluctuation noise correlates with accelerometer measurements.

Abstract

Recent experiments on the coupling of the in-plane motional state of electrons floating on the surface of liquid helium to a microwave resonator have revealed the importance of helium surface fluctuations to the coherence of this motion. Here we investigate these surface fluctuations by studying the resonance properties of a superconducting coplanar waveguide (CPW) resonator filled with superfluid helium, where a significant fraction of the resonator's electromagnetic mode volume is coupled to the surface dynamics of the liquid. We present preliminary results on real-time CPW resonator frequency shifts driven by helium fluctuations, which are quantified via their power spectral density and compared with measurements using a commercial accelerometer. We find that a considerable contribution to the CPW resonator noise originates from the mechanical vibrations of the helium surface generated by the pulse tube (PT) cryocooler on the cryostat on which the experiments were performed.