Spectroscopy of a hidden two-level system environment using a fluxonium qubit with fast-flux tunability

Recent experiments on a granular aluminum (grAl) fluxonium qubit [1] have shown non-exponential relaxation dynamics spanning over tens of milliseconds,

when the qubit is stabilized in its excited / ground state via active feedback [2]. 

The observed behavior can be explained by the active heating / cooling of a hidden two-level system environment of unknown physical origin.

In order to mitigate this dominant relaxation channel for the qubit, it is essential to gain a better understanding of its origin. 

Here we present a method to perform spectrocopy of this hidden environment using a similar grAl fluxonium qubit placed in a coplanar waveguide architecture with an integrated fast-flux coil.

[1] Grünhaupt and Spiecker et al., Nat. Mater. 18, 816–819 (2019)

[2] Spiecker et al., arXiv:2204.00499 (2022)