Probing Two-Level Fluctuators Using a Dynamically Decoupled Qubit*

Two-level charge fluctuators (TLFs) plague all solid-state qubit devices, and identifying their switching rates and coupling strengths can shed light on their origin, paving the way to better device design and/or qubit working protocols to mitigate their adverse effects. This work introduces dynamical decoupling protocols that are designed to reconstruct charge fluctuator parameters. Using taylored sets of Mixed Concatenated Dynamically Decoupling sequences we show that the parameters of a  single TLF can be reconstructed with high fidelity over a wide range of coupling strengths. Our protocols are robust against substantial measurement errors and can be extended to consistently identify multiple TLFs, as long as their coupling strengths are within the same order of magnitude. These results suggest that our procedure could be a useful tool for identifying and characterizing TLFs in various solid-state qubit devices.