Dynamical disorder of two-level defects in quantum devices

Quantum defects in the form of two-level systems (TLSs) are a dominant source of noise affecting relaxation and coherence of superconducting qubits. Long time modifications of the spectral properties are especially deleterious to scalability, since sweet spots frequencies for qubit coherence and relaxation vary in time and space. In this talk we present new experimental evidence for the existence of two types of TLSs, interacting weakly and strongly with the strain. We then argue that it is the dynamic disorder introduced by the strongly interacting TLSs that is responsible for the significant changes in the spectral properties of the TLS bath over thermal cycling, as well as over long times at low temperatures.