Frequency Fluctuation of Transmon from a Charged Two-level System: Part II

The coupling of superconducting qubits to microscopic two-level system (TLS) is a prominent decoherence channel. Understanding the nature and the property of TLS is important to improve qubit coherence. In part II, we perform real-time joint tracking of TLS transitions and quasiparticle tunneling, and eliminate complex dynamics due to the non-QNDness of the transmon readout. We find no intrinsic correlation between quasiparticle and TLS dynamics, and measure a quasiparticle lifetime exceeding 6 ms and TLS relaxation time exceeding 3 ms. We further apply additional radiation and find the TLS relaxation unaffected.