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Observation of Discrete Charge States of a Coherent Two-Level System in a Superconducting Qubit

Bao-Jie Liu, Ying-Ying Wang, Tal Sheffer, Chen Wang

DOI 10.1103/PhysRevLett.133.160602 · Physical Review Letters

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Abstract

We report observations of discrete charge states of a coherent two-level system (TLS) that is strongly coupled to an offset-charge-sensitive superconducting transmon qubit. We measure an offset charge of 0.072e associated with the two TLS eigenstates, which have a transition frequency of 2.9 GHz and a relaxation time exceeding 3 ms. Combining measurements in the strong dispersive and resonant regime, we quantify both transverse and longitudinal coupling of the TLS-qubit interaction. We further perform joint tracking of TLS transitions and quasiparticle tunneling dynamics but find no intrinsic correlations. This Letter demonstrates microwave-frequency TLS as a source of low-frequency charge noise.

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