Josephson junctions supply the nonlinear inductance element in superconducting qubits. In the widely used transmon configuration, where the junction is shunted by a large capacitor, the low charging energy minimizes the sensitivity of the qubit to charge noise while maintaining the necessary anharmonicity to qubit states. We report here low-frequency transport measurements on small standalone junctions and identically fabricated capacitively-shunted junctions that show two distinct features normally attributed to small capacitance junctions near zero bias: reduced switching currents and prominent finite resistance associated with phase diffusion in the current-voltage characteristic. Our transport data reveals the existence of phase fluctuations in transmons arising from intrinsic junction capacitance.
@article{arxiv.2405.19658,
title = {Transport signatures of phase fluctuations in superconducting qubits},
author = {Maxwell Wisne and Yanpei Deng and Hilal Cansizoglu and Cameron Kopas and Josh Mutus and Venkat Chandrasekhar},
journal= {arXiv preprint arXiv:2405.19658},
year = {2024}
}