Impact of Nonlocal Electrodynamics on the Flux Noise and Inductance of Superconducting Wires

Abstract

We present exact numerical calculations of the supercurrent density, inductance, and impurity-induced flux noise of cylindrical superconducting wires in the nonlocal Pippard regime, which occurs when the Pippard coherence length is greater than the London penetration depth. In this regime, the supercurrent density displays a peak away from the surface and changes sign inside the superconductor, signaling a breakdown of the usual approximation of local London electrodynamics with a renormalized penetration depth. Our calculations show that the internal inductance and the bulk flux noise power are enhanced in nonlocal superconductors. In contrast, the kinetic inductance is reduced and the surface flux noise remains the same. As a result, impurity spins in the bulk may dominate the flux noise in superconducting qubits in the Pippard regime, such as the ones using aluminum superconductors with a large electron mean free path.

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