Non-local electrodynamics of superconducting wires: implications for flux noise and inductance
Date
2017-12-22
Authors
Senarath Yapa Arachchige, Pramodh Viduranga
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Abstract
The simplest model for superconductor electrodynamics are the London equations,
which treats the impact of electromagnetic fields on the current density as a localized
phenomenon. However, the charge carriers of superconductivity are quantum mechanical
objects, and their wavefunctions are delocalized within the superconductor,
leading to non-local effects. The Pippard equation is the generalization of London
electrodynamics which incorporates this intrinsic non-locality through the introduction
of a new superconducting characteristic length, \xi_0, called the Pippard coherence
length. When building nano-scale superconducting devices, the inclusion of the coherence
length into electrodynamics calculations becomes paramount. In this thesis, we
provide numerical calculations of various electrodynamic quantities of interest in the
non-local regime, and discuss their implications for building superconducting devices.
We place special emphasis on Superconducting QUantum Inteference Devices
(SQUIDs), and their usage as flux quantum bits (qubits) in quantum computation.
One of the main limitations of these flux qubits is the presence of intrinsic flux noise, which leads to decoherence of the qubits. Although the origin of this flux noise is not known, there is evidence that it is related to spin impurities within the superconducting
material. We present calculations which show that the flux noise in the
non-local regime is signi cantly different from the local case. We also demonstrate
that non-local electrodynamics greatly affect the self-inductance of the qubit.
Description
Keywords
superconductivity, quantum computing, qubit, flux noise, electrodynamics, SQUID, Superconductor, Pippard, non-local electrodynamics, inductance