Qubit relaxation from evanescent-wave Johnson noise

TL;DR

This paper calculates how electromagnetic noise from nearby metals causes decoherence in quantum bits, providing formulas to predict qubit lifetimes based on their proximity to metallic components.

Contribution

It introduces a non-local dielectric model to accurately compute evanescent-wave Johnson noise, resolving previous divergences at metal surfaces.

Findings

Decoherence rates depend on distance to metal surfaces.

Formulas for electric and magnetic noise-induced decoherence are provided.

Results constrain design of quantum devices near metallic elements.

Abstract

In many quantum computer architectures, the qubits are in close proximity to metallic device elements. Metals have a high density of photon modes, and the fields spill out of the bulk metal because of the evanescent-wave component. Thus thermal and quantum electromagnetic Johnson- type noise from metallic device elements can decohere nearby qubits. In this paper we use quantum electrodynamics to compute the strength of this evanescent-wave Johnson noise as a function of distance z from a metallic half-space. Previous treatments have shown unphysical divergences at z = 0. We remedy this by using a proper non-local dielectric function. Decoherence rates of local qubits are proportional to the magnitude of electric or magnetic correlation functions evaluated at the qubit position. We present formulas for the decoherence rates. These formulas serve as an important constraint on future device architectures.