Transformed Dissipation in Superconducting Quantum Circuits

TL;DR

This paper introduces a current transformation concept to quantify and mitigate environmental dissipation in superconducting quantum circuits, validated through experiments and theoretical calculations, improving qubit lifetime understanding.

Contribution

It presents a novel current transformation framework for analyzing dissipation in superconducting circuits, supported by experimental validation and quantum fluctuation analysis.

Findings

Impedance transformation of ~10^5 achieved

Quantitative agreement within a factor of 2 for qubit lifetime reduction

Higher-order quantum fluctuation effects do not limit qubit lifetime

Abstract

Superconducting quantum circuits must be designed carefully to avoid dissipation from coupling to external control circuitry. Here we introduce the concept of current transformation to quantify coupling to the environment. We test this theory with an experimentally-determined impedance transformation of $\sim 10^5$ and find quantitative agreement better than a factor of 2 between this transformation and the reduced lifetime of a phase qubit coupled to a tunable transformer. Higher-order corrections from quantum fluctuations are also calculated with this theory, but found not to limit the qubit lifetime. We also illustrate how this simple connection between current and impedance transformation can be used to rule out dissipation sources in experimental qubit systems.