Analysis of RF Surface Loss in a Planar 2D Qubit

TL;DR

This paper investigates microwave surface losses in planar superconducting transmon qubits, proposing an asymptotic method to estimate RF losses based on surface oxide properties to improve qubit coherence times.

Contribution

It introduces a numerical approach and an asymptotic method for estimating surface losses in transmon qubits, highlighting the impact of surface oxide and interface properties.

Findings

Estimated limits of RF losses based on surface oxide properties

Proposed an asymptotic method for energy participation ratio

Identified key factors affecting qubit coherence times

Abstract

The Josephson junction and shunt capacitor form a transmon qubit, which is the cornerstone of modern quantum computing platforms. For reliable quantum computing, it is important how long a qubit can remain in a superposition of quantum states, which is determined by the coherence time (T1). The coherence time of a qubit effectively sets the "lifetime" of usable quantum information, determining how long quantum computations can be performed before errors occur and information is lost. There are several sources of decoherence in transmon qubits, but the predominant one is generally considered to be dielectric losses in the natural oxide layer formed on the surface of the superconductor. In this paper, we present a numerical study of microwave surface losses in planar superconducting antennas of different transmon qubit designs. An asymptotic method for estimating the energy participation ratio in ultrathin films of nanometer scales is proposed, and estimates are given for the limits of achievable minimum RF losses depending on the electrical properties of the surface oxide and the interface of the qubit with the substrate material.