Coherent Josephson qubit suitable for scalable quantum integrated circuits

TL;DR

This paper presents a tunable superconducting Xmon qubit with coherence times up to 44 microseconds, achieved through geometry optimization to minimize losses and defects, advancing scalable quantum computing.

Contribution

The authors demonstrate a planar, tunable superconducting qubit with significantly improved coherence times and analyze the effects of material defects on qubit performance.

Findings

Coherence times up to 44 microseconds achieved

Geometry design reduces radiative loss and defect coupling

Presence of weakly coupled two-level defects identified

Abstract

We demonstrate a planar, tunable superconducting qubit with energy relaxation times up to 44 microseconds. This is achieved by using a geometry designed to both minimize radiative loss and reduce coupling to materials-related defects. At these levels of coherence, we find a fine structure in the qubit energy lifetime as a function of frequency, indicating the presence of a sparse population of incoherent, weakly coupled two-level defects. This is supported by a model analysis as well as experimental variations in the geometry. Our `Xmon' qubit combines facile fabrication, straightforward connectivity, fast control, and long coherence, opening a viable route to constructing a chip-based quantum computer.