Long-lived, radiation-suppressed superconducting quantum bit in a planar geometry

TL;DR

This paper introduces a planar superconducting qubit design with a superconducting ground plane that significantly enhances qubit lifetime by suppressing radiation loss, demonstrating improved coherence times.

Contribution

The work presents a novel 2D superconducting qubit architecture with a ground plane that reduces radiation loss, leading to longer qubit coherence times compared to traditional designs.

Findings

Qubit relaxation time (T1) of 11.7 microseconds

Qubit coherence time (T2) of 8.7 microseconds

Projections of increased T1 with reduced qubit-plane separation

Abstract

We present a superconducting qubit design that is fabricated in a 2D geometry over a superconducting ground plane to enhance the lifetime. The qubit is coupled to a microstrip resonator for readout. The circuit is fabricated on a silicon substrate using low loss, stoichiometric titanium nitride for capacitor pads and small, shadow-evaporated aluminum/aluminum-oxide junctions. We observe qubit relaxation and coherence times ($T_1$ and $T_2$) of 11.7 $\pm$ 0.2 $\mu$s and 8.7 $\pm$ 0.3 $\mu$s, respectively. Calculations show that the proximity of the superconducting plane suppresses the otherwise high radiation loss of the qubit. A significant increase in $T_1$ is projected for a reduced qubit-to-superconducting plane separation.