Improved superconducting qubit coherence using titanium nitride

TL;DR

This paper reports a significant enhancement in superconducting qubit coherence times by using titanium nitride for capacitors, indicating surface losses from TLS defects as a key limiting factor.

Contribution

It introduces TiN-fabricated capacitors for transmon qubits, achieving up to six times longer coherence times and providing evidence of surface loss limitations.

Findings

Up to ~60 μs relaxation and dephasing times achieved

Six-fold improvement over previous aluminum-based qubits

Anomalous temperature-dependent frequency shift observed in TiN resonators

Abstract

We demonstrate enhanced relaxation and dephasing times of transmon qubits, up to ~ 60 \mu s by fabricating the interdigitated shunting capacitors using titanium nitride (TiN). Compared to lift-off aluminum deposited simultaneously with the Josephson junction, this represents as much as a six-fold improvement and provides evidence that previous planar transmon coherence times are limited by surface losses from two-level system (TLS) defects residing at or near interfaces. Concurrently, we observe an anomalous temperature dependent frequency shift of TiN resonators which is inconsistent with the predicted TLS model.