Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architecture

TL;DR

This paper demonstrates that a three-dimensional circuit QED architecture significantly enhances the coherence and stability of Josephson junction qubits, indicating promising prospects for scalable quantum computing.

Contribution

Introduction of a 3D resonator architecture that reduces decoherence and improves coherence times of Josephson junction qubits without additional noise suppression techniques.

Findings

Qubit coherence times of 10-20 microseconds without spin echo.

No evidence of 1/f critical current noise.

Potential for error rates near the quantum error correction threshold.

Abstract

Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether superconducting qubits can be adequately isolated from their environment. We introduce a new architecture for superconducting quantum circuits employing a three dimensional resonator that suppresses qubit decoherence while maintaining sufficient coupling to the control signal. With the new architecture, we demonstrate that Josephson junction qubits are highly coherent, with $T_2 \sim 10 \mu$s to $20 \mu$s without the use of spin echo, and highly stable, showing no evidence for $1/f$ critical current noise. These results suggest that the overall quality of Josephson junctions in these qubits will allow error rates of a few $10^{-4}$, approaching the error correction threshold.