Improving qubit coherence using closed-loop feedback

TL;DR

This paper demonstrates that closed-loop feedback can significantly enhance superconducting qubit coherence times and reduce error rates, enabling more stable and high-fidelity quantum operations over a broader frequency range.

Contribution

The study introduces an experimental method of using closed-loop feedback to stabilize qubit frequency fluctuations, improving coherence and fidelity beyond previous techniques.

Findings

Coherence time increased by 26%

Single-qubit error rate reduced from 8.5e-4 to 5.9e-4

High-fidelity operation effective over wider frequency range

Abstract

Superconducting qubits are a promising platform for building a larger-scale quantum processor capable of solving otherwise intractable problems. In order for the processor to reach practical viability, the gate errors need to be further suppressed and remain stable for extended periods of time. With recent advances in qubit control, both single- and two-qubit gate fidelities are now in many cases limited by the coherence times of the qubits. Here we experimentally employ closed-loop feedback to stabilize the frequency fluctuations of a superconducting transmon qubit, thereby increasing its coherence time by 26\% and reducing the single-qubit error rate from $(8.5 \pm 2.1)\times 10^{-4}$ to $(5.9 \pm 0.7)\times 10^{-4}$. Importantly, the resulting high-fidelity operation remains effective even away from the qubit flux-noise insensitive point, significantly increasing the frequency bandwidth over which the qubit can be operated with high fidelity. This approach is helpful in large qubit grids, where frequency crowding and parasitic interactions between the qubits limit their performance.