Fast single-qubit gates for continuous dynamically decoupled systems

TL;DR

This paper introduces fast, high-fidelity single-qubit gates compatible with continuous dynamical decoupling, enhancing quantum system robustness against environmental noise, demonstrated on a superconducting circuit.

Contribution

It develops universal, fast single-qubit gates tailored for CDD qubits, a novel approach for improving quantum coherence in noisy environments.

Findings

Achieved fidelity of 0.9947 with the gates

Demonstrated applicability on a frequency-tunable superconducting circuit

Enhanced robustness against longitudinal noise

Abstract

Environmental noise that couples longitudinally to a quantum system dephases that system and can limit its coherence lifetime. Performance using quantum superposition in clocks, information processors, communication networks, and sensors depends on careful state and external field selection to lower sensitivity to longitudinal noise. In many cases time varying external control fields--such as the Hahn echo sequence originally developed for nuclear magnetic resonance applications--can passively correct for longitudinal errors. There also exist continuous versions of passive correction called continuous dynamical decoupling (CDD), or spin-locking depending on context. However, treating quantum systems under CDD as qubits has not been well explored. Here, we develop universal single-qubit gates that are ``fast'' relative to perturbative Rabi gates and applicable to any CDD qubit architecture. We demonstrate single-qubit gates with fidelity $\mathcal{F}=0.9947(1)$ on a frequency tunable CDD transmon superconducting circuit operated where it is strongly sensitive to longitudinal noise, thus establishing this technique as a potentially useful tool for operating qubits in applications requiring high fidelity under non-ideal conditions.