---
title: "High-fidelity flopping-mode single-spin operation via triple-dot orbital-band engineering"
description: "Abstract Fast electrical spin rotations in quantum dots require strong spin-charge hybridization, but the same hybridization can increase sensitivity to detuning noise. In a double-quantum-dot (DQD) flopping-mode qubit, the sweet-spot width and the Rabi enhancement are both tied to the same orbital splitting…"
datePublished: "2026-10-24"
lastmod: "2026-10-27T12:39:04+00:00"
authors:
  - "Y. Matsumoto"
  - "X.-F. Liu"
  - "A. Ludwig"
  - "A. D. Wieck"
  - "K. Koike"
  - "T. Miyoshi"
  - "T. Fujita"
  - "A. Oiwa"
journal: "npj Quantum Information"
publisher: "Springer Science and Business Media LLC"
doi: "10.1038/s41534-026-01400-1"
publicationType: "journal-article"
schemaType: "ScholarlyArticle"
license: "https://creativecommons.org/licenses/by/4.0"
sponsor: "BMBF Q.Link.X; KAKENHI"
language: "en-GB"
slug: "10.1038-s41534-026-01400-1"
---

# High-fidelity flopping-mode single-spin operation via triple-dot orbital-band engineering

**Authors:** Y. Matsumoto, X.-F. Liu, A. Ludwig, A. D. Wieck, K. Koike, T. Miyoshi, T. Fujita, A. Oiwa  
**Journal:** npj Quantum Information  
**Publisher:** Springer Science and Business Media LLC  
**Published:** 2026-10-24  
**DOI:** [10.1038/s41534-026-01400-1](https://dx.doi.org/10.1038/s41534-026-01400-1)

## Abstract

Abstract Fast electrical spin rotations in quantum dots require strong spin-charge hybridization, but the same hybridization can increase sensitivity to detuning noise. In a double-quantum-dot (DQD) flopping-mode qubit, the sweet-spot width and the Rabi enhancement are both tied to the same orbital splitting, limiting post-fabrication optimization of the speed-coherence trade-off. Here, we demonstrate a GaAs triple-quantum-dot (TQD) flopping-mode qubit in which the detuning of the third dot, ϵ 34 , provides an additional electrical tuning parameter for orbital-band flattening. Tuning ϵ 34 flattens the qubit-frequency dependence on the detuning of the target DQD while maintaining strong spin-charge hybridization, enabling electrically driven Rabi frequencies above 100 MHz. We then use feedforward-neural-network (FNN) feedback to track slow qubit-frequency drift and connect this engineered operating point to high-fidelity gates. This feedback suppresses slow qubit-frequency fluctuations, reducing their standard deviation to 388 kHz, and yields a π /2 gate fidelity of 99.56% with a 4.05 ns gate time. These results identify TQD orbital-band engineering as an electrical route for tuning the speed-coherence trade-off, complementary to material-intrinsic spin-orbit coupling and fixed micromagnet geometry.

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