Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2609.33229 · Physical Review Applied

In-plane optimal qubit operation with control fidelities exceeding 99 %

Yu-Chen Zhou, Zhenzhen Kong, Rong-Long Ma, Hao-Tian Jiang, Ao-Ran Li, Yang Zhong, Zhi-Tao Wu, Rui Zheng, Gui-Lei Wang, Gang Cao, Hai-Ou Li, Guo-Ping Guo

quant-phcond-mat.mes-hallSubmitted Sep 27, 2026• Announced Sep 29, 2026• 0 citations
arXivHTMLPDF

Abstract

Hole spin qubits based on semiconductor quantum dots are promising for building future large-scale quantum computers owing to their all-electrical manipulation. However, abundant physical mechanisms of valence band holes lead to anisotropic qubit properties. There is an opportunity to prolong the coherence time and achieve high-fidelity qubit manipulations. Here, we report a single-hole spin qubit in a planar germanium quantum dot and investigate its anisotropic susceptibility to charge noise under an in-plane magnetic field. By correlating the longitudinal spin-electric susceptibility with qubit coherence and control performance, we identify an optimal operating point where the sensitivity to charge noise is minimized. We find that optimizing the magnetic-field orientation reduces the spin-electric susceptibility, resulting in a five-fold enhancement of the Hahn-echo coherence time and a nearly tenfold suppression of control infidelity. At the optimal operating point, gate set tomography demonstrates the maximum gate fidelity of 99.82 %. Our finding enhances the prospects of hole spin qubits for scalable quantum information processing.

Journal reference
Physical Review Applied 26, 044059 (2026)
DOI
10.1103/fw9y-ylsv
Comments
12 pages,6 figures,Accepted by Physical Review Applied

Related papers

Coherent and ultra-low-power EDSR with a flopping-mode spin qubit in germanium

Alexei Orekhov, Wonjin Jang, Pan Zhang +13 more

Hole spin qubits in semiconductor quantum dots (QDs) enable high-fidelity all-electric control, but conventional electric dipole spin resonance (EDSR) can require substantial rf drive power at the low magnetic fields that are favorable for qubit coherence and readout. In planar Ge hole spin qubits, this can reach -27 dBm at the device, posing challenges for scalable architectures due to heating and crosstalk. Here, we demonstrate a flopping-mode (FM) qubit in Ge, where a single spin is delocalized in a double QD, combining first-order protection against charge noise with exceptionally efficient electric driving. By mapping out coherence sweet-spots as a function of magnetic field orientation we achieve $T_2^*= 1.4μ\mathrm{s}$, $T_2^{\mathrm{Hahn}}= 11.5 μ\mathrm{s}$, $T^{φ, \mathrm{CPMG32}}_2= 130 μ\mathrm{s}$, and $T_1= 226 μ\mathrm{s}$, and a single-qubit gate fidelity of up to 99.76$\%$ for a gate time $t_{Xπ} = 88$ ns. Importantly, these results are obtained at a nearly in-plane magnetic field of 5 mT using only -52 dBm drive power at the device. We further find that qubit relaxation in this regime is consistent with a two-photon Orbach process, providing a route for further optimization. Our results demonstrate that FM-EDSR supports ultra-low-power, high-fidelity single-qubit operations, improvements that could benefit scalable hole-spin-based architectures and hybrid spin-photon interfaces.

cond-mat.mes-hallCross-listedarXiv:2609.20775•Sep 18, 2026

High-fidelity geometric quantum gates exceeding 99.9% in germanium quantum dots

Yu-Chen Zhou, Rong-Long Ma, Zhenzhen Kong +11 more

Achieving high-fidelity and robust qubit manipulations is a crucial requirement for realizing faulttolerant quantum computation. Here, we demonstrate a single-hole spin qubit in a germanium quantum dot and characterize its control fidelity using gate set tomography. The maximum control fidelities reach 97.48%, 99.81%, 99.88% for the I, X/2 and Y /2 gate, respectively. These results reveal that off-resonance noise during consecutive I gates in gate set tomography sequences severely limits qubit performance. Therefore, we introduce geometric quantum computation to realize noiseresilient qubit manipulation. The geometric gate control fidelities remain above 99% across a wide range of Rabi frequencies. The maximum fidelity surpasses 99.9%. Furthermore, the fidelities of geometric X/2 and Y /2 (I) gates exceed 99% even when detuning the microwave frequency by +-2.5 MHz (+-1.2 MHz), highlighting the noise-resilient feature. These results demonstrate that geometric quantum computation is a potential method for achieving high-fidelity qubit manipulation reproducibly in semiconductor quantum computation.

quant-pharXiv:2609.33251•Nature Communications•Sep 29, 2026•12 citations

Hole Spin Qubits in Thin Curved Quantum Wells

Stefano Bosco, Daniel Loss

Hole spin qubits are frontrunner platforms for scalable quantum computers because of their large spin-orbit interaction that enables ultrafast all-electric qubit control at low power. The fastest spin qubits to date are defined in long quantum dots with two tight confinement directions, when the driving field is aligned to the smooth direction. However, in these systems the lifetime of the qubit is strongly limited by charge noise, a major issue in hole qubits. We propose here a different, scalable qubit design, compatible with planar CMOS technology, where the hole is confined in a curved germanium quantum well surrounded by silicon. This design takes full advantage of the strong spin-orbit interaction of holes, and at the same time suppresses charge noise in a wide range of configurations, enabling highly coherent, ultrafast qubit gates. While here we focus on a $\mathrm{Si}$/$\mathrm{Ge}$/$\mathrm{Si}$ curved quantum well, our design is also applicable to different semiconductors. These devices allow for ultrafast operations even in short quantum dots by a transversal electric field. This additional driving mechanism relaxes the demanding design constraints, and offers a way to reliably interface spin qubits in a single quantum dot to microwave photons. By considering state-of-the-art high-impedance resonators and realistic qubit designs, we estimate interaction strengths of a few hundreds of megahertz, largely exceeding the decay rate of spins and photons. Reaching such a strong coupling regime in hole spin qubits will be a significant step towards high-fidelity entangling operations between distant qubits, as well as fast single-shot readout, and could pave the way towards the implementation of a large-scale semiconducting quantum processor.

arXiv:2204.08212•Physical Review Applied•Oct 14, 2022•25 citations

Noise-protected two-qubit gate using anisotropic exchange interaction

Zizheng Wu, Maximilian Rimbach-Russ

Hole spin qubits hosted in Germanium quantum dots are promising candidates for scalable quantum computing. The strong spin-orbit interaction can enable fast and all-electrical quantum control. Furthermore, the platform can implement universal quantum control using only baseband signals, which may mitigate the impact of crosstalk and microwave-induced heating. At the same time, spin-orbit interaction gives rise to an anisotropic exchange interaction, whose potential for implementing two-qubit gates has remained largely unexplored. However, the current performance of operating a hole-based quantum computer is mostly limited by dephasing due to low-frequency charge noise. In this work, we propose a novel two-qubit gate protocol for Germanium hole spin qubits operated in the gapless regime. This gate protocol exploits the anisotropic exchange interaction between neighboring spins and utilizes a composite pulse scheme implemented solely through electrical baseband signals. Using this approach, we predict high-fidelity two-qubit controlled-Z operations that can suppress exchange-energy fluctuations, offering a pathway toward fault-tolerant semiconductor quantum processors.

cond-mat.mes-hallCross-listedarXiv:2603.13039•Mar 16, 2026•0 citations

Noise-protected two-qubit gate using anisotropic exchange interaction

Zizheng Wu, Maximilian Rimbach-Russ

Hole spin qubits hosted in Germanium quantum dots are promising candidates for scalable quantum computing. The strong spin-orbit interaction can enable fast and all-electrical quantum control. Furthermore, the platform can implement universal quantum control using only baseband signals, which may mitigate the impact of crosstalk and microwave-induced heating. At the same time, spin-orbit interaction gives rise to an anisotropic exchange interaction, whose potential for implementing two-qubit gates has remained largely unexplored. However, the current performance of operating a hole-based quantum computer is mostly limited by dephasing due to low-frequency charge noise. In this work, we propose a novel two-qubit gate protocol for Germanium hole spin qubits operated in the gapless regime. This gate protocol exploits the anisotropic exchange interaction between neighboring spins and utilizes a composite pulse scheme implemented solely through electrical baseband signals. Using this approach, we predict high-fidelity two-qubit controlled-Z operations that can suppress exchange-energy fluctuations, offering a pathway toward fault-tolerant semiconductor quantum processors.

Physical Review Applied•Oct 21, 2026•0 citations

Electrically Tuneable Variability in Germanium Hole Spin Qubits

Edmondo Valvo, Michele Jakob, Patrick Del Vecchio +2 more

Hole spin qubits in planar germanium heterostructures are frontrunners for scalable semiconductor quantum computing. However, their current performance is mostly limited by large dot-to-dot variability that leads to uncontrolled qubit energies and random tilts in the spin quantization axis. Here, we propose a systematic and local method to engineer the spin qubit response by imprinting a controlled anisotropy in the quantum dot confinement, enabling on-demand electric g-tensor control. In particular, we find that both the quantum-dot size and asymmetry allow electrical tuning of the g-tensor and significantly suppress magnitude and angular variability of the spin response for selected magnetic field directions. We confirm this behavior by analyzing single-disorder realizations and statistical ensembles in state-of-the-art strained and unstrained germanium channels, showing that the latter provides an optimal path for $g$-tensor engineering. Our results provide practical design principles for on-demand control of the spin response and mitigating variability, paving the way towards large-scale germanium-based quantum computers.

cond-mat.mes-hallCross-listedarXiv:2512.12702•Dec 16, 2025
Hole spin qubits based on semiconductor quantum dots are promising for building future large-scale quantum computers owing to their all-electrical manipulation. However, abundant physical mechanisms of valence band holes lead to anisotropic qubit properties. There is an opportunity to prolong the coherence time and achieve high-fidelity qubit manipulations. Here, we report a single-hole spin qubit in a planar germanium quantum dot and investigate its anisotropic susceptibility to charge noise under an in-plane magnetic field. By correlating the longitudinal spin-electric susceptibility with qubit coherence and control performance, we identify an optimal operating point where the sensitivity to charge noise is minimized. We find that optimizing the magnetic-field orientation reduces the spin-electric susceptibility, resulting in a five-fold enhancement of the Hahn-echo coherence time and a nearly tenfold suppression of control infidelity. At the optimal operating point, gate set tomography demonstrates the maximum gate fidelity of 99.82 %. Our finding enhances the prospects of hole spin qubits for scalable quantum information processing.
Hole spin qubits in semiconductor quantum dots (QDs) enable high-fidelity all-electric control, but conventional electric dipole spin resonance (EDSR) can require substantial rf drive power at the low magnetic fields that are favorable for qubit coherence and readout. In planar Ge hole spin qubits, this can reach -27 dBm at the device, posing challenges for scalable architectures due to heating and crosstalk. Here, we demonstrate a flopping-mode (FM) qubit in Ge, where a single spin is delocalized in a double QD, combining first-order protection against charge noise with exceptionally efficient electric driving. By mapping out coherence sweet-spots as a function of magnetic field orientation we achieve T2∗=1.4μsT_2^*= 1.4μ\mathrm{s}T2∗​=1.4μs, T2Hahn=11.5μsT_2^{\mathrm{Hahn}}= 11.5 μ\mathrm{s}T2Hahn​=11.5μs, T2φ,CPMG32=130μsT^{φ, \mathrm{CPMG32}}_2= 130 μ\mathrm{s}T2φ,CPMG32​=130μs, and T1=226μsT_1= 226 μ\mathrm{s}T1​=226μs, and a single-qubit gate fidelity of up to 99.76%\%% for a gate time tXπ=88t_{Xπ} = 88tXπ​=88 ns. Importantly, these results are obtained at a nearly in-plane magnetic field of 5 mT using only -52 dBm drive power at the device. We further find that qubit relaxation in this regime is consistent with a two-photon Orbach process, providing a route for further optimization. Our results demonstrate that FM-EDSR supports ultra-low-power, high-fidelity single-qubit operations, improvements that could benefit scalable hole-spin-based architectures and hybrid spin-photon interfaces.
Achieving high-fidelity and robust qubit manipulations is a crucial requirement for realizing faulttolerant quantum computation. Here, we demonstrate a single-hole spin qubit in a germanium quantum dot and characterize its control fidelity using gate set tomography. The maximum control fidelities reach 97.48%, 99.81%, 99.88% for the I, X/2 and Y /2 gate, respectively. These results reveal that off-resonance noise during consecutive I gates in gate set tomography sequences severely limits qubit performance. Therefore, we introduce geometric quantum computation to realize noiseresilient qubit manipulation. The geometric gate control fidelities remain above 99% across a wide range of Rabi frequencies. The maximum fidelity surpasses 99.9%. Furthermore, the fidelities of geometric X/2 and Y /2 (I) gates exceed 99% even when detuning the microwave frequency by +-2.5 MHz (+-1.2 MHz), highlighting the noise-resilient feature. These results demonstrate that geometric quantum computation is a potential method for achieving high-fidelity qubit manipulation reproducibly in semiconductor quantum computation.
Hole spin qubits are frontrunner platforms for scalable quantum computers because of their large spin-orbit interaction that enables ultrafast all-electric qubit control at low power. The fastest spin qubits to date are defined in long quantum dots with two tight confinement directions, when the driving field is aligned to the smooth direction. However, in these systems the lifetime of the qubit is strongly limited by charge noise, a major issue in hole qubits. We propose here a different, scalable qubit design, compatible with planar CMOS technology, where the hole is confined in a curved germanium quantum well surrounded by silicon. This design takes full advantage of the strong spin-orbit interaction of holes, and at the same time suppresses charge noise in a wide range of configurations, enabling highly coherent, ultrafast qubit gates. While here we focus on a Si\mathrm{Si}Si/Ge\mathrm{Ge}Ge/Si\mathrm{Si}Si curved quantum well, our design is also applicable to different semiconductors. These devices allow for ultrafast operations even in short quantum dots by a transversal electric field. This additional driving mechanism relaxes the demanding design constraints, and offers a way to reliably interface spin qubits in a single quantum dot to microwave photons. By considering state-of-the-art high-impedance resonators and realistic qubit designs, we estimate interaction strengths of a few hundreds of megahertz, largely exceeding the decay rate of spins and photons. Reaching such a strong coupling regime in hole spin qubits will be a significant step towards high-fidelity entangling operations between distant qubits, as well as fast single-shot readout, and could pave the way towards the implementation of a large-scale semiconducting quantum processor.
Hole spin qubits hosted in Germanium quantum dots are promising candidates for scalable quantum computing. The strong spin-orbit interaction can enable fast and all-electrical quantum control. Furthermore, the platform can implement universal quantum control using only baseband signals, which may mitigate the impact of crosstalk and microwave-induced heating. At the same time, spin-orbit interaction gives rise to an anisotropic exchange interaction, whose potential for implementing two-qubit gates has remained largely unexplored. However, the current performance of operating a hole-based quantum computer is mostly limited by dephasing due to low-frequency charge noise. In this work, we propose a novel two-qubit gate protocol for Germanium hole spin qubits operated in the gapless regime. This gate protocol exploits the anisotropic exchange interaction between neighboring spins and utilizes a composite pulse scheme implemented solely through electrical baseband signals. Using this approach, we predict high-fidelity two-qubit controlled-Z operations that can suppress exchange-energy fluctuations, offering a pathway toward fault-tolerant semiconductor quantum processors.
Hole spin qubits hosted in Germanium quantum dots are promising candidates for scalable quantum computing. The strong spin-orbit interaction can enable fast and all-electrical quantum control. Furthermore, the platform can implement universal quantum control using only baseband signals, which may mitigate the impact of crosstalk and microwave-induced heating. At the same time, spin-orbit interaction gives rise to an anisotropic exchange interaction, whose potential for implementing two-qubit gates has remained largely unexplored. However, the current performance of operating a hole-based quantum computer is mostly limited by dephasing due to low-frequency charge noise. In this work, we propose a novel two-qubit gate protocol for Germanium hole spin qubits operated in the gapless regime. This gate protocol exploits the anisotropic exchange interaction between neighboring spins and utilizes a composite pulse scheme implemented solely through electrical baseband signals. Using this approach, we predict high-fidelity two-qubit controlled-Z operations that can suppress exchange-energy fluctuations, offering a pathway toward fault-tolerant semiconductor quantum processors.
Hole spin qubits in planar germanium heterostructures are frontrunners for scalable semiconductor quantum computing. However, their current performance is mostly limited by large dot-to-dot variability that leads to uncontrolled qubit energies and random tilts in the spin quantization axis. Here, we propose a systematic and local method to engineer the spin qubit response by imprinting a controlled anisotropy in the quantum dot confinement, enabling on-demand electric g-tensor control. In particular, we find that both the quantum-dot size and asymmetry allow electrical tuning of the g-tensor and significantly suppress magnitude and angular variability of the spin response for selected magnetic field directions. We confirm this behavior by analyzing single-disorder realizations and statistical ensembles in state-of-the-art strained and unstrained germanium channels, showing that the latter provides an optimal path for ggg-tensor engineering. Our results provide practical design principles for on-demand control of the spin response and mitigating variability, paving the way towards large-scale germanium-based quantum computers.