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

Applied Physics Express

High-fidelity resonantly driven singlet–triplet qubit in SiMOS quantum dot at zero applied external magnetic field

Wei-Zhu Liao, Sheng-Kai Zhu, Ao-Ran Li, Zhen-Zhen Kong, Yi-Fan Lu, Ning Chu, Chu Wang, Guilei Wang, Gang Cao, Haiou Li, Guo-Ping Guo

Published Oct 1, 2026• 0 citations
Publisher

Abstract

We report a resonantly driven singlet–triplet (ST) qubit in a silicon metal–oxide–semiconductor (SiMOS) device operated without an applied external magnetic field. By resonantly modulating the exchange interaction at the qubit frequency, f q = 36 MHz , we observe coherent Rabi oscillations at f R = 1.69 MHz . A Ramsey measurement gives a dephasing time T 2 ∗ = 1.83 μ s , and randomized benchmarking yields an average single-qubit gate fidelity of 99.48%. These results demonstrate that the residual micromagnet field gradient is sufficient to support high-fidelity resonant control without a continuously applied external magnetic field.

DOI
10.35848/1882-0786/aeaf43

Related papers

A dressed singlet-triplet qubit in germanium

Konstantinos Tsoukalas, Uwe von Lüpke, Alexei Orekhov +15 more

Abstract In semiconductor hole spin qubits, low magnetic field ( B ) operation extends the coherence time ( $${T}_{2}^{*}$$ T 2 * ) but proportionally reduces the gate speed. In contrast, singlet-triplet (ST) qubits are primarily controlled by the exchange interaction ( J ) and can thus maintain high gate speeds even at low B . However, a large J introduces a significant charge component to the qubit, rendering ST qubits more vulnerable to charge noise when driven. Here, we demonstrate a highly coherent ST hole spin qubit in germanium, operating at both low B and low J . By modulating J , we achieve resonant driving of the ST qubit, obtaining an average gate fidelity of 99.68% and a coherence time of $${T}_{2}^{*}=1.9\,\mu {{{\rm{s}}}}$$ T 2 * = 1.9 μ s . Moreover, by applying the resonant drive continuously, we realize a dressed ST qubit with a tenfold increase in coherence time ( $${T}_{2\rho }^{*}=20.3\,\mu {{{\rm{s}}}}$$ T 2 ρ * = 20.3 μ s ). Frequency modulation of the driving signal enables universal control, with an average gate fidelity of 99.63%. Our results demonstrate the potential for extending coherence times while preserving high-fidelity control of germanium-based ST qubits, paving the way for more efficient operations in semiconductor-based quantum processors.

arXiv:2501.14627•Nature Communications•Jan 20, 2026•7 citations

High Fidelity Qubit Control in a Natural Si-MOS Quantum Dot using a 300 mm Silicon on Insulator Wafer

Xander Peetroons, Xunyao Luo, Tsung-Yeh Yang +26 more

We demonstrate high-fidelity single qubit control in a natural Si-MOS quantum dot fabricated in an industrial 300 mm wafer process on a silicon on insulator (SOI) wafer using electron spin resonance. A relatively high optimal Rabi frequency of 5 MHz is achieved, dynamically decoupling the electron spin from its 29-Si environment. Tracking the qubit frequency reduces the impact of low frequency noise in the qubit frequency and improves the $T^{Rabi}$ from 7 to 11 $μ$s at a Rabi frequency of 5 MHz, resulting in Q-factors exceeding 50. Randomized benchmarking returns an average single gate control fidelity of 99.5 $\pm$ 0.3%. As a result of pulse-area calibration, this fidelity is limited by the Rabi Q-factor. These results show that a fast Rabi frequency, low charge noise, and a feedback protocol enable high fidelity in these Si-MOS devices, despite the low-frequency magnetic noise.

cond-mat.mes-hallCross-listedarXiv:2512.05052•Applied Physics Letters•Dec 5, 2025•0 citations

High-fidelity singlet-triplet S−T− qubits in inhomogeneous magnetic fields

Clement H. Wong, M. A. Eriksson, S. N. Coppersmith +1 more

We propose an optimized set of quantum gates for a singlet-triplet qubit in a double quantum dot with two electrons utilizing the $S\text{\ensuremath{-}}{T}_{\ensuremath{-}}$ subspace. Qubit rotations are driven by the applied magnetic field and a field gradient provided by a micromagnet. We optimize the fidelity of this qubit as a function of the magnetic fields, taking advantage of ``sweet spots'' where the rotation frequencies are independent of the energy level detuning, providing protection against charge noise. We simulate gate operations and qubit rotations in the presence of quasistatic noise from charge and nuclear spins as well as leakage to nonqubit states. Our results show that, for silicon quantum dots, gate fidelities greater than $99%$ should be realizable, for rotations about two nearly orthogonal axes.

arXiv:1410.2310•Physical Review B•Jul 6, 2015•18 citations

A Degenerate Singlet-Triplet Qubit with All-Electrical Orthogonal Control

Phuong X. Nguyen, Konstantinos Tsoukalas, Jann H. Ungerer +8 more

Singlet-triplet qubits offer an attractive encoding for semiconductor quantum computing, combining ancilla-free readout, reduced sensitivity to common-mode noise, and baseband voltage control. However, the Zeeman energy difference $ΔE_\mathrm{Z}$ is typically fixed by local magnetic field gradients or $g$-factor inhomogeneities, leaving the exchange interaction $J$ as the only dynamically tunable parameter. This always-on $ΔE_\mathrm{Z}$ precludes orthogonal control of the qubit's rotation axes and introduces unwanted state rotations during idling. Here we demonstrate all-electrical orthogonal control of a degenerate singlet-triplet (DST) qubit formed by two hole spins in a germanium double quantum dot. Exploiting the electrically tunable anisotropic $g$-factors of the two spins, we identify a regime where both $ΔE_\mathrm{Z}$ and $J$ vanish, making the $S$ and $T_0$ states degenerate at the idle point. By applying only baseband voltage pulses, we independently control both $J$ and $ΔE_\mathrm{Z}$, enabling fully orthogonal $Z$- and $X$-axis rotations. Randomized benchmarking yields an average physical single-qubit gate fidelity of 99.53\% for a gate duration of approximately 100 ns. Finally, we electrically tune the degenerate point across a wide range of magnetic field orientations, enabling operation in a regime of enhanced coherence time and offering a route towards multi-qubit scaling under a shared global magnetic field.

cond-mat.mes-hallCross-listedarXiv:2607.27067•Jul 30, 2026•0 citations

High-fidelity resonant gating of a silicon-based quantum dot hybrid qubit

Dohun Kim, Daniel R Ward, C. B. Simmons +5 more

Abstract We implement resonant single qubit operations on a semiconductor hybrid qubit hosted in a three-electron Si/SiGe double quantum dot structure. By resonantly modulating the double dot energy detuning and employing electron tunnelling-based readout, we achieve fast (>100 MHz) Rabi oscillations and purely electrical manipulations of the three-electron spin states. We demonstrate universal single qubit gates using a Ramsey pulse sequence as well as microwave phase control, the latter of which shows control of an arbitrary rotation axis on the X–Y plane of the Bloch sphere. Quantum process tomography yields π rotation gate fidelities higher than 93 (96)% around the X (Z) axis of the Bloch sphere. We further show that the implementation of dynamic decoupling sequences on the hybrid qubit enables coherence times longer than 150 ns.

arXiv:1502.03156•npj Quantum Information•Oct 26, 2015•95 citations

Fast high-fidelity geometric gates for singlet-triplet qubits

Meiya Chen, Chengxian Zhang, Zheng‐Yuan Xue

Geometric gates that use the global property of the geometric phase is believed to be a powerful tool to realize fault-tolerant quantum computation. However, for singlet-triplet qubits in semiconductor quantum dot, the low Rabi frequency of the microwave control leads to overly long gating time, and thus the constructing geometric gate suffers more from the decoherence effect. Here we investigate the key issue of whether the fast geometric gate can be realized for singlet-triplet qubits without introducing an extra microwave-driven pulse, while maintaining the high-fidelity gate operation at the same time. We surprisingly find that both the single- and two-qubit geometric gates can be implemented via only modulating the time-dependent exchange interaction of the Hamiltonian, which can typically be on the order of $\ensuremath{\sim}\mathrm{GHz}$, and thus the corresponding gate time is of several nanoseconds. Furthermore, the obtained geometric gates are superior to their counterparts, i.e., the conventional dynamical gates for singlet-triplet qubits, with a relatively high fidelity surpassing 99%. Therefore our scheme is particularly applied to singlet-triplet qubits to obtain fast and high-fidelity geometric gates. Our scheme can also be extended to other systems without a microwave drive.

arXiv:2111.07705•Physical Review A•Feb 24, 2022•7 citations
We report a resonantly driven singlet–triplet (ST) qubit in a silicon metal–oxide–semiconductor (SiMOS) device operated without an applied external magnetic field. By resonantly modulating the exchange interaction at the qubit frequency, f q = 36 MHz , we observe coherent Rabi oscillations at f R = 1.69 MHz . A Ramsey measurement gives a dephasing time T 2 ∗ = 1.83 μ s , and randomized benchmarking yields an average single-qubit gate fidelity of 99.48%. These results demonstrate that the residual micromagnet field gradient is sufficient to support high-fidelity resonant control without a continuously applied external magnetic field.
Abstract In semiconductor hole spin qubits, low magnetic field ( B ) operation extends the coherence time ( T2∗{T}_{2}^{*}T2∗​ T 2 * ) but proportionally reduces the gate speed. In contrast, singlet-triplet (ST) qubits are primarily controlled by the exchange interaction ( J ) and can thus maintain high gate speeds even at low B . However, a large J introduces a significant charge component to the qubit, rendering ST qubits more vulnerable to charge noise when driven. Here, we demonstrate a highly coherent ST hole spin qubit in germanium, operating at both low B and low J . By modulating J , we achieve resonant driving of the ST qubit, obtaining an average gate fidelity of 99.68% and a coherence time of T2∗=1.9 μs{T}_{2}^{*}=1.9\,\mu {{{\rm{s}}}}T2∗​=1.9μs T 2 * = 1.9 μ s . Moreover, by applying the resonant drive continuously, we realize a dressed ST qubit with a tenfold increase in coherence time ( T2ρ∗=20.3 μs{T}_{2\rho }^{*}=20.3\,\mu {{{\rm{s}}}}T2ρ∗​=20.3μs T 2 ρ * = 20.3 μ s ). Frequency modulation of the driving signal enables universal control, with an average gate fidelity of 99.63%. Our results demonstrate the potential for extending coherence times while preserving high-fidelity control of germanium-based ST qubits, paving the way for more efficient operations in semiconductor-based quantum processors.
We demonstrate high-fidelity single qubit control in a natural Si-MOS quantum dot fabricated in an industrial 300 mm wafer process on a silicon on insulator (SOI) wafer using electron spin resonance. A relatively high optimal Rabi frequency of 5 MHz is achieved, dynamically decoupling the electron spin from its 29-Si environment. Tracking the qubit frequency reduces the impact of low frequency noise in the qubit frequency and improves the TRabiT^{Rabi}TRabi from 7 to 11 μμμs at a Rabi frequency of 5 MHz, resulting in Q-factors exceeding 50. Randomized benchmarking returns an average single gate control fidelity of 99.5 ±\pm± 0.3%. As a result of pulse-area calibration, this fidelity is limited by the Rabi Q-factor. These results show that a fast Rabi frequency, low charge noise, and a feedback protocol enable high fidelity in these Si-MOS devices, despite the low-frequency magnetic noise.
We propose an optimized set of quantum gates for a singlet-triplet qubit in a double quantum dot with two electrons utilizing the $S\text{\ensuremath{-}}{T}_{\ensuremath{-}}$ subspace. Qubit rotations are driven by the applied magnetic field and a field gradient provided by a micromagnet. We optimize the fidelity of this qubit as a function of the magnetic fields, taking advantage of ``sweet spots'' where the rotation frequencies are independent of the energy level detuning, providing protection against charge noise. We simulate gate operations and qubit rotations in the presence of quasistatic noise from charge and nuclear spins as well as leakage to nonqubit states. Our results show that, for silicon quantum dots, gate fidelities greater than 9999%99 should be realizable, for rotations about two nearly orthogonal axes.
Singlet-triplet qubits offer an attractive encoding for semiconductor quantum computing, combining ancilla-free readout, reduced sensitivity to common-mode noise, and baseband voltage control. However, the Zeeman energy difference ΔEZΔE_\mathrm{Z}ΔEZ​ is typically fixed by local magnetic field gradients or ggg-factor inhomogeneities, leaving the exchange interaction JJJ as the only dynamically tunable parameter. This always-on ΔEZΔE_\mathrm{Z}ΔEZ​ precludes orthogonal control of the qubit's rotation axes and introduces unwanted state rotations during idling. Here we demonstrate all-electrical orthogonal control of a degenerate singlet-triplet (DST) qubit formed by two hole spins in a germanium double quantum dot. Exploiting the electrically tunable anisotropic ggg-factors of the two spins, we identify a regime where both ΔEZΔE_\mathrm{Z}ΔEZ​ and JJJ vanish, making the SSS and T0T_0T0​ states degenerate at the idle point. By applying only baseband voltage pulses, we independently control both JJJ and ΔEZΔE_\mathrm{Z}ΔEZ​, enabling fully orthogonal ZZZ- and XXX-axis rotations. Randomized benchmarking yields an average physical single-qubit gate fidelity of 99.53\% for a gate duration of approximately 100 ns. Finally, we electrically tune the degenerate point across a wide range of magnetic field orientations, enabling operation in a regime of enhanced coherence time and offering a route towards multi-qubit scaling under a shared global magnetic field.
Abstract We implement resonant single qubit operations on a semiconductor hybrid qubit hosted in a three-electron Si/SiGe double quantum dot structure. By resonantly modulating the double dot energy detuning and employing electron tunnelling-based readout, we achieve fast (>100 MHz) Rabi oscillations and purely electrical manipulations of the three-electron spin states. We demonstrate universal single qubit gates using a Ramsey pulse sequence as well as microwave phase control, the latter of which shows control of an arbitrary rotation axis on the X–Y plane of the Bloch sphere. Quantum process tomography yields π rotation gate fidelities higher than 93 (96)% around the X (Z) axis of the Bloch sphere. We further show that the implementation of dynamic decoupling sequences on the hybrid qubit enables coherence times longer than 150 ns.
Geometric gates that use the global property of the geometric phase is believed to be a powerful tool to realize fault-tolerant quantum computation. However, for singlet-triplet qubits in semiconductor quantum dot, the low Rabi frequency of the microwave control leads to overly long gating time, and thus the constructing geometric gate suffers more from the decoherence effect. Here we investigate the key issue of whether the fast geometric gate can be realized for singlet-triplet qubits without introducing an extra microwave-driven pulse, while maintaining the high-fidelity gate operation at the same time. We surprisingly find that both the single- and two-qubit geometric gates can be implemented via only modulating the time-dependent exchange interaction of the Hamiltonian, which can typically be on the order of $\ensuremath{\sim}\mathrm{GHz}$, and thus the corresponding gate time is of several nanoseconds. Furthermore, the obtained geometric gates are superior to their counterparts, i.e., the conventional dynamical gates for singlet-triplet qubits, with a relatively high fidelity surpassing 99%. Therefore our scheme is particularly applied to singlet-triplet qubits to obtain fast and high-fidelity geometric gates. Our scheme can also be extended to other systems without a microwave drive.