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arXiv:2610.41890

Control-Noise Trade-offs in Industrially Integrated ${}^{28}\mathrm{Si}/\mathrm{SiGe}$ Spin-1/2 Qubits

Leon C. Camenzind, Ik Kyeong Jin, Yi-Hsien Wu, Akito Noiri, Kenta Takeda, Takashi Nakajima, Takashi Kobayashi, Giordano Scappucci, Seigo Tarucha

quant-phcond-mat.mes-hallSubmitted Oct 30, 2026• Announced Nov 2, 2026
arXivHTMLPDF

Abstract

Scaling silicon spin qubits to fault-tolerant processors requires semiconductor foundry integration, yet it remains unclear how industrial fabrication and dense device integration affect qubit control and noise. Here we study ${}^{28}\mathrm{Si}/\mathrm{SiGe}$ electron spin-1/2 qubits fabricated using Intel's industry-compatible 300 mm process and incorporating micromagnets for electrically driven spin resonance, using a high-performance device fabricated in the RIKEN research cleanroom as a reference. Primitive $π/2$-gate fidelities reach the 99.99% level in the Intel devices, which also exhibit longer idle coherence, weaker low-frequency correlations and reduced qubit-to-qubit variability across several measured characteristics. In the present Intel devices, the micromagnets are integrated inline with the back-end-of-line (BEOL) contact routing, with their separation from the quantum well set through the vertical stack design. Relative to the reference, their larger separation contributes to weaker longitudinal and transverse magnetic-field gradients. The weaker longitudinal gradient suppresses the conversion of charge noise into qubit-frequency fluctuations, whereas the weaker transverse gradient reduces electrically driven spin-resonance efficiency and makes drive-dependent errors relevant at lower Rabi frequencies. Additional BEOL routing and metal levels required for two-dimensional arrays make such placement decisions increasingly consequential when scaling. These results establish an integration-level control-noise trade-off linking micromagnet placement within densely routed layouts to achievable gate performance, while very high-fidelity operation remains possible in industrially fabricated devices.

AI Summary

The paper examines how micromagnet placement within industrial interconnect stacks affects the balance between electrical spin control and noise sensitivity in $^{28}\mathrm{Si}/\mathrm{SiGe}$ qubits. It compares two three-qubit devices fabricated using Intel’s industry-compatible 300 mm process with a five-qubit academic reference, using coherence measurements, frequency-noise spectroscopy, inter-qubit cross-spectra, randomized benchmarking (RB), and microwave-power-dependent measurements. The industrial devices have larger micromagnet–quantum-well separation and weaker simulated transverse gradients: $0.4$–$0.5\,\mathrm{mT/nm}$ versus approximately $1.15\,\mathrm{mT/nm}$. Reaching a 1 MHz Rabi frequency requires 7.7 dB higher median nominal microwave power. Weaker longitudinal gradients reduce charge-to-frequency-noise conversion: median Hahn-echo coherence is approximately $200\,\mu\mathrm{s}$ versus $70\,\mu\mathrm{s}$, and CPMG coherence at 1024 pulses is $3.88\pm0.09$ ms versus $1.49\pm0.31$ ms. Sensor-referred charge noise is comparable, indicating reduced susceptibility rather than a quieter charge environment. Weaker low-frequency inter-qubit correlations and occupation-dependent dephasing are interpreted as evidence for predominantly uncorrelated residual nuclear-spin noise. RB-derived primitive $\pi/2$ fidelities reach approximately 99.99% in industrial devices and 99.999% in the reference. Industrial-device errors rise at lower Rabi frequencies; spin-lock and off-resonant CPMG measurements support microwave-induced noise as a limitation beyond measured detuning shifts. The comparison involves few devices with differing geometries, heterostructures, operating points, and cryogenic setups; microwave powers are not calibrated in situ. Nuclear-noise attribution remains interpretive, and irradiation-duration differences prevent separating frequency-dependent noise from time-dependent heating or fluctuator activation. The proposed scaling constraint concerns micromagnet placement, not industrial fabrication intrinsically.

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28 pages, 4 main figures and 5 extended data figures

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Control-Noise Trade-offs in Industrially Integrated 28Si/SiGe{}^{28}\mathrm{Si}/\mathrm{SiGe}28Si/SiGe Spin-1/2 Qubits
Scaling silicon spin qubits to fault-tolerant processors requires semiconductor foundry integration, yet it remains unclear how industrial fabrication and dense device integration affect qubit control and noise. Here we study 28Si/SiGe{}^{28}\mathrm{Si}/\mathrm{SiGe}28Si/SiGe electron spin-1/2 qubits fabricated using Intel's industry-compatible 300 mm process and incorporating micromagnets for electrically driven spin resonance, using a high-performance device fabricated in the RIKEN research cleanroom as a reference. Primitive π/2π/2π/2-gate fidelities reach the 99.99% level in the Intel devices, which also exhibit longer idle coherence, weaker low-frequency correlations and reduced qubit-to-qubit variability across several measured characteristics. In the present Intel devices, the micromagnets are integrated inline with the back-end-of-line (BEOL) contact routing, with their separation from the quantum well set through the vertical stack design. Relative to the reference, their larger separation contributes to weaker longitudinal and transverse magnetic-field gradients. The weaker longitudinal gradient suppresses the conversion of charge noise into qubit-frequency fluctuations, whereas the weaker transverse gradient reduces electrically driven spin-resonance efficiency and makes drive-dependent errors relevant at lower Rabi frequencies. Additional BEOL routing and metal levels required for two-dimensional arrays make such placement decisions increasingly consequential when scaling. These results establish an integration-level control-noise trade-off linking micromagnet placement within densely routed layouts to achievable gate performance, while very high-fidelity operation remains possible in industrially fabricated devices.
The paper examines how micromagnet placement within industrial interconnect stacks affects the balance between electrical spin control and noise sensitivity in 28Si/SiGe^{28}\mathrm{Si}/\mathrm{SiGe}28Si/SiGe qubits. It compares two three-qubit devices fabricated using Intel’s industry-compatible 300 mm process with a five-qubit academic reference, using coherence measurements, frequency-noise spectroscopy, inter-qubit cross-spectra, randomized benchmarking (RB), and microwave-power-dependent measurements.
The industrial devices have larger micromagnet–quantum-well separation and weaker simulated transverse gradients: 0.40.40.4–0.5 mT/nm0.5\,\mathrm{mT/nm}0.5mT/nm versus approximately 1.15 mT/nm1.15\,\mathrm{mT/nm}1.15mT/nm. Reaching a 1 MHz Rabi frequency requires 7.7 dB higher median nominal microwave power. Weaker longitudinal gradients reduce charge-to-frequency-noise conversion: median Hahn-echo coherence is approximately 200 μs200\,\mu\mathrm{s}200μs versus 70 μs70\,\mu\mathrm{s}70μs, and CPMG coherence at 1024 pulses is 3.88±0.093.88\pm0.093.88±0.09 ms versus 1.49±0.311.49\pm0.311.49±0.31 ms. Sensor-referred charge noise is comparable, indicating reduced susceptibility rather than a quieter charge environment. Weaker low-frequency inter-qubit correlations and occupation-dependent dephasing are interpreted as evidence for predominantly uncorrelated residual nuclear-spin noise.
RB-derived primitive π/2\pi/2π/2 fidelities reach approximately 99.99% in industrial devices and 99.999% in the reference. Industrial-device errors rise at lower Rabi frequencies; spin-lock and off-resonant CPMG measurements support microwave-induced noise as a limitation beyond measured detuning shifts.
The comparison involves few devices with differing geometries, heterostructures, operating points, and cryogenic setups; microwave powers are not calibrated in situ. Nuclear-noise attribution remains interpretive, and irradiation-duration differences prevent separating frequency-dependent noise from time-dependent heating or fluctuator activation. The proposed scaling constraint concerns micromagnet placement, not industrial fabrication intrinsically.
Practical quantum computers require a large network of highly coherent qubits, interconnected in a design robust against errors. Donor spins in silicon provide state-of-the-art coherence and quantum gate fidelities, in a platform adapted from industrial semiconductor processing. Here we present a scalable design for a silicon quantum processor that does not require precise donor placement and leaves ample space for the routing of interconnects and readout devices. We introduce the flip-flop qubit, a combination of the electron-nuclear spin states of a phosphorus donor that can be controlled by microwave electric fields. Two-qubit gates exploit a second-order electric dipole-dipole interaction, allowing selective coupling beyond the nearest-neighbor, at separations of hundreds of nanometers, while microwave resonators can extend the entanglement to macroscopic distances. We predict gate fidelities within fault-tolerance thresholds using realistic noise models. This design provides a realizable blueprint for scalable spin-based quantum computers in silicon.Quantum computers will require a large network of coherent qubits, connected in a noise-resilient way. Tosi et al. present a design for a quantum processor based on electron-nuclear spins in silicon, with electrical control and coupling schemes that simplify qubit fabrication and operation.
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.
Abstract Among the many types of qubit presently being investigated for a future quantum computer, silicon spin qubits with millions of qubits on a single chip are uniquely positioned to enable quantum computing. However, it has not been clear whether the outstanding high-fidelity operations and long coherence times shown by silicon spin qubits fabricated in academic settings 1–8 can be reliably reproduced when the qubits are manufactured in a semiconductor foundry 9–11 . Here we show precise qubit operation of silicon two-qubit devices made with standard semiconductor tooling in a 300-mm foundry environment. Of the key metrics, single- and two-qubit control fidelities exceed 99% for all four devices, and the state preparation and measurement fidelities reach up to 99.9%, as evidenced by gate set tomography. We report spin lifetime and coherence up to T 1 = 9.5 s, T2∗=40.6 μs{T}_{2}^{* }=40.6\,{\rm{\mu }}{\rm{s}}T2∗​=40.6μs T 2 * = 40.6 μ s and T2Hahn=1.9 ms{T}_{2}^{{\rm{Hahn}}}=1.9\,{\rm{ms}}T2Hahn​=1.9ms T 2 Hahn = 1.9 ms . We determine that residual nuclear spin-carrying isotopes contribute substantially to operational errors, identifying further isotopic purification as a clear pathway to even higher performance.
The path to fault-tolerant quantum computing hinges on hardware that scales while remaining compatible with quantum error correction (QEC). Silicon spin qubits are a leading hardware candidate because they combine industrial fabrication compatibility with a nanoscale footprint that could accommodate millions of qubits on a chip. However, their suitability for QEC remains uncertain since spatially correlated noise naturally emerges from the resulting close proximity of qubits. These correlations increase the likelihood of simultaneous errors and erode the redundancy that QEC depends on. Here we quantify the spatial extent of noise correlations in a five-qubit silicon array and assess their impact on QEC. We identify two distinct sources of correlated noise: global magnetic field drifts that generate perfectly correlated fluctuations, and charge noise from two-level fluctuators that produces short-range correlations decaying within neighboring qubits. While magnetic drifts represent a critical correlated noise source that can compromise QEC, they can be mitigated. In contrast, the measured charge noise correlations are moderate, electrically tunable, and compatible with fault-tolerant operation with minimal qubit overhead. Our results establish quantitative benchmarks for correlated noise and clarify how such correlations impact the viability of quantum error correction in scalable qubit arrays.
Probing Residual Noise at a Decoherence Sweet Spot in a 28^{28}28Si/SiGe Spin Qubit
In 28^{28}28Si/SiGe spin qubits with micromagnets, the longitudinal stray field gradient transduces charge noise into qubit frequency noise and limits coherence. We compare two neighboring qubits in the same device with 800 ppm residual 29^{29}29Si, one near a decoherence sweet spot where the gradient is locally minimized and the other at a position with a larger gradient. At the sweet spot, T2∗T_2^*T2∗​ reaches 67 μsμ\mathrm{s}μs and the Carr-Purcell-Meiboom-Gill coherence time reaches 4.6 ms, whereas T2∗T_2^*T2∗​ is 5.2 μsμ\mathrm{s}μs at the neighboring qubit. Near 1 Hz, the frequency noise power spectral density at the sweet spot is nearly two orders of magnitude lower than at the neighboring qubit. The magnitude and low-frequency decay of the residual spectrum are compatible with the prediction for 29^{29}29Si nuclear spin noise, and the weak interqubit correlation indicates that local noise becomes important for dephasing at the sweet spot. Despite a finite correlation with the charge sensor, sweet-spot operation strongly reduced the transduction of charge noise, bringing the residual frequency noise close to the level predicted for 29^{29}29Si nuclear spin fluctuations.
The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise.During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit.However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood.We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by highfrequency charge noise rather than the quasistatic noise inherent to any semiconductor device.We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04 Æ 0.23% in a gallium arsenide quantum dot.We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1=f noise observed in isotopically purified silicon qubits.