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This study demonstrates that operating silicon spin qubits at a decoherence sweet spot effectively suppresses charge noise transduction, isolating residual frequency noise to the fundamental limit imposed by $^{29}$Si nuclear spins. Achieving 4.6 ms coherence times in this configuration provides critical validation for scaling solid-state quantum processors where local noise management is paramount.
Probing Residual Noise at a Decoherence Sweet Spot in a $^{28}$Si/SiGe Spin Qubit
arXiv:2609.15860v1 Announce Type: new Abstract: In $^{28}$Si/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 $^{29}$Si, 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, $T_2^*$ reaches 67 $\mu\mathrm{s}$ and the Carr-Purcell-Meiboom-Gill coherence time reaches 4.6 ms, whereas $T_2^*$ is 5.2 $\mu\mathrm{s}$ 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 $^{29}$Si 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 $^{29}$Si nuclear spin fluctuations.
Authors:Shinwoo Lee (1), Hanseo Sohn (1), Jaemin Park (1), Hyeongyu Jang (1), Jonginn Yun (1), Jun Yoneda (2), Lucas E. A. Stehouwer (3), Davide Degli Esposti (3), Giordano Scappucci (3), Dohun Kim (1) ((1) Seoul National University, (2) The University of Tokyo, (3) Delft University of Technology)
Abstract:In $^{28}$Si/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 $^{29}$Si, 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, $T_2^*$ reaches 67 $\mu\mathrm{s}$ and the Carr-Purcell-Meiboom-Gill coherence time reaches 4.6 ms, whereas $T_2^*$ is 5.2 $\mu\mathrm{s}$ 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 $^{29}$Si 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 $^{29}$Si nuclear spin fluctuations.
11 pages, 6 figures + 6 pages Supplemental Material, 3 figures. Shinwoo Lee and Hanseo Sohn contributed equally
Quantum Physics (quant-ph); Applied Physics (physics.app-ph)
arXiv:2609.15860 [quant-ph]
(or arXiv:2609.15860v1 [quant-ph] for this version)
https://doi.org/10.48550/arXiv.2609.15860 arXiv-issued DOI via DataCite (pending registration)
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