Probing Residual Noise at a Decoherence Sweet Spot in a 28Si/SiGe Spin Qubit
Abstract
In 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 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* reaches 67 μs and the Carr-Purcell-Meiboom-Gill coherence time reaches 4.6 ms, whereas T2* is 5.2 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 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 29Si nuclear spin fluctuations.
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BibTeX
@misc{lee2026probing,
title = {{Probing Residual Noise at a Decoherence Sweet Spot in a $^28$Si/SiGe Spin Qubit}},
author = {Shinwoo Lee and Hanseo Sohn and Jaemin Park and Hyeongyu Jang and Jonginn Yun and Jun Yoneda and Lucas E. A. Stehouwer and Davide Degli Esposti and Giordano Scappucci and Dohun Kim},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.15860},
eprint = {2609.15860},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.15860},
}
RIS
TY - UNPB
TI - Probing Residual Noise at a Decoherence Sweet Spot in a ^28Si/SiGe Spin Qubit
AU - Shinwoo Lee
AU - Hanseo Sohn
AU - Jaemin Park
AU - Hyeongyu Jang
AU - Jonginn Yun
AU - Jun Yoneda
AU - Lucas E. A. Stehouwer
AU - Davide Degli Esposti
AU - Giordano Scappucci
AU - Dohun Kim
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.15860
UR - https://arxiv.org/abs/2609.15860
AB - In ^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 ^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, T_2^* reaches 67 μs and the Carr-Purcell-Meiboom-Gill coherence time reaches 4.6 ms, whereas T_2^* is 5.2 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 ^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 ^29Si nuclear spin fluctuations.
ER -