Flux-noise-resilient transmon qubit via a doubly-connected gradiometric design
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arXiv
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| Autori principali: | , , , , , , , , , , , , , , |
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| Natura: | Preprint |
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2026
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| author | Fu, J. B. Wang, Da-Wei Ren, B. Yang, Z. H. Hu, S. Huang, G. Y. Cao, S. H. Liu, D. D. Zhang, X. F. Fu, X. Xue, S. C. Che, Y. G. Liu, Yu-xi Deng, M. T. Wu, J. J. |
| author_facet | Fu, J. B. Wang, Da-Wei Ren, B. Yang, Z. H. Hu, S. Huang, G. Y. Cao, S. H. Liu, D. D. Zhang, X. F. Fu, X. Xue, S. C. Che, Y. G. Liu, Yu-xi Deng, M. T. Wu, J. J. |
| contents | Frequency-tunable superconducting transmon qubits are a cornerstone of scalable quantum processors, yet their performance is often degraded by sensitivity to low-frequency flux noise. Here we present a doubly-connected gradiometric transmon (the ``8-mon") that incorporates a nano-airbridge to link its two loops. This design preserves full electrical tunability and remains fully compatible with standard X-mon control and readout, requiring no additional measurement overhead. The airbridge interconnect eliminates dielectric loss, which enables the 8-mon to achieve both energy relaxation times $T_{\rm 1}$ comparable to reference X-mons and, in the small flux-bias regime, a nearly threefold enhancement in Ramsey coherence time $T_{\rm 2}^*$. This improved $T_{\rm 2}^*$ reaches the same order as $T_{\rm 1}$ without employing echo decoupling. The device also exhibits superior long-term frequency stability even without any magnetic field shielding. We develop a spatially correlated flux-noise model whose simulations quantitatively reproduce the experimental coherence trends, revealing the coexistence of short- and long-correlation-length magnetic noise in the superconducting chip environment. By unifying high tunability with intrinsic flux-noise suppression through a robust geometric design, the 8-mon provides a practical pathway toward more coherent and stable superconducting quantum processors. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_02137 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Flux-noise-resilient transmon qubit via a doubly-connected gradiometric design Fu, J. B. Wang, Da-Wei Ren, B. Yang, Z. H. Hu, S. Huang, G. Y. Cao, S. H. Liu, D. D. Zhang, X. F. Fu, X. Xue, S. C. Che, Y. G. Liu, Yu-xi Deng, M. T. Wu, J. J. Quantum Physics Frequency-tunable superconducting transmon qubits are a cornerstone of scalable quantum processors, yet their performance is often degraded by sensitivity to low-frequency flux noise. Here we present a doubly-connected gradiometric transmon (the ``8-mon") that incorporates a nano-airbridge to link its two loops. This design preserves full electrical tunability and remains fully compatible with standard X-mon control and readout, requiring no additional measurement overhead. The airbridge interconnect eliminates dielectric loss, which enables the 8-mon to achieve both energy relaxation times $T_{\rm 1}$ comparable to reference X-mons and, in the small flux-bias regime, a nearly threefold enhancement in Ramsey coherence time $T_{\rm 2}^*$. This improved $T_{\rm 2}^*$ reaches the same order as $T_{\rm 1}$ without employing echo decoupling. The device also exhibits superior long-term frequency stability even without any magnetic field shielding. We develop a spatially correlated flux-noise model whose simulations quantitatively reproduce the experimental coherence trends, revealing the coexistence of short- and long-correlation-length magnetic noise in the superconducting chip environment. By unifying high tunability with intrinsic flux-noise suppression through a robust geometric design, the 8-mon provides a practical pathway toward more coherent and stable superconducting quantum processors. |
| title | Flux-noise-resilient transmon qubit via a doubly-connected gradiometric design |
| topic | Quantum Physics |
| url | https://arxiv.org/abs/2601.02137 |