Flux-noise-resilient transmon qubit via a doubly-connected gradiometric design

• URL: http://arxiv.org/abs/2601.02137v1
• Date: Mon, 05 Jan 2026 14:07:40 GMT
• Title: Flux-noise-resilient transmon qubit via a doubly-connected gradiometric design
• Authors: J. B. Fu, Da-Wei Wang, B. Ren, Z. H. Yang, S. Hu, G. Y. Huang, S. H. Cao, D. D. Liu, X. F. Zhang, X. Fu, S. C. Xue, Y. G. Che, Yu-xi Liu, M. T. Deng, J. J. Wu,
• Abstract summary: We present a doubly-connected gradiometric transmon that incorporates a nano-airbridge to link its two loops.<n>The design preserves full electrical tunability and remains fully compatible with standard X-mon control and readout.<n>The device also exhibits superior long-term frequency stability even without any magnetic field shielding.
• Score: 3.9569312312512213
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: 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.

Related papers

• Frequency-Multiplexed Millimeter-Wave Fault-Tolerant Superconducting Qubits Enabled by an On-Chip Nonreciprocal Control Bus [0.0]
  Scaling superconducting quantum processors is fundamentally limited by the escalating effects of microwave crosstalk and decay Purcell.<n>This paper proposes the concept of frequency-multiplexed millimeter-wave superconducting qubits.<n>It demonstrates a novel architecture that integrates an on-chip cryogenic nonreciprocal space-time-periodic superconducting frequency multiplier.
  arXiv  Detail & Related papers  (2025-12-19T13:57:17Z)
• Tunable Superconducting Quantum Interference Device Coupler for Fluxonium Qubits [0.8691965235932587]
  Tunable couplers enable high-fidelity two-qubit gates leveraging high on/off coupling ratios and reduced crosstalk within a single design.<n>We present two schemes to implement two-qubit gates, predicting a $sqrtitextSWAP$-like gate with $99.9%$ open-system fidelity in less than 6 nanoseconds.
  arXiv  Detail & Related papers  (2025-08-23T05:42:59Z)
• Parameter optimization for the unimon qubit [0.0]
  Inductively shunted superconducting qubits, such as the unimon qubit, combine high anharmonicity with protection from low-frequency charge noise.<n>We develop accurate closed-form approximations for the frequency and anharmonicity of the unimon qubit.<n>We show that the proposed qubit parameters have potential to enhance the single-qubit gate fidelity of the unimon beyond $99.99%$.
  arXiv  Detail & Related papers  (2025-04-28T19:13:59Z)
• Erasure qubits: Overcoming the $T_1$ limit in superconducting circuits [105.54048699217668]
  amplitude damping time, $T_phi$, has long stood as the major factor limiting quantum fidelity in superconducting circuits. We propose a scheme for overcoming the conventional $T_phi$ limit on fidelity by designing qubits in a way that amplitude damping errors can be detected and converted into erasure errors.
  arXiv  Detail & Related papers  (2022-08-10T17:39:21Z)
• Enhancing the Coherence of Superconducting Quantum Bits with Electric Fields [62.997667081978825]
  We show that qubit coherence can be improved by tuning defects away from the qubit resonance using an applied DC-electric field. We also discuss how local gate electrodes can be implemented in superconducting quantum processors to enable simultaneous in-situ coherence optimization of individual qubits.
  arXiv  Detail & Related papers  (2022-08-02T16:18:30Z)
• Topological Josephson parametric amplifier array: A proposal for directional, broadband, and low-noise amplification [39.58317527488534]
  Low-noise microwave amplifiers are crucial for detecting weak signals in fields such as quantum technology and radio astronomy. We show that compact devices with few sites can achieve exceptional performance, with gains exceeding 20 dB over a bandwidth ranging from hundreds of MHz to GHz. The device also operates near the quantum noise limit and provides topological protection against up to 15% fabrication disorder.
  arXiv  Detail & Related papers  (2022-07-27T18:07:20Z)
• Demonstration of the Two-Fluxonium Cross-Resonance Gate [1.8568045743509223]
  Current implementations of two-qubit gates compromise fluxonium's coherence properties. We realize a fast all-microwave cross-resonance gate between two capacitively-coupled fluxoniums. Our results project a possible pathway towards reducing the two-qubit error rate below $10-4$ with present-day technologies.
  arXiv  Detail & Related papers  (2022-04-25T17:59:17Z)
• A fast tunable 3D-transmon architecture for superconducting qubit-based hybrid devices [0.0]
  We introduce a fast-flux line for a frequency tunable transmon qubit in 3D cavity architecture. We investigate the flux-dependent dynamic range, relaxation from unconfined states, and the bandwidth of the flux-line.
  arXiv  Detail & Related papers  (2022-04-01T06:59:11Z)
• High fidelity two-qubit gates on fluxoniums using a tunable coupler [47.187609203210705]
  Superconducting fluxonium qubits provide a promising alternative to transmons on the path toward large-scale quantum computing. A major challenge for multi-qubit fluxonium devices is the experimental demonstration of a scalable crosstalk-free multi-qubit architecture. Here, we present a two-qubit fluxonium-based quantum processor with a tunable coupler element.
  arXiv  Detail & Related papers  (2022-03-30T13:44:52Z)
• Unimon qubit [42.83899285555746]
  Superconducting qubits are one of the most promising candidates to implement quantum computers. Here, we introduce and demonstrate a superconducting-qubit type, the unimon, which combines the desired properties of high non-linearity, full insensitivity to dc charge noise, insensitivity to flux noise, and a simple structure consisting only of a single Josephson junction in a resonator.
  arXiv  Detail & Related papers  (2022-03-11T12:57:43Z)
• Superconducting coupler with exponentially large on-off ratio [68.8204255655161]
  Tunable two-qubit couplers offer an avenue to mitigate errors in multiqubit superconducting quantum processors. Most couplers operate in a narrow frequency band and target specific couplings, such as the spurious $ZZ$ interaction. We introduce a superconducting coupler that alleviates these limitations by suppressing all two-qubit interactions with an exponentially large on-off ratio.
  arXiv  Detail & Related papers  (2021-07-21T03:03:13Z)
• Fast high-fidelity single-qubit gates for flip-flop qubits in silicon [68.8204255655161]
  flip-flop qubit is encoded in the states with antiparallel donor-bound electron and donor nuclear spins in silicon. We study the multilevel system that is formed by the interacting electron and nuclear spins. We propose an optimal control scheme that produces fast and robust single-qubit gates in the presence of low-frequency noise.
  arXiv  Detail & Related papers  (2021-01-27T18:37:30Z)
• Optimal coupling of HoW$_{10}$ molecular magnets to superconducting circuits near spin clock transitions [85.83811987257297]
  We study the coupling of pure and magnetically diluted crystals of HoW$_10$ magnetic clusters to microwave superconducting coplanar waveguides. Results show that engineering spin-clock states of molecular systems offers a promising strategy to combine sizeable spin-photon interactions with a sufficient isolation from unwanted magnetic noise sources.
  arXiv  Detail & Related papers  (2019-11-18T11:03:06Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.