Simultaneous sweet-spot locking of gradiometric fluxonium qubits

• URL: http://arxiv.org/abs/2505.08769v2
• Date: Thu, 07 Aug 2025 12:32:07 GMT
• Title: Simultaneous sweet-spot locking of gradiometric fluxonium qubits
• Authors: Denis Bénâtre, Mathieu Féchant, Nicolas Zapata, Nicolas Gosling, Patrick Paluch, Thomas Reisinger, Ioan M. Pop,
• Abstract summary: Crosstalk between neighboring flux lines is necessary to bias the qubits at the zero-field sweet spot.<n>A solution is to use gradiometric loops, which incorporate a flux locking mechanism that, once a fluxon is trapped during symmetric, holds the device at the sweet spot.<n>We demonstrate this technique by simultaneously locking multiple gradiometric fluxonium qubits in which an aluminum loop retains the trapped fluxon indefinitely.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Efforts to scale up superconducting processors that employ flux-qubits face numerous challenges, among which is the crosstalk created by neighboring flux lines, which are necessary to bias the qubits at the zero-field and $\Phi_0/2$ sweet spots. A solution to this problem is to use symmetric gradiometric loops, which incorporate a flux locking mechanism that, once a fluxon is trapped during cooldown, holds the device at the sweet spot and limits the need for active biasing. We demonstrate this technique by simultaneously locking multiple gradiometric fluxonium qubits in which an aluminum loop retains the trapped fluxon indefinitely. By compensating the inductive asymmetry between the two loops of the design, we are able to lock the effective flux-bias within $\Phi_{eff} = -3 \times 10^{-4} \Phi_0$ from the target, corresponding to only 15 % degradation in $T_{2,E}$ when operated in zero external field. The design strategy demonstrated here reduces integration complexity for flux qubits by minimizing cross-talk and potentially eliminating the need for local flux bias.

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