Simultaneous sweet-spot locking of gradiometric fluxonium qubits

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.

10 pages, 12 figures

References in corpus (10)

• Fluxonium: an alternative qubit platform for high-fidelity operations
• High-Fidelity, Frequency-Flexible Two-Qubit Fluxonium Gates with a Transmon Coupler
• High fidelity two-qubit gates on fluxoniums using a tunable coupler
• Scalable High-Performance Fluxonium Quantum Processor
• Scqubits: a Python package for superconducting qubits
• Gradiometric flux qubits with tunable gap
• Operating in a deep underground facility improves the locking of gradiometric fluxonium qubits at the sweet spots
• Superconducting flux qubit with ferromagnetic Josephson $\pi$-junction operating at zero magnetic field
• Learning-based Calibration of Flux Crosstalk in Transmon Qubit Arrays
• Magnetic penetration depth of Aluminum thin films