Flux-Trapping Fluxonium Qubit

In pursuit of realizing superconducting quantum computers, a fluxonium qubit has recently garnered attention [1]. A fluxonium qubit exhibits significant nonlinearity at the π- phase bias point, enabling fast and high-fidelity gate operations. Moreover, a coherence time exceeding 1 ms has been demonstrated [2], making fluxonium qubits an attractive candidate for the physical realization of a superconducting quantum processor. However, a major obstacle to the large-scale integration of fluxoniums is the need for precise external flux for the phase biasing. Introducing flux bias lines for each fluxonium is necessary to achieve high performance at its optimal bias point, while it tends to result in complex wiring overhead, undesirable crosstalk, and additional decoherence. Here, we propose a “flux-trapping fluxonium qubit,” which achieves the optimal phase bias without external flux bias at the operation temperature by leveraging the fluxoid quantization in a flux-trapping loop of a concentric fluxonium. We introduce the device structure and report on the phase biasing with an error of less than 0.1%.

[1] L. B. Nguyen et al., PRX Quantum 3, 037001 (2022).

[2] A. Somoroff et al., Phys. Rev. Lett. 130, 267001 (2023).