Fast high-fidelity gates for galvanically-coupled fluxonium qubits using strong flux modulation

TL;DR

This paper proposes a method for implementing high-fidelity entangling gates in fluxonium qubits using strong flux modulation, achieving fidelities above 99.9% in realistic conditions.

Contribution

It introduces a galvanic-coupling scheme with flux-tunable XX interaction and strong ac flux drives to realize fast, high-fidelity entangling gates beyond the rotating-wave approximation.

Findings

Predicted fidelity of >0.999 for the SWAP gate.

Gate durations are only a few drive periods.

Theoretical framework captures dynamics beyond RWA.

Abstract

Long coherence times, large anharmonicity and robust charge-noise insensitivity render fluxonium qubits an interesting alternative to transmons. Recent experiments have demonstrated record coherence times for low-frequency fluxonia. Here, we propose a galvanic-coupling scheme with flux-tunable $\textit{XX}$ coupling. To implement a high-fidelity entangling $\sqrt{i\mathrm{SWAP}}$ gate, we modulate the strength of this coupling and devise variable-time identity gates to synchronize required single-qubit operations. Both types of gates are implemented using strong ac flux drives, lasting for only a few drive periods. We employ a theoretical framework capable of capturing qubit dynamics beyond the rotating-wave approximation (RWA) as required for such strong drives. We predict an open-system fidelity of $F>0.999$ for the $\sqrt{i\mathrm{SWAP}}$ gate under realistic conditions.