Tunable coupling scheme for implementing two-qubit gates on fluxonium qubits

TL;DR

This paper introduces a tunable coupling scheme for fixed-frequency fluxonium qubits, enabling high-precision two-qubit gates within a planar on-chip architecture, compatible with existing hardware and leveraging fluxonium's advantageous properties.

Contribution

The paper proposes a novel tunable coupling method for fluxonium qubits, demonstrating its effectiveness through simulation of a universal two-qubit fSim gate.

Findings

Simulated high-fidelity two-qubit gates using the proposed scheme

Compatible with existing transmon hardware architectures

Lower qubit frequency enables more precise control

Abstract

The superconducting fluxonium circuit is an RF-SQUID-type flux qubit that uses a large inductance built from an array of Josephson junctions or a high kinetic inductance material. This inductance suppresses charge sensitivity exponentially and flux sensitivity quadratically. In contrast to the transmon qubit, the anharmonicity of fluxonium can be large and positive, allowing for better separation between the low energy qubit manifold of the circuit and higher-lying excited states. Here, we propose a tunable coupling scheme for implementing two-qubit gates on fixed-frequency fluxonium qubits, biased at half flux quantum. In this system, both qubits and coupler are coupled capacitively and implemented as fluxonium circuits with an additional harmonic mode. We investigate the performance of the scheme by simulating a universal two-qubit fSim gate. In the proposed approach, we rely on a planar on-chip architecture for the whole device. Our design is compatible with existing hardware for transmon-based devices, with the additional advantage of lower qubit frequency facilitating high-precision gating.