CNOT gates for fluxonium qubits via selective darkening of transitions

TL;DR

This paper proposes a CNOT gate scheme for fluxonium qubits using selective darkening of transitions, achieving very low error rates by leveraging fluxonium's long coherence times and anharmonicity.

Contribution

It introduces a novel two-qubit gate method based on selective transition darkening, with detailed analysis and error estimation for fluxonium qubits.

Findings

Gate error below 10^{-4} achievable with realistic parameters

Long coherence times and anharmonicity of fluxonium are crucial for performance

Method effectively prevents excitation to higher states during operation

Abstract

We analyze the cross-resonance effect for fluxonium circuits and investigate a two-qubit gate scheme based on selective darkening of a transition. In this approach, two microwave pulses at the frequency of the target qubit are applied simultaneously with a proper ratio between their amplitudes to achieve a controlled-NOT operation. We study in detail coherent gate dynamics and calculate gate error. With nonunitary effects accounted for, we demonstrate that gate error below $10^{-4}$ is possible for realistic hardware parameters. This number is facilitated by long coherence times of computational transitions and strong anharmonicity of fluxoniums, which easily prevents excitation to higher excited states during the gate microwave drive.