Cross-resonance control of an oscillator with an auxiliary fluxonium qubit

TL;DR

This paper introduces a cross-resonance control scheme for an oscillator using a fluxonium qubit, achieving high-fidelity gates with minimal hardware overhead and robustness against certain errors, advancing quantum information processing capabilities.

Contribution

It proposes a fluxonium-based cross-resonance gate scheme with optimized parameters, demonstrating high fidelity and fast operation, improving fault tolerance and hardware efficiency.

Findings

Achieved unitary fidelity >99.9% for the gate

Demonstrated gate times of hundreds of nanoseconds

Provided a method to optimize device and gate parameters

Abstract

The conditional displacement (CD) gate between an oscillator and a discrete-variable auxiliary qubit plays a key role in quantum information processing tasks, such as enabling universal control of the oscillator and longitudinal readout of the qubit. However, the gate is unprotected against the propagation of auxiliary qubit decay errors and hence not fault-tolerant. Here, we propose a CD gate scheme with fluxonium as the auxiliary qubit, which has been experimentally demonstrated to have a large noise bias and millisecond-level lifetimes. The proposed gate is applied cross-resonantly by modulating the external flux of the fluxonium at the frequency of the target oscillator, which requires minimal hardware overhead and does not increase sensitivity to decoherence mechanisms like dephasing. We further provide a perturbative description of the gate mechanism and identify the error budget. Additionally, we develop an approximate procedure for choosing device and gate parameters that optimizes gate performance. Following the procedure for multiple sets of fluxonium parameters from the literature, we numerically demonstrate CD gates with unitary fidelity exceeding 99.9% and gate times of hundreds of nanoseconds.