Native Approach to Controlled-<math display="inline"><mrow><mi>Z</mi></mrow></math> Gates in Inductively Coupled Fluxonium Qubits

Ma, Xizheng; Zhang, Gengyan; Wu, Feng; Bao, Feng; Chang, Xu; Chen, Jianjun; Deng, Hao; Gao, Ran; Gao, Xun; Hu, Lijuan

doi:10.1103/PhysRevLett.132.060602

Native Approach to Controlled- $Z$ Gates in Inductively Coupled Fluxonium Qubits

Aug 30, 2023

19 pages

Published in:

Phys.Rev.Lett. 132 (2024) 6, 060602

Published: Feb 8, 2024

e-Print:

2308.16040 [quant-ph]

DOI:

10.1103/PhysRevLett.132.060602 (publication)

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Abstract: (APS)

The fluxonium qubits have emerged as a promising platform for gate-based quantum information processing. However, their extraordinary protection against charge fluctuations comes at a cost: when coupled capacitively, the qubit-qubit interactions are restricted to

X X

interactions. Consequently, effective

Z Z

or

X Z

interactions are only constructed either by temporarily populating higher-energy states, or by exploiting perturbative effects under microwave driving. Instead, we propose and demonstrate an inductive coupling scheme, which offers a wide selection of native qubit-qubit interactions for fluxonium. In particular, we leverage a built-in, flux-controlled

Z Z

interaction to perform qubit entanglement. To combat the increased flux-noise-induced dephasing away from the flux-insensitive position, we use a continuous version of the dynamical decoupling scheme to perform noise filtering. Combining these, we demonstrate a 20 ns controlled-z gate with a mean fidelity of 99.53%. More than confirming the efficacy of our gate scheme, this high-fidelity result also reveals a promising but rarely explored parameter space uniquely suitable for gate operations between fluxonium qubits.

charge: fluctuation
qubit: entanglement
gate
noise
decoupling
quantum information
microwaves
costs

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