A universal quantum gate set for transmon qubits with strong ZZ interactions
Abstract
High-fidelity single- and two-qubit gates are essential building blocks for a fault-tolerant quantum computer. While there has been much progress in suppressing single-qubit gate errors in superconducting qubit systems, two-qubit gates still suffer from error rates that are orders of magnitude higher. One limiting factor is the residual ZZ-interaction, which originates from a coupling between computational states and higher-energy states. While this interaction is usually viewed as a nuisance, here we experimentally demonstrate that it can be exploited to produce a universal set of fast single- and two-qubit entangling gates in a coupled transmon qubit system. To implement arbitrary single-qubit rotations, we design a new protocol called the two-axis gate that is based on a three-part composite pulse. It rotates a single qubit independently of the state of the other qubit despite the strong ZZ-coupling. We achieve single-qubit gate fidelities as high as 99.1% from randomized benchmarking measurements. We then demonstrate both a CZ gate and a CNOT gate. Because the system has a strong ZZ-interaction, a CZ gate can be achieved by letting the system freely evolve for a gate time ns. To design the CNOT gate, we utilize an analytical microwave pulse shape based on the SWIPHT protocol for realizing fast, low-leakage gates. We obtain fidelities of 94.6% and 97.8% for the CNOT and CZ gates respectively from quantum progress tomography.
Cite
@article{arxiv.2103.12305,
title = {A universal quantum gate set for transmon qubits with strong ZZ interactions},
author = {Junling Long and Tongyu Zhao and Mustafa Bal and Ruichen Zhao and George S. Barron and Hsiang-sheng Ku and Joel A. Howard and Xian Wu and Corey Rae H. McRae and Xiu-Hao Deng and Guilhem J. Ribeill and Meenakshi Singh and Thomas A. Ohki and Edwin Barnes and Sophia E. Economou and David P. Pappas},
journal= {arXiv preprint arXiv:2103.12305},
year = {2021}
}