A universal quantum gate set for transmon qubits with strong ZZ interactions

• URL: http://arxiv.org/abs/2103.12305v1
• Date: Tue, 23 Mar 2021 04:46:55 GMT
• Title: A universal quantum gate set for transmon qubits with strong ZZ interactions
• Authors: Junling Long, Tongyu Zhao, Mustafa Bal, Ruichen Zhao, George S. Barron, Hsiang-sheng Ku, Joel A. Howard, Xian Wu, Corey Rae H. McRae, Xiu-Hao Deng, Guilhem J. Ribeill, Meenakshi Singh, Thomas A. Ohki, Edwin Barnes, Sophia E. Economou and David P. Pappas
• Abstract summary: High-fidelity single- and two-qubit gates are essential building blocks for a fault-tolerant quantum computer. One limiting factor is the residual ZZ-interaction, which originates from a coupling between computational states and higher-energy states. We experimentally demonstrate that it can be exploited to produce a universal set of fast single- and two-qubit entangling gates.
• Score: 16.56373732567445
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• 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 $t_g=53.8$ 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.

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