Abstract
The implementation of high-fidelity swapping operations is of vital importance for executing quantum algorithms on a quantum processor with limited connectivity. We present an efficient pulse-control technique, the cross-cross resonance (CCR) gate, to implement iswap and swap gates with dispersively coupled fixed-frequency transmon qubits. The key to the operation of the CCR gate is the simultaneous driving of both of the coupled qubits at the frequency of another qubit, whereby a fast two-qubit interaction roughly equivalent to ZX+XZ entangling gates is realized without strongly driving the qubits. We develop a calibration technique for the CCR gate and evaluate the performance of the iswap and swap gates. The CCR gate shows remarkable improvements in the average gate error from the conventional decomposition based on the cross-resonance gate.3 MoreReceived 9 June 2021Accepted 19 October 2021DOI:https://doi.org/10.1103/PRXQuantum.2.040336Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum benchmarkingQuantum computationQuantum controlQuantum gatesQuantum Information
Highlights
The number of qubits available in a superconducting quantum processor has been continuously growing despite the restricted connectivity exhibited by square and heavyhexagon lattice structures [1]
We implement iSWAP and SWAP gates consisting of multiple cross-cross resonance (CCR) gates and compare the performance of these gates with the standard gate decomposition based on CR gates
Our theoretical calculations show that iSWAP and SWAP gates implemented with the CCR gate have half the leakage of those implemented with the CR gate for the same gate time
Summary
The number of qubits available in a superconducting quantum processor has been continuously growing despite the restricted connectivity exhibited by square and heavyhexagon lattice structures [1] The connections in these structures are carefully designed to avoid overlapping transition frequencies with neighboring qubits while enabling the implementation of an error-correction code. The additional control lines for the tunable elements may induce an extra degree of interaction with a noisy environment, and such an architecture tends to show shorter coherence times Another class of implementations uses the manipulation of Hamiltonian terms by irradiating a pair of dispersively coupled qubits with microwave pulses [14,15,16,17,18,19]. The calibrated CCR gate demonstrates remarkable improvements in the average gate fidelity, which is confirmed by interleaved randomized benchmarking [28,29,30]
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