Abstract
Maintaining or even improving gate performance with growing numbers of parallel controlled qubits is a vital requirement for fault-tolerant quantum computing. For superconducting quantum processors, though isolated one- or two-qubit gates have been demonstrated with high fidelity, implementing these gates in parallel commonly shows worse performance. Generally, this degradation is attributed to various crosstalks between qubits, such as quantum crosstalk due to residual inter-qubit coupling. An understanding of the exact nature of these crosstalks is critical to figuring out respective mitigation schemes and improved qubit architecture designs with low crosstalk. Here we give a theoretical analysis of quantum crosstalk impact on simultaneous gate operations in a qubit architecture, where fixed-frequency transmon qubits are coupled via a tunable bus, and sub-100-ns controlled-Z (cz) gates can be realized by applying a baseband flux pulse on the bus. Our analysis shows that for microwave-driven single-qubit gates, the dressing from the qubit-qubit coupling can cause non-negligible cross-driving errors when qubits operate near frequency collision regions. During cz gate operations, although unwanted nearest-neighbor interactions are nominally turned off, sub-MHz parasitic next-nearest-neighbor interactions involving spectator qubits can still exist, causing considerable leakage or control error when one operates qubit systems around these parasitic resonance points. To ensure high-fidelity simultaneous operations, a request could be raised to figure out a better way to balance the gate error from target qubit systems themselves and the error from nonparticipating spectator qubits. Overall, our analysis suggests that towards useful quantum processors, the qubit architecture should be examined carefully in the context of high-fidelity simultaneous gate operations in a scalable qubit lattice.
- Received 27 October 2021
- Revised 30 December 2021
- Accepted 16 February 2022
DOI:https://doi.org/10.1103/PRXQuantum.3.020301
Published 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 Society
Physics Subject Headings (PhySH)
Popular Summary
Maintaining or even improving gate performance with growing numbers of parallel controlled qubits is a vital requirement for fault-tolerant quantum computing. In today’s superconducting quantum processor, while isolated one- or two-qubit gates have been demonstrated with high fidelity, implementing gate operations in parallel, in general, shows worse gate performance. Generally, this performance degradation is phenomenologically described as the result of various crosstalk effects. The crosstalk effect has been demonstrated as a major error source in today’s multiqubit quantum processors. Thus, an understanding of the exact nature of crosstalk or separating error contributions from different crosstalks is a serious need for figuring out respective mitigation schemes and improved qubit architecture designs with low crosstalk.
The present work gives a theoretical analysis of quantum crosstalk’s impact on simultaneous gate operations in a proposed qubit architecture. It is shown that to suppress quantum crosstalk and ensure high performance, qubit architecture should be examined carefully in the context of high-fidelity simultaneous gate operations. Given this analysis, it is shown how to mitigate quantum crosstalk in the proposed qubit architecture and illustrated that the proposed qubit architecture may be a potential architecture towards large-scale superconducting quantum processors with low quantum crosstalk.
This work is a timely study for improving the understanding of the exact nature of quantum crosstalk and their impact on simultaneous gate operations, thus it may also pave the way for figuring out crosstalk mitigation schemes and improved qubit architecture designs with low crosstalk.
