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# High-fidelity three-qubit iToffoli gate for fixed-frequency superconducting qubits

### Subjects

A Publisher Correction to this article was published on 30 May 2022

## Abstract

The development of noisy intermediate-scale quantum devices has extended the scope of executable quantum circuits with high-fidelity single- and two-qubit gates. Equipping these devices with three-qubit gates will enable the realization of more complex quantum algorithms and efficient quantum error correction protocols with reduced circuit depth. Several three-qubit gates have been implemented for superconducting qubits, but their use in gate synthesis has been limited owing to their low fidelity. Here, using fixed-frequency superconducting qubits, we demonstrate a high-fidelity iToffoli gate based on two-qubit interactions, the so-called cross-resonance effect. As with the Toffoli gate, this three-qubit gate can be used to perform universal quantum computation. The iToffoli gate is implemented by simultaneously applying microwave pulses to a linear chain of three qubits, revealing a process fidelity as high as 98.26(2)%. Moreover, we numerically show that our gate scheme can produce additional three-qubit gates that provide more efficient gate synthesis than the Toffoli and iToffoli gates. Our work not only brings a high-fidelity iToffoli gate to current superconducting quantum processors but also opens a pathway for developing multi-qubit gates based on two-qubit interactions.

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## Data availability

Source data are provided with this paper. All other data that support the findings of this study are available from the corresponding author upon reasonable request.

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## Acknowledgements

We are grateful to J. Wallman and I. Hincks for conversations and insights. This work was funded by the US Department of Energy, Office of Science, Office of Advanced Scientific Computing Research Quantum Testbed Program under contract number DE-AC02-05CH11231.

## Author information

Authors

### Contributions

Y.K. conceived and planned the experiments. Y.K., A.M., and L.B.N. performed the experiments and analysed the data. R.K.N., C.J., and L.C. contributed to the analysis and discussion of the results. J.M.K. fabricated the qubit device. Y.K. wrote the manuscript with assistance from A.M. and L.B.N. All work was carried out under the supervision of D.I.S. and I.S.

### Corresponding author

Correspondence to Yosep Kim.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

## Peer review

### Peer review information

Nature Physics thanks Anton Kockum, Xiao Mi and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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## Supplementary information

### Supplementary Information

Supplementary Notes 1–5 and Figs. 1–9.

## Source data

### Source Data Fig. 2

Statistical source data.

### Source Data Fig. 3

Statistical source data.

### Source Data Fig. 4

Statistical source data.

### Source Data Fig. 5

Statistical source data.

## Rights and permissions

Reprints and Permissions

Kim, Y., Morvan, A., Nguyen, L.B. et al. High-fidelity three-qubit iToffoli gate for fixed-frequency superconducting qubits. Nat. Phys. (2022). https://doi.org/10.1038/s41567-022-01590-3

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• DOI: https://doi.org/10.1038/s41567-022-01590-3