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Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit

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Abstract

Spin qubits in semiconductors are a promising platform for producing highly scalable quantum computing devices. However, it is difficult to realize multiqubit interactions over extended distances. Superconducting spin qubits provide an alternative by encoding a qubit in the spin degree of freedom of an Andreev level. These Andreev spin qubits have an intrinsic spin–supercurrent coupling that enables the use of recent advances in circuit quantum electrodynamics. The first realization of an Andreev spin qubit encoded the qubit in the excited states of a semiconducting weak link, leading to frequent decay out of the computational subspace. Additionally, rapid qubit manipulation was hindered by the need for indirect Raman transitions. Here we use an electrostatically defined quantum dot Josephson junction with large charging energy, which leads to a spin-split doublet ground state. We tune the qubit frequency over a frequency range of 10 GHz using a magnetic field, which also enables us to investigate the qubit performance using direct spin manipulation. An all-electric microwave drive produces Rabi frequencies exceeding 200 MHz. We embed the Andreev spin qubit in a superconducting transmon qubit, demonstrating strong coherent qubit–qubit coupling. These results are a crucial step towards a hybrid architecture that combines the beneficial aspects of both superconducting and semiconductor qubits.

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Fig. 1: ASQ.
Fig. 2: Coherent manipulation of the ASQ.
Fig. 3: Coherence of the ASQ.
Fig. 4: Coherent ASQ–transmon coupling.

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Data availability

The data that support the findings of this study are publicly available via 4TU.ResearchData at https://doi.org/10.4121/c.6073271.

Code availability

The analysis code that supports the findings of this study is publicly available via 4TU.ResearchData at https://doi.org/10.4121/c.6073271.

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Acknowledgements

We acknowledge fruitful discussion with M. Veldhorst, M. Russ, F. Malinowski, V. Fatemi and Y. Nazarov. We further thank P. Krogstrup for guidance in the material growth. This research was inspired by prior work by J.J.W. where the spin-flip transition in an InAs/Al nanowire weak link was directly observed in spectroscopy under the application of a magnetic field29. This research is co-funded by the allowance for Top Consortia for Knowledge and Innovation (TKI) from the Dutch Ministry of Economic Affairs; research project ‘Scalable circuits of Majorana qubits with topological protection’ (i39, SCMQ) with project no. 14SCMQ02; the Dutch Research Council (NWO); and the Microsoft Quantum initiative. R.Ž. acknowledges support from the Slovenian Research Agency (ARRS) under P1-0416 and J1-3008. R.A. acknowledges support from the Spanish Ministry of Science and Innovation through grant PGC2018-097018-B-I00 and from the CSIC Research Platform on Quantum Technologies PTI-001. B.v.H. and C.K.A. acknowledge support from the Dutch Research Council (NWO).

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Contributions

A.B., M.P.-V. and A.K. conceived the experiment. Y.L. developed and provided the nanowire materials. A.B., M.P.-V., L.J.S., L.G. and J.J.W. prepared the experimental setup and data acquisition tools. L.J.S. deposited the nanowires. A.B. and M.P.-V. designed and fabricated the device, performed the measurements and analysed the data, with continuous feedback from L.J.S., L.G., J.J.W., B.v.H., A.K. and C.K.A. R.A., B.v.H. and R.Ž. provided theory support during and after the measurements. A.B., M.P.-V. and B.v.H. wrote the code to compute the circuit energy levels and extract the experimental parameters. L.P.K., R.A., B.v.H., A.K. and C.K.A. supervised the work. A.B., M.P.-V. and C.K.A. wrote the paper with feedback from all authors.

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Correspondence to Marta Pita-Vidal or Christian Kraglund Andersen.

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Pita-Vidal, M., Bargerbos, A., Žitko, R. et al. Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit. Nat. Phys. 19, 1110–1115 (2023). https://doi.org/10.1038/s41567-023-02071-x

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