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

  1. Marta Pita-Vidal,
  2. Arno Bargerbos,
  3. Rok Žitko,
  4. Lukas J. Splitthoff,
  5. Lukas Grünhaupt,
  6. Jaap J. Wesdorp,
  7. Yu Liu,
  8. Leo P. Kouwenhoven,
  9. Ramón Aguado,
  10. Bernard van Heck,
  11. Angela Kou,
  12. and Christian Kraglund Andersen
Spin qubits in semiconductors are currently one of the most promising architectures for quantum computing. However, they face challenges in realizing multi-qubit interactions over extended distances. Superconducting spin qubits provide a promising alternative by encoding a qubit in the spin degree of freedom of an Andreev level. Such an Andreev spin qubit could leverage the advantages of circuit quantum electrodynamic, enabled by an intrinsic spin-supercurrent coupling. 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 exploit a different qubit subspace, using the spin-split doublet ground state of an electrostatically-defined quantum dot Josephson junction with large charging energy. Additionally, we use a magnetic field to enable direct spin manipulation over a frequency range of 10 GHz. Using an all-electric microwave drive we achieve Rabi frequencies exceeding 200 MHz. We furthermore 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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