  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.
