Theory of three-terminal Andreev spin qubits

In this Letter, we introduce a next generation of Andreev spin qubits—three-terminal Andreev spin qubits. These qubits outperform two-terminal devices in the speed of two-qubit gates, benefiting from enhanced spin splitting. Our theoretical analysis reveals increased tunability and interqubit coupling mediated by the supercurrent. Furthermore, it provides a comprehensive explanation for the results of a recent experiment on a three-terminal device [M. Coraiola et al., Phys. Rev. X 14, 031024 (2024)]. We identify the optimal operational regime for single- and two-qubit gates. Moreover, our concise theoretical framework for the equilibrium multiterminal Josephson effect offers significant potential for exploring nontrivial physics in the artificial dimensions of superconducting phase differences–—a rapidly growing field of research.