Andreev spin relaxation time in a shadow-evaporated InAs weak link

Spin qubits and superconducting qubits are prominent prospective solid-state platforms for quantum computing. Andreev spin states merge these platforms microscopically by existing in Josephson weak links in semiconductor nanowires. Andreev spins can be coupled to superconducting circuits directly via spin-dependent supercurrent, opening new possibilities for fast readout and long-range coupling of spin qubits. By using a resonator with an intermediate strength of inductive coupling, we probed spin states directly, without virtual interactions to higher orbital states and without a transmon-like circuit. We measured the relaxation time of an Andreev spin in a shadow-evaporated InAs weak link, finding comparable performance to etched nanowires and correlations of the relaxation time with the excitation spectrum. Our work raises questions about sources of energy relaxation in InAs-based Andreev spin qubits, and demonstrates a circuit design that is translatable to other materials platforms.