Realization of an Andreev spin qubit*

Two promising architectures for solid-state quantum information processing are electron spins trapped in semiconductor quantum dots and the collective electromagnetic modes of superconducting circuits. Here we combine these two platforms to realize the Andreev spin qubit, the residual degree of freedom of a quasiparticle trapped in the Andreev levels of a Josephson semiconductor nanowire. The interplay between the spin-orbit coupling in the semiconductor and the superconducting-phase bias results in a spin-split spectrum without an applied Zeeman field. We demonstrate coherent spin manipulation by combining single-shot circuit QED readout and spin-flipping Raman transitions in a naturally occurring Λ system formed by the two spin states and an excited state. We measure a spin-flip time T_S = 17 μs and a spin coherence time T_2E = 52 ns. These results herald a new spin qubit with straightforward circuit QED integration. Moreover, they further our understanding and control of Andreev levels -- the parent states of Majorana zero modes -- in semiconductor-superconductor heterostructures.