Dynamics and manipulation of a trapped, superconducting quasiparticle: Part 2/2*

The physics of conventional and exotic superconductors can be probed through their microscopic quasiparticle excitations. Recent advances in mesoscopic superconductor-semiconductor devices have created the opportunity to measure and control such excitations, such as Majorana zero modes in a topological superconductor regime. Here, our mesoscopic device is a Josephson element with an InAs nanowire weak link. Due to spin-orbit coupling in the nanowire, the spin states of a single quasiparticle trapped in the junction’s Andreev levels exhibit microwave-accessible energy splittings without an applied magnetic (Zeeman) field. This “superconducting spin” is readily coupled to a microwave resonator via its spin-dependent supercurrent. We will present our experimental platform demonstrating large spin-dependent dispersive shifts of a microwave resonator. We achieve single-shot, quantum-non-demolition readout of the spin as well as coherent manipulation of the quasiparticle state. We will discuss the real-time dynamics of the quasiparticle, which have implications for Majorana devices and Andreev spin qubits. In this second part of a joint presentation, we will describe the experimental data and discuss its outlook.