Two electron periodic Coulomb blockade and spin-orbit coupling in hybrid InAs-Al quantum dots*

Proximity induced superconductivity in semiconductors with a strong spin-orbit interaction has recently been the subject of intense theoretical and experimental research, this is driven by the possibility of inducing topological superconductivity. We present measurements of one-dimensional hybrid superconductor-semiconductor quantum dots fabricated on an InAs two dimensional electron gas with an epitaxial Al layer.

We show that in the superconducting state the Coulomb blockade has a two electron periodicity, demonstrating the absence of quasiparticle poisoning. We observe the anti-crossing of spinful sub-gap states in magnetic field, whereby we obtain the spin-orbit direction and, by comparison to a theoretical model, an estimate of the spin-orbit coupling.