Delocalized Andreev bound states and non-topological Majorana excitations in InSb nanowiresc

Majorana bound states are zero-energy modes that are created and annihilated by the same operator. They are highly sought after mainly due to their non-abelian statistics, a property desirable both for fundamental research and possible applications in the field of quantum computing. Majorana zero-modes are necessarily spin-less, which directed the attention of their pursuit on the boundary of topological superconductors. Andreev bound states (ABS), however, are spin-full excitations formed when a quantum level is coupled to a superconductor and thus cannot create Majorana modes. A recent proposal showed that it is possible to create a non-local ABS when two spin-less quantum dots are coupled via a superconductor. Following this proposal, we fabricate an InSb nanowire device, in which a short Al strip separates two spin-split quantum dots. 

By measuring the spectrum of the system, we show that we can precisely control the relevant parameters of the system. Finally, by comparing with a theoretical model, we tune the system into a sweet spot where the zero-energy modes are expected to be Majorana excitations.