Tracking the location of Majorana states bound to Josephson vortices in S/TI/S junctions by Scanning SQUID Microscopy

It is predicted that Majorana bound states (MBS) emerge on the surface of a topological insulator proximitized by a conventional s-wave superconductor. In a Superconductor-Topological Insulator-Superconductor (S-TI-S) Josephson junction, the MBS are localized at the cores of Josephson vortices where the phase difference across the junction is an odd-multiple of π. They can be manipulated by applying fields and currents to carry out braiding operations for quantum information processing. The position and motion of these vortices may be tracked with local magnetic imaging. We are developing a Scanning SQUID Microscope (SSM) in which the probe is a submicron superconducting pickup loop inductively-coupled to a commercial dc SQUID, providing the required field sensitivity and spatial resolution. In this talk, we report our progress towards cooling down our SSM in a dry dilution refrigerator and imaging the Josephson vortices and the currents carried by the Majorana states in S-TI-S devices.