Interferometry and coherent single-electron transport through hybrid superconductor-semiconductor Coulomb islands

Majorana zero modes are leading candidates for topological quantum computation due to their non-local character and non-abelian exchange statistics. Among their attributes, spatially separated Majorana modes are expected to allow coherent single-electron transport through one-dimensional topological superconductors in the Coulomb blockade (CB) regime. We have investigated this feature by patterning an elongated epitaxial InAs-Al Coulomb island embedded in an Aharonov-Bohm interferometer. Using a parallel magnetic field to lower the energy of a discrete sub-gap state in the island below its charging energy, conductance oscillations in the ring were observed with a flux period of h/e (h is Planck’s constant and e is the elementary charge), indicating coherent single-electron transport through the interferometer. Oscillation amplitude was largest when CB conductance peaks in the island were 1e periodic, and suppressed when CB was 2e periodic or when superconductivity was suppressed. Oscillation phase shifts of {\pi} were observed when the charge occupancy of the island was changed by 1e, indicating that the interferometer can detect island parity. Magnetic fields oriented orthogonal to the island reduced the field at which 2e periodic peaks split and where coherent transport could also be observed, suggesting additional non-Majorana mechanisms for 1e transport through these moderately short wires.