Adriaan Vuik, Bas Nijholt, Anton R. Akhmerov, Michael Wimmer
SciPost Phys. 7, 061 (2019) ·
published 12 November 2019

· pdf
Andreev bound states in hybrid superconductorsemiconductor devices can have
nearzero energy in the topologically trivial regime as long as the confinement
potential is sufficiently smooth. These quasiMajorana states show zerobias
conductance features in a topologically trivial phase, mimicking spatially
separated topological Majorana states. We show that in addition to the
suppressed coupling between the quasiMajorana states, also the coupling of
these states across a tunnel barrier to the outside is exponentially different
for increasing magnetic field. As a consequence, quasiMajorana states mimic
most of the proposed Majorana signatures: quantized zerobias peaks, the $4\pi$
Josephson effect, and the tunneling spectrum in presence of a normal quantum
dot. We identify a quantized conductance dip instead of a peak in the open
regime as a distinguishing feature of true Majorana states in addition to
having a bulk topological transition. Because braiding schemes rely only on the
ability to couple to individual Majorana states, the exponential control over
coupling strengths allows to also use quasiMajorana states for braiding.
Therefore, while the appearance of quasiMajorana states complicates the
observation of topological Majorana states, it opens an alternative route
towards braiding of nonAbelian anyons and protected quantum computation.