Andreev bound states in hybrid superconductor-semiconductor devices
can have near-zero energy in the topologically trivial regime as long as
the confinement potential is sufficiently smooth. These quasi-Majorana
states show zero-bias conductance features in a topologically trivial
phase, mimicking spatially separated topological Majorana states. We
show that in addition to the suppressed coupling between the
quasi-Majorana states, also the coupling of these states across a tunnel
barrier to the outside is exponentially different for increasing
magnetic field. As a consequence, quasi-Majorana states mimic most of
the proposed Majorana signatures: quantized zero-bias peaks, the
4\pi4π
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 quasi-Majorana states for braiding. Therefore, while the appearance
of quasi-Majorana states complicates the observation of topological
Majorana states, it opens an alternative route towards braiding of
non-Abelian anyons and protected quantum computation.
Andreev bound states versus Majorana bound states in quantum dot-nanowire-superconductor hybrid structures: Trivial versus topological zero-bias conductance peaks
