Adiabatic nonabelian braiding of imperfect Majoranas

Abstract: Demonstration of a nontrivial result of quasiparticle exchange (or braiding) is usually considered the definitive proof of a topological phase with nonabelian excitations, such as Majorana bound states (MBSs). However, in finite systems with disorder and smooth potential variations, the MBSs are imperfect in the sense that they are not fully isolated in space and can, to a varying degree, resemble conventional fermions. Here, we study the braiding properties of isolated MBSs, regular fermions, and anything in between. We find a way to compensate for the undesired splitting of the ground-state degeneracy which occurs during the protocol for imperfect MBS. This leads to a braiding outcome that depends on the degree of MBS isolation but remains robust and nonabelian except in the perfect fermion limit. Our protocol could be implemented in different platforms with nonabelian excitations, including quantum-dot-based minimal Kitaev chains.