Distinguishing trivial and topological zero-energy states in long nanowire junctions

The emergence of zero-energy states in nontopological superconductors represents an inevitable problem that obscures the proper identification of zero-energy Majorana bound states (MBSs) and prevents their use as topologically protected qubits. In this Research Letter we investigate long superconductor-normal-superconductor junctions where trivial zero-energy states, robust over a large range of parameters, appear as a result of helicity and confinement in the normal region. We demonstrate that both equilibrium supercurrents and critical currents are sensitive to variations in the length of the superconductor regions in the topological phase hosting MBSs but, remarkably, no such length dependence exists when robust, but trivial, zero-energy states are present. This strikingly different response originates from the nonlocal nature of the MBSs, and we therefore propose it as a simple protocol for distinguishing between trivial and topological zero-energy states.