Creating and detecting poor man's Majorana bound states in interacting quantum dots

We theoretically study a system of two quantum dots (QDs) coupled via a third – coupler – QD which is additionally proximitized by an s-wave superconductor. For a wide parameter range, the system can be tuned to sweet spots with a doubly-degenerate ground state, as switches between even- and odd-parity ground states are found to be ubiquitous. The necessary ingredients are a) a finite magnetic field to break the spin degeneracy and b) spin-orbit interaction to mix the spin species. The sweet spots harbor poor man’s Majorana bound states (Phys. Rev. B 86, 134528, 2012) whose quality is quantified by calculating the Majorana polarizations of the degenerate ground states (Phys. Rev. B 101, 125431, 2020). The QDs’ electrochemical potentials are the control knobs utilized to reach the sweet spots and local and non-local conductance calculations could provide a useful map for experimentalists navigating the parameter space. The above system can be realized in a semiconductor 2D electron gas or nanowire with gate- or epitaxially-defined QDs coupled to a grounded superconductor. This work provides a path towards near-future demonstration of nonabelian and non-local Majorana properties, with possible (more long-term) applications in topologically protected quantum computing.