Poor Man’s Majorana Tetron

The Majorana tetron is a prototypical topological qubit stemming from the ground-state degeneracy of a superconducting island hosting four Majorana modes. This degeneracy manifests as an effective nonlocal spin degree of freedom, the most paradigmatic signature of which is the topological Kondo effect. Degeneracies of states with different fermionic parities also characterize minimal Kitaev chains, which have lately emerged as a platform to realize and study unprotected versions of Majorana modes, dubbed poor man’sMajorana modes. Here, we introduce the “poor man’sMajorana tetron,” comprising four quantum dots coupled via a floating superconducting island. Its charging energy yields nontrivial correlations among the dots, although, unlike a standard tetron, it is not directly determined by the fermionic parity of the Majorana modes. The poor man’s tetron displays parameter regions with a twofold-degenerate ground state with odd fermionic parity, which gives rise to an effective Anderson impurity model when coupled to external leads. We show that this system can approach a regime featuring the topological Kondo effect under a suitable tuning of experimental parameters. Therefore, the poor man’s tetron is a promising device to observe the nonlocality of Majorana modes and their related fractional conductance.