The poor man's Majorana tetron

TL;DR

This paper proposes a simplified quantum dot system called the 'poor man's Majorana tetron' that can exhibit topological Kondo effects, aiding the study of Majorana modes and their non-local properties.

Contribution

It introduces a new minimal device model using quantum dots and a superconducting island to realize and analyze Majorana-like topological phenomena.

Findings

System can exhibit two-fold degenerate ground states with odd fermionic parity.

Potential to observe topological Kondo effect through parameter tuning.

Device offers a platform to study non-locality of Majorana modes.

Abstract

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 non-local spin degree of freedom, whose most paradigmatic signature is the topological Kondo effect. Degeneracies of states with different fermionic parities characterize also minimal Kitaev chains which have lately emerged as a platform to realize and study unprotected versions of Majorana modes, dubbed poor man's Majorana modes. Here, we introduce the ``poor man's Majorana tetron'', comprising four quantum dots coupled via a floating superconducting island. Its charging energy yields non-trivial 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 two-fold degenerate ground state with odd fermionic parity, that 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 non-locality of Majorana modes and their related fractional conductance.