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Poor Man’s Majorana Tetron

Maximilian Nitsch1,*,†, Lorenzo Maffi2,3,*, Virgil V. Baran4,5,6, Rubén Seoane Souto7, Jens Paaske6, Martin Leijnse1, and Michele Burrello6,8,9,‡

  • *These authors contributed equally to this work.
  • †Contact author: maximilian.nitsch@ftf.lth.se
  • ‡Contact author: michele.burrello@unipi.it
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PRX Quantum 6, 030365 – Published 29 September, 2025

DOI: https://doi.org/10.1103/r75t-jv32

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 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’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 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.

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Popular Summary

Over the past decade, the quest to understand and control emergent quantum phenomena has led researchers to engineer hybrid devices that combine the excellent level of control of semiconductors with the coherence effects of superconductors. These systems offer a route to realize the so-called Majorana modes, the simplest example of non-Abelian anyons predicted to display nonlocal correlations that can be harnessed for future quantum technologies. To this end, recent experiments have realized a family of devices called minimal Kitaev chains: systems composed of two quantum dots that enable the study of Majorana modes in highly tunable architectures.

A central challenge remains to move beyond these minimal devices and probe the nonlocal properties of Majorana modes. One defining signature of Majorana nonlocality is the topological Kondo effect, a transport phenomenon that emerges when at least four Majorana modes in a floating device are connected to multiple external leads.

This work provides a blueprint for a minimal setup that we dub poor man’s Majorana tetron, consisting of four quantum dots linked by a floating superconducting island. This geometry enables the realization of quantum states that share the same correlations of four Majorana modes. Therefore, it provides a variant of the simplest topological qubit—the tetron—characterized by a trade-off of its topological protection for enhanced controllability.

We determine realistic conditions to obtain poor man’s Majorana tetrons that display degenerate ground states. This poses the basis for the observation of the topological Kondo effect with materials and techniques available in state-of-the-art experiments and opens up the path toward the exploration of new quantum many-body critical phenomena.

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PRX Quantum 6, 030365– Published 29 September, 2025
  • Received 3 December 2024
  • Revised 2 May 2025
  • Accepted 23 July 2025
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