Probing Majorana localization in minimal Kitaev chains through a quantum dot

TL;DR

This paper proposes using an extra quantum dot coupled to a minimal Kitaev chain to reliably identify Majorana bound states through tunneling spectroscopy, distinguishing true Majoranas from trivial zero-energy states.

Contribution

Introducing an additional quantum dot as a diagnostic tool to detect spatially separated Majorana states in minimal Kitaev chains, enhancing experimental identification methods.

Findings

Extra dot coupling splits even-odd degeneracy at Majorana sweet spots.

Persistent degeneracy indicates well-separated Majorana states.

Conductance patterns can differentiate Majorana states from trivial crossings.

Abstract

Artificial Kitaev chains, formed by quantum dots coupled via superconductors, have emerged as a promising platform for realizing Majorana bound states. Even a minimal Kitaev chain (a quantum dot--superconductor--quantum dot setup) can host Majorana states at discrete sweet spots. However, unambiguously identifying Majorana sweet spots in such a system is still challenging. In this work, we propose an additional dot coupled to one side of the chain as a tool to identify good sweet spots in minimal Kitaev chains. When the two Majorana states in the chain overlap, the extra dot couples to both and thus splits an even--odd ground-state degeneracy when its level is on resonance. In contrast, a ground-state degeneracy will persist for well-separated Majorana states. This difference can be used to identify points in parameter space with spatially separated Majorana states, using tunneling spectroscopy measurements. We perform a systematic analysis of different relevant situations. We show that the additional dot can help distinguishing between Majorana sweet spots and other trivial zero-energy crossings. We also characterize the different conductance patterns, which can serve as a guide for future experiments aiming to study Majorana states in minimal Kitaev chains.