Kitaev chain with a quantum dot

TL;DR

This paper analytically studies a finite Kitaev chain coupled to a quantum dot, revealing robust Andreev bound states in the trivial phase that mimic Majorana zero modes, impacting interpretations of experimental signatures.

Contribution

It provides an analytical solution showing the emergence of ABS in a Kitaev chain with a quantum dot, highlighting their robustness and similarity to MZMs in measurements.

Findings

Robust ABS appear in the trivial phase due to partial decoupling of MBSs.

ABS signatures in tunneling measurements mimic those of MZMs.

The solution bridges the Kitaev chain model with realistic quantum dot-superconductor systems.

Abstract

We solve analytically the problem of a finite length Kitaev chain coupled to a quantum dot (QD), which extends the standard Kitaev chain problem making it more closely related to the quantum dot-semiconductor-superconductor (QD-SM-SC) nanowire heterostructure that is currently under intense investigation for possible occurrence of Majorana zero modes (MZMs). Our analytical solution reveals the emergence of a robust Andreev bound state (ABSs) localized in the quantum dot region as the generic lowest energy solution in the topologically trivial phase. By contrast, in the bare Kitaev chain problem such a solution does not exist. The robustness of the ABS in the topologically trivial phase is due to a partial decoupling of the component Majorana bound states (MBSs) over the length of the dot potential. As a result, the signatures of the ABS in measurements that couple locally to the quantum dot, e.g., tunneling measurements, are identical to the signatures of topologically-protected MZMs, which arise only in the topological superconducting (TS) phase of the Kitaev chain.