Kitaev chain in an alternating quantum dot-Andreev bound state array

TL;DR

This paper proposes a simplified implementation of a Kitaev chain using an array of alternating quantum dots and hybrid segments, enabling tunable couplings and potential topological protection for Majorana modes.

Contribution

It introduces a novel setup combining normal and hybrid quantum dots to realize a Kitaev chain with tunable couplings and reduced complexity.

Findings

Two-site Kitaev chain feasible with one quantum dot and one hybrid segment.

Scaling to three sites introduces next-nearest-neighbor couplings.

Longer chains mitigate energy splitting, approaching topological protection.

Abstract

We propose to implement a Kitaev chain based on an array of alternating normal and superconductor hybrid quantum dots embedded in semiconductors. In particular, the orbitals in the dot and the Andreev bound states in the hybrid are now on equal footing and both emerge as low-energy degrees of freedom in the Kitaev chain, with the couplings being induced by direct tunneling. Due to the electron and hole components in the Andreev bound state, this coupling is simultaneously of the normal and Andreev types, with their ratio being tunable by varying one or several of the experimentally accessible physical parameters, e.g., strength and direction of the Zeeman field, as well as changing proximity effect on the normal quantum dots. As such, it becomes feasible to realize a two-site Kitaev chain in a simple setup with only one normal quantum dot and one hybrid segment. Interestingly, when scaling up the system to a three-site Kitaev chain, next-nearest-neighbor couplings emerge as a result of high-order tunneling, lifting the Majorana zero energy at the sweet spot. This energy splitting is mitigated in a longer chain, approaching topological protection. Our proposal has two immediate advantages: obtaining a larger energy gap from direct tunneling and creating a Kitaev chain using a reduced number of quantum dots and hybrid segments.