A flux-controlled two-site Kitaev chain

TL;DR

This paper demonstrates how flux and electrostatic control of Andreev bound states in a hybrid device can tune the coupling between quantum dots, facilitating the observation of Majorana bound states in a two-site Kitaev chain.

Contribution

It introduces a method to control ABSs in a flux-tunable Josephson junction, expanding the parameter space for Majorana bound state observation in hybrid devices.

Findings

Extended ABSs enable coupling over 1 μm distance.

Electrostatic and phase control increase MBS observation range.

Spectroscopy reveals Majorana wave function distribution.

Abstract

In semiconducting-superconducting hybrid devices, Andreev bound states (ABSs) can mediate the coupling between quantum dots (QDs), allowing for the realisation of artificial Kitaev chains. In order to engineer Majorana bound states (MBSs) in these systems, one must control the energy of the ABSs. In this work, we show how extended ABSs in a flux tunable Josephson junction can be used to control the coupling between distant quantum dots separated by $\approx$ 1 $\mathrm{\mu}$m. In particular, we demonstrate that the combination of electrostatic control and phase control over the ABSs significantly increases the parameter space in which MBSs are observed. Finally, by employing an additional spectroscopic probe in the hybrid region between the QDs, we gain information about the spatial distribution of the Majorana wave function in a two-site Kitaev chain.