Hybrid Double Quantum Dots: Normal, Superconducting, and Topological Regimes

TL;DR

This paper explores hybrid InAs nanowire double quantum dots with epitaxial Al shells, demonstrating tunable regimes from normal to topological, and providing evidence for Majorana modes through cotunneling peak analysis.

Contribution

It introduces a method to control and identify topological transitions and Majorana modes in hybrid quantum dot devices using magnetic fields and gate voltages.

Findings

Observation of transition from normal to topological regimes.

Detection of weakly hybridized Majorana modes.

Control of inter-dot coupling via side gates.

Abstract

Epitaxial semiconductor-superconductor hybrid materials are an excellent basis for studying mesoscopic and topological superconductivity, as the semiconductor inherits a hard superconducting gap while retaining tunable carrier density. Here, we investigate double-quantum-dot devices made from InAs nanowires with a patterned epitaxial Al two-facet shell that proximitizes two gate-defined segments along the nanowire. We follow the evolution of mesoscopic superconductivity and charging energy in this system as a function of magnetic field and voltage-tuned barriers. Inter-dot coupling is varied from strong to weak using side gates, and the ground state is varied between normal, superconducting, and topological regimes by applying a magnetic field. We identify the topological transition by tracking the spacing between successive cotunneling peaks as a function of axial magnetic field and show that the individual dots host weakly hybridized Majorana modes.