Integrating micromagnets and hybrid nanowires for topological quantum computing

Malcolm Jardine,Wenbo Wang,Ania C Bleszynski Jayich,Yifan Jiang,John Stenger,Eline J De Jong,Sergey Frolov

doi:10.21468/scipostphys.11.5.090

Abstract

Majorana zero modes are expected to arise in semiconductor-superconductor hybrid systems, with potential topological quantum computing applications. One limitation of this approach is the need for a relatively high external magnetic field that should also change direction at the nanoscale. This proposal considers devices that incorporate micromagnets to address this challenge. We perform numerical simulations of stray magnetic fields from different micromagnet configurations, which are then used to solve for Majorana wavefunctions. Several devices are proposed, starting with the basic four-magnet design to align magnetic field with the nanowire and scaling up to nanowire T-junctions. The feasibility of the approach is assessed by performing magnetic imaging of prototype patterns.

Highlights

We look beyond to explore how generating local magnetic fields using micromagnets can aid in the design of Majorana devices
The stray magnetic fields are integrated over an imagined hexagonal nanowire cross-section to obtain a one-dimensional field profile which can in principle extend to infinity
The strips are written by electron beam lithography (EBL) and the metal is deposited by electron beam evaporation from a CoFeB source to a thickness of 20 nm

Summary

Introduction

One-dimensional topological superconductors host Majorana zero modes (MZMs) [1,2]. They are promising for fault-tolerant quantum computing because of the predicted topological protection that they facilitate [3, 4]). One class of ideas has focused on generating synthetic spin-orbit coupling in weak spin-orbit materials through nanomagnet patterning [11,12,13,14,15,16,17,18] Another class imagines shells of magnetic insulators on nanowires as a path to topological superconductivity through using exchange interactions [19, 20]. Inducing magnetic fields avoids the reliance on a global magnetic field, and fields can be oriented differently in the nanowire set-up opening up possibilities in measuring of complicated structures like T-junctions braiding devices and the ability to address and manipulate individual MZMs. In the basic building block (Dragonfly, Fig. 1), four micromagnets are arranged around the nanowire such that field lines flow along the wire for 700 nm. Find that it is possible to realize the building block Dragonfly configurations, though arranging all micromagnets in a T-junction to the desired orientations will require very accurate control of switching fields

Numerical Results

Magnetic Force Microscopy

Background on Majorana nanowire model