Auto-tuning, manipulation and braiding of topological quantum bits in tapered nanowire networks

Project Information

TopoTapered

Grant agreement ID: 101067680

DOI

10.3030/101067680

Project terminated on 7 April 2025

EC signature date 27 February 2023

Start date 1 August 2023

End date 31 July 2025

Funded under

• European Research Council (ERC)

Total cost

No data

EU contribution

€ 150 000,00

Coordinated by

WEIZMANN INSTITUTE OF SCIENCE
Israel

Periodic Reporting for period 1 - TopoTapered (Auto-tuning, manipulation and braiding of topological quantum bits in tapered nanowire networks)

Reporting period: 2023-08-01 to 2025-07-31

Summary of the context and overall objectives of the project

The goal of the TopoTapered PoC project was to establish tapered nanowires as a viable, robust technology to auto-tune Majorana zero modes (MZMs), transport, and braid them towards quantum computation. The formation of MZMs in quasi-one dimensional semiconducting nanowires necessitates satisfying multiple conditions: The semiconductor has strong spin-orbit coupling; The chemical potential is tuned sufficiently close to the Kramer’s degeneracy throughout the topological segment (sufficiently low disorder); The induced superconducting gap is larger than the Zeeman gap opened by a properly aligned magnetic field; Spatial manipulation of the MZMs has to be adiabatic to remain in the topological groundstate. Tapered nanowires assist in achieving two of these requirements: Tapering modulates the subband quantization along the nanowires and with it the energy of the Kramer’s degeneracy such that they cross the chemical potential at segments along the nanowire without global fine tuning; Application of a global backgate results in sliding of the induced topological segments enabling continuous adiabatic transportation of the MZMs.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We have successfully demonstrated the advantage of tapered nanowires in tuning their spectroscopic properties. We have grown tapered nanowires with a diameter that gradually varies along the nanowire axis. We have imaged the quasi-local spectroscopy of the electronic subbands using scanning tunneling microscopy.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The main challenge towards the implementation of our technology has remained the convincing and robust demonstration of MZMs in such hybrid semiconducting-superconducting nanowire systems, which is a prerequisite for the implementation of tapering.

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