Interfaced Topological States
Credit: Frolov Lab

Hybrid devices hosting material interfaces provide both new functionality and enhanced control through reduced dimensionality. Interfacial systems are among the most promising for realizing Majorana and parafermion zero modes, a key element for realizing intrinsically fault-tolerant topological quantum computing. Topological quantum computing is reliant on braiding these non-Abelian anyons and both the braiding and discovery of these modes requires the development of pristine and highly tailored materials and interfaces. Thrust II assembles integrated expertise focused on realizing topological states by interfacing different classes of materials systems, for example semiconductors with superconductors, superconductors with magnetic systems, and 2D semimetals such as graphene with both other van der Waals materials and with materials grown by molecular beam epitaxy.

This thrust is focused on the discovery and production of pristine one dimensional (nanowire) and two-dimensional hybrid interfaces capable of generating non-Abelian anyons for QIS. Growth, fabrication and characterization techniques developed will exponentially enlarge the set of building blocks for non-Abelian states of matter and to provide a national resource for obtaining these materials. Core materials developed in Thrust 1 will also be leveraged in this effort for interface creation. To perfect and control these interfaces and the emergent states for QIS, MBE-grown III-V and IV-VI semiconductors will be grown and epitaxially interfaced with a variety of superconductors. Combining this with the flexibility of vdW assembly and twistronics opens paths to robust and exotic topological phases. Thrust 2 brings together previously independent tracks of materials development, integrating MBE material from different chambers and with van der Waals systems through a vacuum suitcase network connecting foundry instruments.

Research Highlights

QF Thrust 2 – Year 1 Summary

Year one of the Quantum Foundry was a productive time for Thrust 2 research into Interfaced Topological States, with the production of a variety of novel topological systems, the creation of infrastructure to allow further exploration, and the development of new theoretical models for quantum computation.

The Young lab produced a Chern Insulator by introducing a small but precise twist between layers in stacks of monolayer and bilayer graphene. The rich topological physics of this system means that by applying an electric field, one can switch the direction of the sample’s magnetism, which could be used for magnetic memory. [1] The Palmstrøm and Frolov labs reported new advances in the growth and device studies of superconductor-semiconductor interfaces that are formed between a shell of tin and a semiconductor nanowire. These nanowires have attractive features for robust qubits, in particular, an induced superconducting gap even under relatively high magnetic fields and the preservation of charge parity. [2]

The first year also saw the deployment of new infrastructure, both for stacking arbitrary layered materials into van der Waals heterostructures with clean atomic interfaces and for the growth of ultra-pure epitaxial thin films. Since many interesting topological materials degrade in air, labs in Thrust 2 have built a glovebox system where samples can be fabricated in a chemically benign environment and then transferred to experiments with a system of vacuum suitcases, preventing exposure to oxygen. The Stemmer lab received delivery of a state-of-the-art dual-chamber molecular beam epitaxy system. Once fully commissioned, this system will enable the growth of topological semimetal thin films and heterostructures, whose nontrivial electronic states can be tuned using band structure engineering approaches.

On the theoretical side, a new theory based on gauge symmetry proposes topological qubits made out of superconducting wire arrays, that are better protected from degradation due to environmental conditions. [3] If implemented these arrays could overcome a major hurdle to realistic quantum computation.

[1] Polshyn, H., Zhu, J., Kumar, M.A. et al. Electrical switching of magnetic order in an orbital Chern insulator. Nature 588, 66–70 (2020). https://doi.org/10.1038/s41586-020-2963-8

[2] Pendharkar, M., Zhang, B., Wu, H., Zarassi, A., Zhang, P., Dempsey, C.P., Lee, J.S., Harrington, S.D., Badawy, G., Gazibegovic, S., Jung, J., Chen, A.-H., Verheijen, M.A., Hocevar, M., Bakkers, E.P.A.M., Palmstrøm, C.J., Frolov, S.M. arXiv:1912.06071v1 [cond-mat.mes-hall]

[3] Chamon, C., Green, D. A superconducting circuit realization of combinatorial gauge symmetry. arXiv:2006.10060v1 [quant-ph]