University of Minnesota
School of Physics & Astronomy


Hybrid topological insulator-superconductor devices

Yilikal Ayino
Yilikal Ayino
Richard Anderson

Yilikal Ayino is a graduate student doing condensed matter experiments, working in Vlad Pribiag’s laboratory. Pribiag’s lab is interested in two areas of research, quantum spin transport and Majorana physics in condensed matter systems. The focus is on low dimensional systems – two dimensional electron gases, nanowires, and quantum dots. The group is especially interested in materials that have high spin-orbit coupling, such as Indium antimonide or indium arsenide.

In these materials, the motion of the electrons is strongly tied to their spin state and hence controlling the motion of electrons by applying electric fields allows controlling their spin state. This phenomenon could enable storing and manipulating quantum information encoded in spin-based quantum bits or qubits.

Majorana fermions are predicted fermionic particles, which are their own anti-particles. Following recent theoretical and experimental work, the group is planning to create excitations called Majorana Zero Modes (MZMs). MZMs are expected to play a crucial role in the development of fault-tolerant quantum computers. The material system Pribiag’s group will work with is a two dimensional topological insulator (2D TI) and is based on a hetrostructure of indium arsenide and gallium antimonide. Ayino explains that the heterostructure has a peculiar property, the conduction band of indium arsenide is lower than the valence band of gallium antimonide and with their strong spin-orbit coupling, and this is where the new topological physics begins.

In a 2D TI, the edges act like one dimensional conductors, with electrons of opposite spins propagating in opposite directions. The two dimensional bulk of the material remains insulating. Contacting the 2D TI with a superconductor is predicted to lead to topological superconductivity along the edges. MZM can then be localized at the ends of each edge. Two Majoranas encode a single ordinary fermionic state. Thus, by spatially separating a Majorana pair, it is possible to store a fermionic state nonlocally, making it immune to local perturbations. This protection from local disturbances makes Majoranas an exciting system for reliably storing quantum information. Moreover, bound MZMs may lend themselves to quantum computing circuits that are topologically-protected and subsequently have vanishing error rates. This is a consequence of their predicted non-commutative (non-Abelian) exchange statistics, one of the exotic properties of MZMs which the group will be investigating.