University of Minnesota
School of Physics & Astronomy


Towards Topological Quantum Computing

Vlad Pribiag
Vlad Pribiag
Richard Anderson

Vlad Pribiag is a condensed matter experimental physicist. His research focuses on novel low-dimensional semiconductors. He is particularly interested in materials with strong spin-orbit coupling, studying how the unique properties of certain materials can be used for information processing. Spin orbit coupling refers to the interaction between a particle’s spin and its motion. Physicists can control the spin by manipulating the motion of the particle. Physicists have found ways to encode either classical information or quantum information in the spin.

At the moment, Pribiag focuses on two different types of materials. The first are semiconductor nanowires, a few microns in length and about a hundred nanometers in diameter, which can be grown with perfect crystal structure, something very hard to do in a three dimensional crystal. The second type is a 2D topological insulator (2D TI), a material system based on conventional semiconductors, but with truly unique properties. The bulk of a 2D TI is insulating, with edges that, under certain conditions, will conduct electricity. The idea is to get current to flow along the edges, which are spin polarized: one spin flows clockwise and another counterclockwise, in parallel channels. Pribiag says these edge modes exhibit very strong spin orbit coupling.

Currently, Pribiag is interested in hybrid devices that combine 2D TIs and superconductors to create Majorana modes. These modes share many similarities with Majorana fermions, particles which are their own antiparticles that were first theorized by Ettore Majorana in 1937. Pribiag says that studying the physics of Majorana modes is interesting in connection to Majorana’s theory, and they are also of great interest for quantum information processing. “It’s almost like splitting an electron in two and, because this electron is now nonlocal, it can provide a robust way to store information.” A key goal of quantum computing is to be able to store quantum information for a long period without corruption. Local perturbations might affect one of the Majoranas in each pair, but because they are unlikely to affect both, the quantum information would be preserved. It’s the properties of the pair that matter in this situation.

It also turns out that Majoranas have interesting quantum mechanical properties when you exchange them in space, something called a non-Abelian anyon. An anyon is a type of particle that exists only in low-dimensional systems, which has different properties than usual fermions and bosons. Usually, exchanging the positions of several anyons can be done in any order, resulting in the same final quantum state. With non-Abelian anyons, the order matters. “With Abelian anyons, you get a phase change when you swap them, but non-Abelian anyons will create twists. Think of it as braiding threads. The braiding changes the final state of the system.” Braiding of Majoranas has applications in topological quantum computing, which aims to realize very accurate quantum operations.

Pribiag is a new faculty member at the School and is currently in the midst of building nanodevices for use in his experiments. His plan is to cool the devices down to 10 milli-Kelvin and measure the electronic transport in these systems.