# Coherent spin transport through helical edge states of topological insulator

## TL;DR

This paper investigates how helical edge states in topological insulators can produce spin polarization from unpolarized electrons, with potential applications in quantum computing, demonstrating robust classical and quantum effects influenced by magnetic flux.

## Contribution

It introduces a novel tunneling interferometer based on topological insulator edge states that functions as an ensemble of flux-tunable qubits for quantum computing applications.

## Key findings

- Unpolarized electrons gain polarization after transmission through magnetic impurities.
- The polarization exhibits Aharonov-Bohm resonances with period hc/2e.
- The interferometer operates effectively at high temperatures.

## Abstract

We study coherent spin transport through helical edge states of topological insulator tunnel-coupled to metallic leads. We demonstrate that unpolarized incoming electron beam acquires finite polarization after transmission through such a setup provided that edges contain at least one magnetic impurity. The finite polarization appears even in the fully classical regime and is therefore robust to dephasing. There is also a quantum magnetic field-tunable contribution to the polarization, which shows sharp identical Aharonov-Bohm resonances as a function of magnetic flux - with the period $hc/2e$ - and survives at relatively high temperature. We demonstrate that this tunneling interferometer can be described in terms of ensemble of flux-tunable qubits giving equal contributions to conductance and spin polarization. The number of active qubits participating in the charge and spin transport is given by the ratio of the temperature and the level spacing. The interferometer can effectively operate at high temperature and can be used for quantum calculations. In particular, the ensemble of qubits can be described by a single Hadamard operator. The obtained results open wide avenue for applications in the area of quantum computing.