Universal quantum computing based on magnetic domain wall qubits

Abstract

Quantum computers allow to solve efficiently certain problems that are intractable for classical computers. For the realization of a quantum computer, a qubit design as the basic building block is a nontrivial starting point. We propose the utilization of nanoscale magnetic domain walls, which are stabilized by achiral energy, as the building blocks for a universal quantum computer made of ferromagnetic racetracks. In contrast to the domain walls stabilized by conventional Dzyaloshinskii-Moriya interactions, these achiral domain walls are bistable and show two degenerate chirality forms. When the domain wall is extremely small, it can be viewed as a quantum mechanical object and the two degenerate chiralities of the domain walls can be used to encode the qubit states $\lvert 0 \rangle$ and $\lvert 1 \rangle$. We show that the single-qubit quantum gates are regulated by magnetic and electric fields, while the Ising exchange coupling facilitates the two-qubit gates. The integration of these quantum gates allows for a universal quantum computation. Our findings demonstrate a promising approach for achieving quantum computing through spin textures that exist in ferromagnetic materials.