Qubits based on merons in magnetic nanodisks

A meron is a classical topological soliton having a half topological charge. It could be materialized in a magnetic disk. However, it will become a quantum mechanical object when its size is of the order of nanometers. Here, we propose to use a nanoscale meron in a magnetic nanodisk as a qubit, where the up and down directions of the core spin are assigned to be the qubit states (0) and (1). We first numerically show that a meron with the radius containing as small as 7 spins can be stabilized in a ferromagnetic nanodisk classically. Then, we show theoretically that universal quantum computation is possible based on merons by explicitly constructing the arbitrary phase-shift gate, Hadamard gate, and CNOT gate. They are executed by applying a magnetic field or spin-polarized current. Our results may be useful for the implementation of quantum computation based on topological spin textures in nanomagnets.