Probing the topology of the quantum analog of a classical skyrmion

The standard theory of magnetic skyrmions essentially relies on the assumption that the local magnetization is a classical vector. In this paper, the authors introduce a novel quantum skyrmion state, and show that this quantum analog of a classical skyrmion can be fully characterized by a local operator defined on three neighboring sites, the quantum scalar chirality. They show that this observable is nearly constant inside the quantum skyrmion phase and can thus be used as an effective topological invariant.