Skyrmion Burst and Multiple Quantum Walk in Thin Ferromagnetic Films

A giant Skyrmion collapses to a singular point by emitting spin waves in a thin ferromagnetic film, when external magnetic field is increased beyond the critical one. The remnant is a single-spin flipped (SSF) point. The SSF point has a quantum diffusion dynamics governed by the Heisenberg model. We determine its time evolution and show the diffusion process is a continuous-time quantum walk. We also analyze an interference of two SSF points after two Skyrmion bursts. Quantum walks for $S=1/2$ and 1 are exact solvable. The system presents a new type of quantum walk for $S>1/2$, where a SSF point breaks into 2S quantum walkers. It is interesting that we can create quantum walkers experimentally at any points in a magnetic thin film, first by creating Skyrmions sequentially and then by letting them collapse simultaneously.