Quantum Depinning of a Magnetic Skyrmion

We investigate the quantum depinning of a weakly driven skyrmion out of an impurity potential in a mesoscopic magnetic insulator. For small barrier height, the Magnus force dynamics dominates over the inertial term, and the problem is reduced to a massless charged particle in a strong magnetic field. The universal form of the WKB exponent, the rate of tunneling, and the crossover temperature between thermal and quantum tunneling are provided, independently of the detailed form of the pinning potential. The results are discussed in terms of macroscopic parameters of the insulator Cu_{2}OSeO_{3} and various skyrmion radii. We demonstrate that small enough magnetic skyrmions, with a radius of ∼10 lattice sites, consisting of some thousands of spins, can behave as quantum objects at low temperatures in the millikelvin regime.