  Recent experiments have reported on controlled nucleation of individual
skyrmions in chiral magnets. Here we show that in magnetic ultra-thin films
with interfacial Dzyaloshinskii-Moriya interaction, single skyrmions of
different radii can be nucleated by creating a local distortion in the magnetic
field. In our study, we have considered zero temperature quantum nucleation of
a single skyrmion from a ferromagnetic phase. The physical scenario we model is
one where a uniform field stabilizes the ferromagnet, and an opposing local
magnetic field over a circular spot, generated by the tip of a local probe,
drives the skyrmion nucleation. Using spin path integrals and a collective
coordinate approximation, the tunneling rate from the ferromagnetic to the
single skyrmion state is computed as a function of the tip's magnetic field and
the circular spot radius. Suitable parameters for the observation of the
quantum nucleation of single skyrmions are identified.
