  Topological protection precludes a continuous deformation between
topologically inequivalent configurations in a continuum. Motivated by this
concept, magnetic skyrmions, topologically nontrivial spin textures, are
expected to exhibit the topological stability, thereby offering a prospect as a
nanometer-scale non-volatile information carrier. In real materials, however,
atomic spins are configured as not continuous but discrete distribution, which
raises a fundamental question if the topological stability is indeed preserved
for real magnetic skyrmions. Answering this question necessitates a direct
comparison between topologically nontrivial and trivial spin textures, but the
direct comparison in one sample under the same magnetic fields has been
challenging. Here we report how to selectively achieve either a skyrmion state
or a topologically trivial bubble state in a single specimen and thereby show
how robust the skyrmion structure is in comparison with the bubbles for the
first time. We demonstrate that topologically nontrivial magnetic skyrmions
show longer lifetimes than trivial bubble structures, evidencing the
topological stability in a real discrete system. Our work corroborates the
physical importance of the topology in the magnetic materials, which has
hitherto been suggested by mathematical arguments, providing an important step
towards ever-dense and more-stable magnetic devices.
