  We theoretically study the skyrmion-number dependence of spin-transfer torque
acting on magnetic bubbles. The skymrion number of magnetic bubbles can take
any integer value depending on the magnetic profile on its circumference and
the size of the bubble. We find that the transverse motion of a bubble with
respect to the charge current is greatly suppressed as the absolute value of
skyrmion number departs from unity, whereas the longitudinal motion is less
sensitive.
