  The locomotion and design of microswimmers are topical issues of current
fundamental and applied research. In addition to numerous living and artificial
active microswimmers, a passive microswimmer was identified only recently: a
soft, Lambda-shaped, non-buoyant particle propagates in a shaken liquid of
zero-mean velocity [Jo et al. Phys. Rev. E 94, 063116 (2016)]. We show that
this novel passive locomotion mechanism works for realistic non-buoyant,
asymmetric Janus microcapsules as well. According to our analytical
approximation, this locomotion requires a symmetry breaking caused by different
Stokes drags of soft particles during the two half periods of the oscillatory
liquid motion. It is the intrinsic anisotropy of Janus capsules and
Lambda-shaped particles that break this symmetry for sinusoidal liquid motion.
Further, we show that this passive locomotion mechanism also works for the
wider class of symmetric soft particles, e.g., capsules, by breaking the
symmetry via an appropriate liquid shaking. The swimming direction can be
uniquely selected by a suitable choice of the liquid motion. Numerical studies,
including lattice Boltzmann simulations, also show that this locomotion can
outweigh gravity, i.e., non-buoyant particles may be either elevated in shaken
liquids or concentrated at the bottom of a container. This novel propulsion
mechanism is relevant to many applications, including the sorting of soft
particles like healthy and malignant (cancer) cells, which serves medical
purposes, or the use of non-buoyant soft particles as directed microswimmers .
