  We analyze the time evolution of a magnetic excitation in a spin-1/2
antiferromagnetic Heisenberg chain after a quantum quench. By a proper
modulation of the magnetic exchange coupling, we prepare a static soliton of
total spin 1/2 as an initial spin state. Using bosonization and a numerical
time dependent density matrix renormalization group algorithm, we show that the
initial excitation evolves to a state composed of two counter-propagating
chiral states, which interfere to yield <S^z> = 1/4 for each mode. We find that
these dynamically generated states remain considerably stable as time evolution
is carried out. We propose spin-Peierls materials and ultracold-atom systems as
suitable experimental scenarios in which to conduct and observe this mechanism.
