  We consider a system of two semifluxons of opposite polarity in a 0-pi-0 long
Josephson junction, which classically can be in one of two degenerate states:
up-down or down-up. When the distance $a$ between the 0-pi boundaries
(semifluxon's centers) is a bit larger than the crossover distance $a_c$, the
system can switch from one state to the other due to thermal fluctuations or
quantum tunneling. We map this problem to the dynamics of a single particle in
a double well potential and estimate parameters for which quantum effects
emerge. We also determine the classical-to-quantum crossover temperature as
well as the tunneling rate (energy level splitting) between the states up-down
and down-up.
