  We investigate numerically the tunneling effect under influence of another
particle in a double well system. Such influence from only one degree of
freedom makes decoherence and quantum-classical transition, i.e., suppression
of the tunneling effect. The decoherence happens even for cases that the
influence is from a particle of very small mass, and it has virtually no effect
in the corresponding classical dynamics. There are cases similar to dynamical
localization that the suppressed tunneling rate is several times smaller than
the classical counterpart. This result is relevant for understanding
quantitatively the dynamical process of decoherence and quantum to classical
transition.
