  We present a new theoretical treatment of macroscopic quantum self-trapping
(MQST) and quantum coherent atomic tunneling in a zero-temperature two-species
Bose-Einstein condensate system in the presence of the nonlinear
self-interaction of each species, the interspecies nonlinear interaction, and
the Josephson-like tunneling interaction. It is shown that the nonlinear
interactions can dramatically affect the MQST and the atomic tunneling, and
lead to the collapses and revivals (CR) of population imbalance between the two
condensates. The competing effects between the self-interaction of each species
and the interspecies interaction can lead to the quenching of the MQST and the
suppression of the CR and the Shapiro-like steps of the atomic tunneling
current. It is revealed that the interatomic nonlinear interactions can induce
the coherent atomic tunneling between two condensates even though there does
not exist the interspecies Josephson-like tunneling coupling.
