  The dynamics of the population imbalance of bosons in a double-well potential
is investigated from the point of view of many-body quantum mechanics in the
framework of the two-mode model. For small initial population imbalances,
coherent superpositions of almost equally spaced energy eigenstates lead to
Josephson oscillations. The suppression of tunneling at population imbalance
beyond a critical value is related to a high concentration of initial state
population in the region of the energy spectrum with quasi-degenerate doublets
resulting in imbalance oscillations with a very small amplitude. For
unaccessible long times, however, the system recovers the regime of Josephson
oscillations.
