  We consider the properties of stationary states and the dynamics of
Bose-Einstein condensates (BECs) in a double-well (DW) potential with pair
tunneling by using a full quantum-mechanical treatment. Furthermore, we study
the quantum quench dynamics of the DW system subjected to a sudden change of
the Peierls phase. It is shown that strong pair tunneling evidently influences
the energy spectrum structure of the stationary states. For relatively weak
repulsive interatomic interactions, the dynamics of the DW system with a
maximal initial population difference evolves from Josephson oscillations to
quantum self-trapping as one increases the pair tunneling strength, while for
large repulsion the strong pair tunneling inhibits the quantum self-trapping.
In the case of attractive interatomic interactions, strong pair tunneling tends
to destroy the Josephson oscillations and quantum self-trapping, and the system
eventually enters a symmetric regime of zero population difference. Finally,
the effect of the Peierls phase on the quantum quench dynamics of the system is
analyzed and discussed. These new features are remarkably different from the
usual dynamical behaviors of a BEC in a DW potential.
