  In this paper the macroscopic quantum states of Bose-Einstein condensates in
optical lattices is studied by solving the periodic Gross-Pitaevskii equation
in one-dimensional geometry. It is shown that an exact solution seen to be a
travelling wave of excited macroscopic quantum states resultes in a persistent
atom current which can be controlled by adjusting of the barrier height of the
optical periodic potential. A critical condition to generate the travelling
wave is demonstrated and we moreover propose a practical experiment to realize
the persistent atom current in a toroidal atom waveguide.
