By analogy with the number-difference-phase theory in quantum optics, we in
troduce nonlinear Bose operator to represent the phase across Josephson jun
ction, and build a bosonic operator Josephson qubit model, which establish
itself firmly on the ground of charge state representation and phase state
representation. The operator version of Josephson equations are also obtain
ed. (C) 2001 Elsevier Science B.V. All rights reserved.