Hydrodynamic equations for mixed quantum states. I. General formulation

Quantum-mechanical hydrodynamic equations are considered for mixed quantum states, and the corresponding equations for pure quantum states are derived as a particular case. A generalization of the "quantum potential" of Bohmian mechanics is formulated. In the mixed-state case, an infinite hierarchy of kinetic equations arises that may be truncated by introducing suitable approximations. The influence of dissipation on the kinetic equations is discussed. (C) 2001 American Institute of Physics.