Ehrenfest principle and unitary dynamics of quantum-classical systems   with general potential interaction
  Representation of classical dynamics by unitary transformations has been used to develop unified description of hybrid classical-quantum systems with particular type of interaction, and to formulate abstract systems interpolating between classical and quantum ones. We solved the problem of unitary description of two interpolating systems with general potential interaction. The general solution is used to show that with arbitrary potential interaction between the two interpolating systems the evolution of the so called unobservable variables is decoupled from that of the observable ones if and only if the interpolation parameters in the two interpolating systems are equal. 
M. Radonjic, D.B. Popovic, S. Prvanovic and N. Buric
quant-ph