Quantum information processing: The case of vanishing interaction energy
  We investigate the rate of operation of quantum "black boxes" ("oracles") and point out the possibility of performing an operation by a quantum "oracle" whose average energy equals zero. This counterintuitive result not only presents a generalization of the recent results of Margolus and Levitin, but might also sharpen the conceptual distinction between the "classical" and the "quantum" information. 
M. Dugic and M.M. Cirkovic