It is shown that the minimum energy required to transmit a natural uni
t of information (nat) over a noisy channel is kT, where T is the effe
ctive noise temperature which depends on the interaction between the i
nformation career and the environment. The result follows from the ent
ropy defect principle and general laws of quantum dynamics without any
specific assumptions. (C) 1998 Published by Elsevier Science B.V. All
rights reserved.