I. Introduction
Energy loss is an important consideration in digital design. Part of the problem of energy dissipation is related to nonideality of switches and materials. Higher levels of integration and the use of new fabrication processes have dramatically reduced the heat loss over the last decades. The other part of the problem arises from Landauer's principle [9] for which there is no solution. Landauer's principle states that logic computations that are not reversible, necessarily generate heat for every bit of information that is lost, where is Boltzmann's constant and the temperature. For room temperature the amount of dissipating heat is small (i.e., ), but not negligible. The design that does not result in information loss is called reversible. It naturally takes care of heating generated due to the information loss. This will become an issue as the circuits become smaller.