Energy Barriers, Demons, and Minimum Energy Operation of Electronic Devices

摘要

The presence of thermal noise dictates that an energy barrier is needed to preserve a binary state. Therefore, all electronic devices contain at least one energy barrier to control electron flow. The barrier properties, such as height, length, and shape determine the operating characteristics of electronic devices. Furthermore, changes in the barrier shape require changes in charge density/distribution. Operation of all charge transport devices includes charging/discharging capacitances to change barrier height. In this paper we analyze energy dissipation for several schemes of charging capacitors. A basic assumption of Reversible Computing is that the computing system is completely isolated from the thermal bath, i. e., phonons are not coupled to the motion of the information-bearing particle. An isolated system is a mathematical abstraction never perfectly realized in practice. Coupling of the system to the rest of the world results in thermal noise and errors due to thermal excitations are equivalent to information erasure, and thus computation dissipates energy. Another source of energy dissipation is due to the need of measurement and control. To analyze this side of the problem, the Maxwell's Demon is a useful abstraction. Proposals for "adiabatic circuits" do not make attempts to isolate the system from the thermal bath, hence the circuits cannot be reversible. We hold that apparent "energy savings" in models of adiabatic circuits result from neglecting the total energy needed by other parts of the system to implement the circuit. We are not aware of convincing experimental evidences that adiabatic circuits save wall-plug energy.