Dissipation and irreversibility in computing

Abstract

Abstract There has been much discussion for decades over the proper concepts of minimum dissipation per logic gate and what is required for computation, as well as early arguments over logically reversible machines. Here these arguments, and the thermodynamics related to them, are discussed in terms of what is required for a computing machine. This gives a set of requirements for a valid computer that arise already from Turing and a set of limitations on energy dissipation and entropy. Here, the requirements set by Turing on what can and cannot be a computing machine are introduced, and how these limits affect not only the machine, but individual bits and a general need for irreversibility, are discussed. Then, it is shown that there is a minimum dissipation for a bit operation, and this is imposed both by Turing’s requirements as well as by noise in the system. Finally, it is shown that information entropy differs from physical entropy and care must be taken in trying to connect the two quantities. How these requirements, and new ones, affect quantum computation is also discussed.