Nanocomputers: Theoretical Models

Encyclopedia of Nanoscience and Nanotechnology www.aspbs.com/enn Nanocomputers: Theoretical Models Michael P. Frank University of Florida, Gainesville, Florida, USA CONTENTS 1. Introduction 2. Fundamental Physics of Computing 3. Traditional Models of Computation 4. New Models of Nanocomputers 5. Generic Realistic Model of Nanocomputers 6. Specific Nanocomputing Technology Proposals 7. Conclusion Glossary References 1. INTRODUCTION In this chapter, we survey a variety of aspects of theoretical models of computation, with an emphasis on those modeling issues that are particularly important for the engineering of efficient nanoscale computers. Most traditional models of computing (such as those treated in Savage’s textbook [1]) ignore a number of important fundamental physical effects that can dramatically impact computational performance at the nanoscale, such as the basic thermodynamic limits on information processing [2], and the possibility of utilizing quantum physical superpositions (essentially, weighted combinations) of logic states [3]. New, alternative models of computing that allow reversible computing [4], while respecting the laws of thermodynamics may (gradually, over the next ∼50 years) achieve a level of performance and cost efficiency on all types of computational tasks that is literally thousands of times greater than the best that is physically possible using conventional irreversible models [5]. Also, those models that are not only reversible but also allow coherent quantum computing, based on self-interference of entangled superpositions of states, furthermore permit expressing algorithms (for at least some special-purpose problems) that require exponentially fewer steps in these models than the best known algorithms in the older models that do not [3]. Because of such discrepancies, the scope and precision of our models of computation must be rev