Information Processing with Electron Spins

Information processors process information in a variety of ways. The human brain processes information through a highly interconnected system of neurons and synapses, while a digital computer processes information by having a binary switch toggle on and off in response to a stream of binary bits. The “switch” is the most primitive unit of the modern computer. The better it is (faster, more energy efficient, more reliable, etc.), the more advanced is the computer hardware. Energy efficiency, however, is more important than any other attribute, not so much because energy is costly, but because too much energy dissipation prevents increasing the density of switches on a chip that is necessary to make the chip increasingly more powerful. Reducing dissipation entails radically new and often revolutionary approaches for implementing the switch. One such approach is to encode digital bit information in the spin polarization of a single electron (or ensemble of electrons) and then using two mutually antiparallel polarizations to represent the binary bits 0 and 1. Switching between the bits can be accomplished by simply flipping the polarizations of the spins, which takes very little energy. Such switches are extremely energy efficient if designed properly, but they are somewhat slower than traditional transistor-based switches and can be more error prone. This paper discusses the pros and cons of spin-based switches and introduces the reader to the most recent advancements in information processing predicated on encoding information in electron spin polarization.