Quantum Cellular Automata

Abstract The processing of logical information has been based, since the time of the first electromechanical computers, on the paradigm of a three‐terminal device operating as a controlled switch, be it a relay, a vacuum tube, or a transistor. Therefore, although the technology has undergone extraordinary developments in terms of device miniaturization, switching speed, reliability, and power consumption, the basic concept behind circuit design has remained substantially unchanged. A bold departure from this traditional implementation is represented by the quantum cellular automaton (QCA) concept, whereby logic computation is achieved by means of two‐dimensional arrays of bistable cells. In this chapter the advantages and scalability of the QCA approach are discussed, as well as the technological difficulties that so far have impaired any attempt to make this technology suitable for large‐scale production.