Quantum computers and quantum coherence

If the states of spins in solids can be created, manipulated, and measured at the single-quantum level an entirely new form of information processing, quantum computing, will be possible. We first give an overview of quantum information processing, showing that the famous Shor speedup of integer fac toring is just one of a host of important applications for qubits, includin g cryptography, counterfeit protection, channel capacity enhancement, distr ibuted computing, and others. We review our proposed spin-quantum dot archi tecture for a quantum computer. and we indicate a variety of first generati on materials, optical, and electrical measurements which should be consider ed. We analyze the efficiency of a two-dot device as a transmitter of quant um information via the propagation of qubit carriers (i.e. electrons) in a Fermi sea. (C) 1999 Elsevier Science B.V. All rights reserved.