Quantum Computation and Spin Electronics

1 In this chapter we explore the connection between mesoscopic physics and quantum computing. After giving a bibliography providing a general introduction to the subject of quantum information processing, we review the various approaches that are being considered for the experimental implementation of quantum computing and quantum communication in atomic physics, quantum optics, nuclear magnetic resonance, supercon-ductivity, and, especially, normal-electron solid state physics. We discuss five criteria for the realization of a quantum computer and consider the implications that these criteria have for quantum computation using the spin states of single-electron quantum dots. Finally, we consider the transport of quantum information via the motion of individual electrons in mesoscopic structures; specific transport and noise measurements in coupled quantum dot geometries for detecting and characterizing electron-state entanglement are analyzed. The story of why quantum computing and quantum communication are theoretically interesting and important has been told in innumerable places before, and we will just point the reader to some of those. The " prehistory " of quantum computing (up to 1994) consists of the tinkerings of a small number of visionaries on the question of how data could be processed if bits could be put into quantum superpositions of states. The idea of a quantum