Electron spins in quantum dots for spintronics and quantum computation

Coherent manipulation, filtering, and measurement of electronic spin in quantum dots and other nanostructures have promising applications in conventional and in quantum information processing and transmission. We present an overview of our theoretical proposal to implement a quantum computer using electron spins in quantum dots as qubits. We discuss all necessary requirements towards a scalable quantum computer including one- and two qubit gates and read in/out tasks. We then present some concepts for promising single quantum dot devices which eventually could be used as building blocks for sophisticated spintronic devices. We show how a single quantum dot can act as an efficient spin filter, Further, in combination with an ESR source, a quantum dot can be used as a single spin memory or as a spin pump. In addition, the sequential tunneling current through a quantum dot in the presence of an ESR field can exhibit a resonance whose line width is deter-mined by the decoherence time T-2 of a single dot-spin. Finally, we consider mobile non-local spin entangled electrons as needed for quantum communication. We propose how to create such EPR pairs by means of Andreev tunneling at a superconductor-normal junction and discuss experimental setups in which spin entanglement may be detected via transport measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.