In order to investigate strong cotunneling we develop a microscopic theory of cotunneling based on the density-operator formalism and using the projection operator technique. The master equation for the QDS and the expressions for current and noise in cotunneling in terms of the stationary state of the QDS are derived and applied to QDS with a nearly degenerate and continuous spectrum. With present-day technology, spins in semiconductor quantum dots can be created, coherently manipulated, and measured. The ability of controlling spins in semiconductor nanostructures has new and exciting applications in electronics and information processing, including quantum computing and quantum communication. We give an overview over some of the theoretical work motivated by the potential use of electron spins in quantum dots as qubits for quantum information processing.
Entanglement acts as a fundamental resource for many known quantum information processing schemes.
We discuss recently proposed schemes to detect entanglement of electrons in normal and superconducting wires via transport and noise measurements. Various physical implementations of quantum computers are being investigated, although the requirements that must be met to make such devices a reality in the laboratory at present involve capabilities well beyond the state of the art. Here we introduced an explicit scheme in which the Heisenberg interaction alone suffices to implement exactly any quantum computer circuit. This capability comes at a price of a factor of three in additional qubits, and about a factor of ten in additional two-qubit operations. Spin interactions and switching in vertically tunnel-coupled quantum dots Guido Burkard, Georg Seelig, and Daniel Loss Phys.