Proposals for quantum computers based on spin degrees of freedom require that individual qubits are placed close
enough so to have a significant exchange interaction between them. We have found theoretically that mixed light-matter
states (polaritons) in planar microcavities can give an extremely long range spin coupling. This implies that spin qubits
can be located several hundreds of nanometers apart while still retaining control on pair interaction through the use of
polaritons. This spin control scheme can be scaled to an array of qubits in a quantum dot lattice. We have theoretically
investigated a lattice of identical quantum dots (or impurity states) coupled to two dimensional photon modes in a planar
cavity. This geometry can be used to design polaritons with novel properties, based on the spatial modulation of the
exciton wave function in the plane of the dots. The application of this structure to the realization of spin-qubit quantum
memories will be discussed.
We discuss schemes for the realization of quantum information devices using optical techniques and the electronic and spin degrees of freedom of diluted impurities in semiconductors. State-of-the-art nano-optical techniques can address a single impurity localized in a
semiconductor. The optical properties of the host can be used to
efficiently control the internal degrees of freedom of the impurities,
and therefore to encode and process quantum information.