Spin-based quantum information processing with semiconductor quantum dots and cavity QED

A quantum information processing scheme is proposed with semiconductor quantum dots located in a high-Q single mode QED cavity. The spin degrees of freedom of one excess conduction electron of the quantum dots are employed as qubits. Excitonic states, which can be produced ultrafastly with optical operation, are used as auxiliary states in the realization of quantum gates. We show how properly tailored ultrafast laser pulses and Pauli-blocking effects, can be used to achieve a universal encoded quantum computing.Comment: RevTex, 2 figure

Entanglement in the One-dimensional Kondo Necklace Model

We discuss the thermal and magnetic entanglement in the one-dimensional Kondo necklace model. Firstly, we show how the entanglement naturally present at zero temperature is distributed among pairs of spins according to the strength of the two couplings of the chain, namely, the Kondo exchange interaction and the hopping energy. The effect of the temperature and the presence of an external magnetic field is then investigated, being discussed the adjustment of these variables in order to control the entanglement available in the system. In particular, it is indicated the existence of a critical magnetic field above which the entanglement undergoes a sharp variation, leading the ground state to a completely unentangled phase.Comment: 8 pages, 13 EPS figures. v2: four references adde

On Reduction of Critical Velocity in a Model of Superfluid Bose-gas with Boundary Interactions

The existence of superfluidity in a 3D Bose-gas can depend on boundary interactions with channel walls. We study a simple model where the dilute moving Bose-gas interacts with the walls via hard-core repulsion. Special boundary excitations are introduced, and their excitation spectrum is calculated within a semiclassical approximation. It turns out that the state of the moving Bose-gas is unstable with respect to the creation of these boundary excitations in the system gas + walls, i.e. the critical velocity vanishes in the semiclassical (Bogoliubov) approximation. We discuss how a condensate wave function, the boundary excitation spectrum and, hence, the value of the critical velocity can change in more realistic models, in which ``smooth'' attractive interaction between the gas and walls is taken into account. Such a surface mode could exist in ``soft matter'' containers with flexible walls.Comment: 9 pages (RevTeX), two figures (.ps) incorporated by epsf. submitted to Phys. Lett.

Charge controlled self-assembled quantum dots coupled to photonic crystal nanocavities

The system of charge controlled self-assembled quantum dots coupled to high-Q photonic crystal cavity modes is studied. The quantum dots are embedded in a p-i-n diode structure. Different designs of photonic crystal cavities are used, namely H1 and L3 and the Purcell effect is demonstrated. Furthermore, the fine tuning of the H1 cavity design is studied in order to achieve far field emission profiles that result in higher collection efficiency. An increase in the overall signal from the quantum dot when it is coupled to a cavity is observed, due to the Purcell effect and the improved collection efficiency. This together with the deterministic charging of the quantum dot that is demonstrated, can be used for a single electron spin measurement

Fast quantum computing with semiconductor quantum dots in a microcavity

The paper has been withdrawn by the authorsComment: withdraw