Quantum information processing in bosonic lattices

We consider a class of models of self-interacting bosons hopping on a lattice. We show that properly tailored space-temporal coherent control of the single-body coupling parameters allows for universal quantum computation in a given sector of the global Fock space. This general strategy for encoded universality in bosonic systems has in principle several candidates for physical implementation.Comment: 4 pages, 2 figs, RevTeX 4; updated to the published versio

Spin-based optical quantum gates via Pauli blocking in semiconductor quantum dots

We present a solid-state implementation of ultrafast conditional quantum gates. Our proposal for a quantum-computing device is based on the spin degrees of freedom of electrons confined in semiconductor quantum dots, thus benefiting from relatively long decoherence times. More specifically, combining Pauli blocking effects with properly tailored ultrafast laser pulses, we are able to obtain sub-picosecond spin-dependent switching of the Coulomb interaction, which is the essence of our conditional phase-gate proposal. This allows us to realize {\it a fast two qubit gate which does not translate into fast decoherence times} and paves the road for an all-optical spin-based quantum computer.Comment: 14 Pages RevTeX, 3 eps figures include

Effects of low doses of dexamethasone on productive traits and meat quality of veal calves

An experimental administration of dexamethasone was carried out on 15 veal calves in order to assess the rôle of low doses of exogenous glucocorticoids on productive traits and meat quality. Three groups, of five veal calves each, were formed : one group received oral dexamethasone (0.4 mg per calf per day for 25 days), another intramuscular (i. m.) dexamethasone (2 mg at days 14 and 21), and the third was the control. Calves were slaughtered at 165 days of age (day 31). Food conversion ratio (FCR), hot dressing percentage (HDP), chilled dressing percentage (CDP) and shrinkage were determined. From all carcasses, samples of m. longissimus thoracis (between the 8th and 10th rib) were taken in order to evaluate the chemical composition and some organoleptic characteristics : meat colour, water-holding capacity and tenderness. The animals treated with oral dexamethasone showed the lowest daily weight gain (P < 0.05) and the poorest FCR (P < 0.05). Hot dressing percentage, cold dressing percentage and shrinkage were not affected by the oral treatment. The i. m. injections of dexamethasone did not influence the overall performance. Muscle chemical composition and pH were not affected by the treatments; the meat of calves treated with oral dexamethasone was significantly lighter (P < 0.05) and tended to be paler, while i. m. treatment induced intermediate characteristics. The shear force of the meat was rather low. Shear force of cooked meat from animals treated with dexamethasone (both oral and i. m.) was significantly lower than the control (P < 0.05). Treatment with dexamethasone i. m. induced a decrease in water-holding capacity; the oral treatment had no effect on this parameter

Semiconductor-based Geometrical Quantum Gates

We propose an implementation scheme for holonomic, i.e., geometrical, quantum information processing based on semiconductor nanostructures. Our quantum hardware consists of coupled semiconductor macroatoms addressed/controlled by ultrafast multicolor laser-pulse sequences. More specifically, logical qubits are encoded in excitonic states with different spin polarizations and manipulated by adiabatic time-control of the laser amplitudes . The two-qubit gate is realized in a geometric fashion by exploiting dipole-dipole coupling between excitons in neighboring quantum dots.Comment: 4 Pages LaTeX, 3 Figures included. To appear in PRB (Rapid Comm.

Coulomb-enhanced dynamic localization and Bell state generation in coupled quantum dots

We investigate the dynamics of two interacting electrons in coupled quantum dots driven by an AC field. We find that the two electrons can be trapped in one of the dots by the AC field, in spite of the strong Coulomb repulsion. In particular, we find that the interaction may enhance the localization effect. We also demonstrate the field excitation procedure to generate the maximally entangled Bell states. The generation time is determined by both analytic and numerical solutions of the time dependent Schrodinger equation.Comment: 12 pages, 5 figure

Size-dependent decoherence of excitonic states in semiconductor microcrystallites

The size-dependent decoherence of the exciton states resulting from the spontaneous emission is investigated in a semiconductor spherical microcrystallite under condition $a_{B}\ll R_{0}\leq\lambda$. In general, the larger size of the microcrystallite corresponds to the shorter coherence time. If the initial state is a superposition of two different excitonic coherent states, the coherence time depends on both the overlap of two excitonic coherent states and the size of the microcrystallite. When the system with fixed size is initially in the even or odd coherent states, the larger average number of the excitons corresponds to the faster decoherence. When the average number of the excitons is given, the bigger size of the microcrystallite corresponds to the faster decoherence. The decoherence of the exciton states for the materials GaAs and CdS is numerically studied by our theoretical analysis.Comment: 4 pages, two figure