D-brane Instantons as Gauge Instantons in Orientifolds of Chiral Quiver Theories

Systems of D3-branes at orientifold singularities can receive non-perturbative D-brane instanton corrections, inducing field theory operators in the 4d effective theory. In certain non-chiral examples, these systems have been realized as the infrared endpoint of a Seiberg duality cascade, in which the D-brane instanton effects arise from strong gauge theory dynamics. We present the first UV duality cascade completion of chiral D3-brane theories, in which the D-brane instantons arise from gauge theory dynamics. Chiral examples are interesting because the instanton fermion zero mode sector is topologically protected, and therefore lead to more robust setups. As an application of our results, we provide a UV completion of certain D-brane orientifold systems recently claimed to produce conformal field theories with conformal invariance broken only by D-brane instantons.Comment: 50 pages, 32 figures. v2: version published in JHEP with references adde

On Dimer Models and Closed String Theories

We study some aspects of the recently discovered connection between dimer models and D-brane gauge theories. We argue that dimer models are also naturally related to closed string theories on non compact orbifolds of \BC^2 and \BC^3, via their twisted sector R charges, and show that perfect matchings in dimer models correspond to twisted sector states in the closed string theory. We also use this formalism to study the combinatorics of some unstable orbifolds of \BC^2.Comment: 1 + 25 pages, LaTeX, 11 epsf figure

Revival of quantum correlations without system-environment back-action

Revivals of quantum correlations have often been explained in terms of back-action on quantum systems by their quantum environment(s). Here we consider a system of two independently evolving qubits, each locally interacting with a classical random external field. The environments of the qubits are also independent, and there is no back-action on the qubits. Nevertheless, entanglement, quantum discord and classical correlations between the two qubits may revive in this model. We explain the revivals in terms of correlations in a classical-quantum state of the environments and the qubits. Although classical states cannot store entanglement on their own, they can play a role in storing and reviving entanglement. It is important to know how the absence of back-action, or modelling an environment as classical, affects the kind of system time evolutions one is able to describe. We find a class of global time evolutions where back-action is absent and for which there is no loss of generality in modelling the environment as classical. Finally, we show that the revivals can be connected with the increase of a parameter used to quantify non-Markovianity of the single-qubit dynamics.Comment: 8 pages, 4 figures; this version to appear in Phys. Rev.

Torção aguda do cordão espermático: factor de risco para anticorpos anti-espermatozóides?

A torção aguda do cordão espermático é uma urgência urológica dada a isquémia testicular acompanhante, podendo mesmo levar à necrose testicular se não resolvida atempadamente. A correcção cirúrgica passa pela destorção do cordão espermático atingido e orquidopexia bilateral ou, na presença de torção com isquémia testicular irreversível, pela orquidectomia e orquidopexia contralateral. As eventuais sequelas desta entidade clínica independentemente da cirurgia efectuada, passam por alterações quantitativas e/ou qualitativas do espermograma com repercussão ainda mal esclarecidaemtermos de fertilidade masculina. Caracterizámos os valores de testosterona total, espermograma e a presença sérica de anticorpos anti-espermatozóides (AAE) em 9 doentes com torção aguda unilateral do cordão espermático de modo a caracterizar a sua prevalência nesta amostra comparando os resultados com grupo controlo de 15 indivíduos. Todos os doentes obtiveram valores normais de testosterona total sérica. Cinco doentes não apresentaram AAE, representando 55,6% da amostra e quatro doentes apresentaram AAE, representando 44,4% da amostra. O tempo médio entre a cirurgia e a pesquisa de anticorpos foi de 23,75 meses (6-66) para doentes com AAE positivos e 37,2 meses (10-48) para doentes com AAE negativos. O espermograma revelou-se normal em todos os parâmetros avaliados em apenas três doentes (um com AAE e dois semAAE) e anormal em seis doentes (três com AAE e três sem AAE). Os dois doentes com concentrações mais baixas de espermatozóides apresentavam AAE. Os 15 indivíduos do grupo de controlo não apresentaram AAE. O nosso estudo aponta a torção do cordão espermático como factor de risco para a presença de AAE e para alterações do espermograma, independentemente da presença de AAE e da correcção cirúrgica efectuada

Experimental Realization of a One-way Quantum Computer Algorithm Solving Simon's Problem

We report an experimental demonstration of a one-way implementation of a quantum algorithm solving Simon's Problem - a black box period-finding problem which has an exponential gap between the classical and quantum runtime. Using an all-optical setup and modifying the bases of single-qubit measurements on a five-qubit cluster state, key representative functions of the logical two-qubit version's black box can be queried and solved. To the best of our knowledge, this work represents the first experimental realization of the quantum algorithm solving Simon's Problem. The experimental results are in excellent agreement with the theoretical model, demonstrating the successful performance of the algorithm. With a view to scaling up to larger numbers of qubits, we analyze the resource requirements for an n-qubit version. This work helps highlight how one-way quantum computing provides a practical route to experimentally investigating the quantum-classical gap in the query complexity model.Comment: 9 pages, 5 figure

Dynamics of Entanglement and Bell-nonlocality for Two Stochastic Qubits with Dipole-Dipole Interaction

We have studied the analytical dynamics of Bell nonlocality as measured by CHSH inequality and entanglement as measured by concurrence for two noisy qubits that have dipole-dipole interaction. The nonlocal entanglement created by the dipole-dipole interaction is found to be protected from sudden death for certain initial states

Entanglement Dynamics of Two Independent Cavity-Embedded Quantum Dots

We investigate the dynamical behavior of entanglement in a system made by two solid-state emitters, as two quantum dots, embedded in two separated micro-cavities. In these solid-state systems, in addition to the coupling with the cavity mode, the emitter is coupled to a continuum of leaky modes providing additional losses and it is also subject to a phonon-induced pure dephasing mechanism. We model this physical configuration as a multipartite system composed by two independent parts each containing a qubit embedded in a single-mode cavity, exposed to cavity losses, spontaneous emission and pure dephasing. We study the time evolution of entanglement of this multipartite open system finally applying this theoretical framework to the case of currently available solid-state quantum dots in micro-cavities.Comment: 10 pages, 4 figures, to appear in Topical Issue of Physica Scripta on proceedings of CEWQO 201