Quantum simulation of a topological Mott insulator with Rydberg atoms in a Lieb lattice

We propose a realistic scheme to quantum simulate the so-far experimentally unobserved topological Mott insulator phase-an interaction-driven topological insulator-using cold atoms in an optical Lieb lattice. To this end, we study a system of spinless fermions in a Lieb lattice, exhibiting repulsive nearest-and next-to-nearest-neighbor interactions and derive the associated zero-temperature phase diagram within mean-field approximation. In particular, we analyze how the interactions can dynamically generate a charge density wave ordered, a nematic, and a topologically nontrivial quantum anomalous Hall phase. We characterize the topology of the different phases by the Chern number and discuss the possibility of phase coexistence. Based on the identified phases, we propose a realistic implementation of this model using cold Rydberg-dressed atoms in an optical lattice. The scheme, which allows one to access, in particular, the topological Mott insulator phase, robustly and independently of its exact position in parameter space, merely requires global, always-on off-resonant laser coupling to Rydberg states and is feasible with state-of-the-art experimental techniques that have already been demonstrated in the laboratory.

Generic helical edge states due to Rashba spin-orbit coupling in a topological insulator

We study the helical edge states of a two-dimensional topological insulator without axial spin symmetry due to the Rashba spin-orbit interaction. Lack of axial spin symmetry can lead to so-called generic helical edge states, which have energy-dependent spin orientation. This opens the possibility of inelastic backscattering and thereby nonquantized transport. Here we find analytically the new dispersion relations and the energy dependent spin orientation of the generic helical edge states in the presence of Rashba spin-orbit coupling within the Bernevig-Hughes-Zhang model, for both a single isolated edge and for a finite width ribbon. In the single-edge case, we analytically quantify the energy dependence of the spin orientation, which turns out to be weak for a realistic HgTe quantum well. Nevertheless, finite size effects combined with Rashba spin-orbit coupling result in two avoided crossings in the energy dispersions, where the spin orientation variation of the edge states is very significantly increased for realistic parameters. Finally, our analytical results are found to compare well to a numerical tight-binding regularization of the model.

Gaming learning analytics for serious games

Los juegos serios (o videojuegos educativos), se consideran una herramienta importante para la educación en el futuro. Por ello, se está invirtiendo mucho esfuerzo en el análisis de su corrección e idoneidad para alcanzar los objetivos educativos pretendidos. El campo de análisis de aprendizaje con juegos pretende proporcionar herramientas que verifiquen estas características mejorando la calidad y efectividad de los juegos serios. Para ello, se necesitan normalmente tres etapas: 1), monitorizar los datos de la interacción del jugador con el juego; 2), analizar esos datos recolectados; y 3), visualizar los resultados. En este contexto, hay algunos asuntos importantes a considerar: nivel de conocimiento del juego, receptor de las visualizaciones finales o cantidad y complejidad de los datos. Estas ideas se ponen en práctica con dos ejemplos de juegos serios centrándonos en las dos últimas etapas del proceso. Se realizan varios análisis y visualizaciones con ellos considerando los diferentes aspectos antes mencionados. Entre las conclusiones que se pueden extraer, destaca que, a pesar de haber algunos aspectos aún por mejorar, el análisis de aprendizaje con juegos es una herramienta esencial para muchos usuarios con una amplia variedad de intereses en juego serios.

Error tolerance of topological codes with independent bit-flip and measurement errors

Topological quantum error correction codes are currently among the most promising candidates for efficiently dealing with the decoherence effects inherently present in quantum devices. Numerically, their theoretical error threshold can be calculated by mapping the underlying quantum problem to a related classical statistical-mechanical spin system with quenched disorder. Here, we present results for the general fault-tolerant regime, where we consider both qubit and measurement errors. However, unlike in previous studies, here we vary the strength of the different error sources independently. Our results highlight peculiar differences between toric and color codes. This study complements previous results published in New J. Phys. 13, 083006 (2011).