Symmetry-protected Topological Phases at Finite Temperature

We have applied the recently developed theory of topological Uhlmann numbers to a representative model of a topological insulator in two dimensions, the Qi-Wu-Zhang model. We have found a stable symmetry-protected topological (SPT) phase under external thermal fluctuations in two-dimensions. A complete phase diagram for this model is computed as a function of temperature and coupling constants in the original Hamiltonian. It shows the appearance of large stable phases of matter with topological properties compatible with thermal fluctuations or external noise and the existence of critical lines separating abruptly trivial phases from topological phases. These novel critical temperatures represent thermal topological phase transitions. The initial part of the paper comprises a self-contained explanation of the Uhlmann geometric phase needed to understand the topological properties that it may acquire when applied to topological insulators and superconductors.Comment: Contribution to the focus issue on "Artificial Graphene". Edited by Maciej Lewenstein, Vittorio Pellegrini, Marco Polini and Mordechai (Moti) Sege

Observation of topological Uhlmann phases with superconducting qubits

Topological insulators and superconductors at finite temperature can be characterized by the topological Uhlmann phase. However, a direct experimental measurement of this invariant has remained elusive in condensed matter systems. Here, we report a measurement of the topological Uhlmann phase for a topological insulator simulated by a system of entangled qubits in the IBM Quantum Experience platform. By making use of ancilla states, otherwise unobservable phases carrying topological information about the system become accessible, enabling the experimental determination of a complete phase diagram including environmental effects. We employ a state-independent measurement protocol which does not involve prior knowledge of the system state. The proposed measurement scheme is extensible to interacting particles and topological models with a large number of bands.Comment: RevTex4 file, color figure

Precision quantum metrology and nonclassicality in linear and nonlinear detection schemes

We examine whether metrological resolution beyond coherent states is a nonclassical effect. We show that this is true for linear detection schemes but false for nonlinear schemes, and propose a very simple experimental setup to test it. We find a nonclassicality criterion derived from quantum Fisher information.Comment: 4 pages, 1 figur

Cooperation and optimism in a social dilemma

We examine the influence of optimism about local and foreign people on social cooperation using a public goods game. Firstly, we find that optimism fuels social cooperation, and secondly, that this positive effect holds when optimism is focused either jointly or individually

Pinturas a base de polvo de cinc con vehículo inorgánico (Silicatos)

Se prepararon primers pigmentados con 94 de cinc en polvo. Los vehículos utilizados fueron formulados con silicatos de sodio o de potasio, o con una mezcla de ambos, y con diferentes relaciones sílice/álcali, Se determinaron las características de aplicación y de conservación de los primers y se estudió su comportamiento como fondo anticorrosivo en sistemas para uso marino. En línea de flotación, se comportan satisfactoriamente los primers preparados con vehículo a base de silicatos de potasio, y el comportamiento mejora a medida que aumenta la relación sílice/ álcali. Los primers de 24 horas de edad, presentan mayor poder anticorrosivo que aquellos que se aplican inmediatamente de preparados. En sistemas de carena sólo se comportan correctamente los primers de silicato de potasio aplicados luego de 24 horas de su preparación.Zinc rich primers pigmented with 94 zinc dust were prepared. Their vehicles were formulated with sodium and potassium silicates, a mixture of these silicates, and different silica/alkali relations. Brushability, appearence of the film and stability of the primers were evaluated, as well as their anticorrosive properties in marine paint systems. The primers prepared with a vehicle containing potassium silicate gave good results for water line systems and this improvement is proportionally increased by the use of high silica/alkali relations. Moreover the 24 hours old primers have showed better anticorrosive properties than those applied immediatly after prepared. For underwater protection, the best results were only given bypotassium silicate primers applied 24 hours after their production