Local Realistic Theory for PDC Experiments Based on the Wigner Formalism

In this article we present a local hidden variables model for all experiments involving photon pairs produced in parametric down conversion, based on the Wigner representation of the radiation field. A modification of the standard quantum theory of detection is made in order to give a local realist explanation of the counting rates in photodetectors. This model involves the existence of a real zeropoint field, such that the vacumm level of radiation lies below the threshold of the detectors.Comment: 7 pages, no figure

Free-Space Quantum Key Distribution

Based on the firm laws of physics rather than unproven foundations of mathematical complexity, quantum cryptography provides a radically different solution for encryption and promises unconditional security. Quantum cryptography systems are typically built between two nodes connected to each other through fiber optic. This chapter focuses on quantum cryptography systems operating over free-space optical channels as a cost-effective and license-free alternative to fiber optic counterparts. It provides an overview of the different parts of an experimental free-space quantum communication link developed in the Spanish National Research Council (Madrid, Spain).Comment: 22 pages, 15 figure

From Stochastic Optics to the Wigner Formalism: The Role of the Vacuum Field in Optical Quantum Communication Experiments

The Wigner formalism in the Heisenberg picture constitutes a bridge that connects Quantum Optics to Stochastic Optics. The vacuum field appears explicitly in the formalism, and the wavelike aspects of light are emphasised. In addition, the zeropoint intensity as a threshold for detection is a common denominator in both theories. In this paper, after summarising the basic rules of the Wigner approach and its application to parametric down-conversion, some new results are presented that delve into the physical meaning of the zeropoint field in optical quantum communication. Specifically, the relationship between Bell-state distinguishability and the number of sets of zeropoint modes that take part in the experiment is analysed in terms of the coupling between the phases of the different fields involved and the subtraction of the zeropoint intensity at the detectors. Additionally, the connection between the compatibility theorem in quantum cryptography and zeropoint field is stressed

Exploring the neural correlates of e-Assurance and multi-faced risk in e-Commerce

El comercio electrónico ha permitido a multitud de pequeñas empresas exponer sus productos y aumentar su público objetivo potencial. Pese a la relativa facilidad de introducirse en este mercado, la mayor dificultad estriba en eliminar las barreras que limitan a los consumidores comprar online. Una de las vías que poseen mayor potencial para aumentar la confianza online y reducir el riesgo percibido es dotar a su web de señales de confianza, entre las que destacan los certificados externos, ratings de consumidores y políticas de privacidad. Este estudio precisamente usa una técnica neurocientífica (resonancia magnética funcional) junto a cuestionarios con el propósito de esclarecer objetivamente el procesamiento neurológico de esas tres señales de seguridad online. Además, usando estas nuevas herramientas, pretende dilucidar la debatida dimensionalidad del riesgo percibido. Los resultados aconsejarán a comercios online la señal más útil a incluir en sus webs y se concretarán las dimensiones del riesgo percibido.E-commerce has allowed many small firms sell their products and broaden their target. Despite the relative ease in which vendors enter this marketplace, the strongest difficulty is to decrease barriers which discourage online purchases. One of the most useful ways to increase consumer online trust and reduce perceived risk is creating trust mechanisms in web sites, such as seals of approval, consumer ratings and privacy policies. Specifically, this study applies a neuroscientific tool (functional magnetic resonance imaging- fMRI-) together with questionnaires with the aim to clear up the neural processing of those trust signals (e-assurances). Furthermore, using fMRI, we explore the “under-debated” dimensionality of perceived risk. The findings will advise online retailers with the most useful e-assurance to include in their websites as well as will specify the dimensions of perceived risk