Deterministic secure direct communication using GHZ states and swapping quantum entanglement

We present a deterministic secure direct communication scheme via entanglement swapping, where a set of ordered maximally entangled three-particle states (GHZ states), initially shared by three spatially separated parties, Alice, Bob and Charlie, functions as a quantum information channel. After ensuring the safety of the quantum channel, Alice and Bob apply a series local operations on their respective particles according to the tripartite stipulation and the secret message they both want to send to Charlie. By three Alice, Bob and Charlie's Bell measurement results, Charlie is able to infer the secret messages directly. The secret messages are faithfully transmitted from Alice and Bob to Charlie via initially shared pairs of GHZ states without revealing any information to a potential eavesdropper. Since there is not a transmission of the qubits carrying the secret message between any two of them in the public channel, it is completely secure for direct secret communication if perfect quantum channel is used.Comment: 9 pages, no figur

Towards a sustainable innovation policy – institutional structures, stakeholder participation and mixes of policy instruments

Environmental policy and innovation policy regimes at national and EC levels require a more strategic principle and process based approach to policy coherence, in order to achieve greater integration. This paper investigates potential public-private institutional structures, forms of stakeholder participation, and development of mixes of policy instruments that could play a role in integrating environmental policy and innovation policy regimes into a sustainable innovation policy regime. These factors form part of guidance for improving policy processes for promoting sustainable innovation, currently being formulated in a research project under the UK ESRC Sustainable Technologies Programme, aiming to reflect the complexity of both innovation and environmental processes and systems. This paper analyses three aspects of this guidance – the role of public-private institutional structures in policy development; forms of stakeholder participation and related consensual policy decision-making designed to include representatives of the innovation constituency; and approaches to the development of a more coherent and integrated mix of policy instruments. It draws on a project case study of EC Directives and other policy measures relating to alternative energy sources in vehicles; assessment of Integrated Product Policy as an attempt to achieve greater policy coherence; analysis of the Transition Management approach (developed by Kemp and Rotmans, and now being applied to innovation in energy policy by the Netherlands’ Ministry of Economic Affairs); and direct experience of involvement in EC policy processes. Finally, potential institutional developments to move to a more adaptive policy making approach are considered. This would facilitate ‘policy learning’, by institutionalising policy review, learning and correction mechanisms, and so facilitate more rapid reaction to the dynamics of innovation. It is argued that such an approach could be beneficial to sustainable innovation policy, the development of more sustainable innovation systems, and also to the integration of environmental policy with other policy areas

Quantifying the behavior of stock correlations under market stress

Understanding correlations in complex systems is crucial in the face of turbulence, such as the ongoing financial crisis. However, in complex systems, such as financial systems, correlations are not constant but instead vary in time. Here we address the question of quantifying state-dependent correlations in stock markets. Reliable estimates of correlations are absolutely necessary to protect a portfolio. We analyze 72 years of daily closing prices of the 30 stocks forming the Dow Jones Industrial Average (DJIA). We find the striking result that the average correlation among these stocks scales linearly with market stress reflected by normalized DJIA index returns on various time scales. Consequently, the diversification effect which should protect a portfolio melts away in times of market losses, just when it would most urgently be needed. Our empirical analysis is consistent with the interesting possibility that one could anticipate diversification breakdowns, guiding the design of protected portfolios

Spacetime in String Theory

We give a brief overview of the nature of spacetime emerging from string theory. This is radically different from the familiar spacetime of Einstein's relativity. At a perturbative level, the spacetime metric appears as ``coupling constants" in a two dimensional quantum field theory. Nonperturbatively (with certain boundary conditions), spacetime is not fundamental but must be reconstructed from a holographic, dual theory.Comment: 20 pages; references adde

Modeling of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves

We provide a systematic test of empirical theories of covalent bonding in solids using an exact procedure to invert ab initio cohesive energy curves. By considering multiple structures of the same material, it is possible for the first time to test competing angular functions, expose inconsistencies in the basic assumption of a cluster expansion, and extract general features of covalent bonding. We test our methods on silicon, and provide the direct evidence that the Tersoff-type bond order formalism correctly describes coordination dependence. For bond-bending forces, we obtain skewed angular functions that favor small angles, unlike existing models. As a proof-of-principle demonstration, we derive a Si interatomic potential which exhibits comparable accuracy to existing models.Comment: 4 pages revtex (twocolumn, psfig), 3 figures. Title and some wording (but no content) changed since original submission on 24 April 199