Generating single-mode behavior in fiber-coupled optical cavities

We propose to turn two resonant distant cavities effectively into one by coupling them via an optical fiber which is coated with two-level atoms [Franson et al., Phys. Rev. A 70, 062302 (2004)]. The purpose of the atoms is to destructively measure the evanescent electric field of the fiber on a time scale which is long compared to the time it takes a photon to travel from one cavity to the other. Moreover, the boundary conditions imposed by the setup should support a small range of standing waves inside the fiber, including one at the frequency of the cavities. In this way, the fiber provides an additional decay channel for one common cavity field mode but not for the other. If the corresponding decay rate is sufficiently large, this mode decouples effectively from the system dynamics. A single non-local resonator mode is created.Comment: 13 pages, 6 figures, final version, accepted for publicatio

Criticality, factorization and long-range correlations in the anisotropic XY-model

We study the long-range quantum correlations in the anisotropic XY-model. By first examining the thermodynamic limit we show that employing the quantum discord as a figure of merit allows one to capture the main features of the model at zero temperature. Further, by considering suitably large site separations we find that these correlations obey a simple scaling behavior for finite temperatures, allowing for efficient estimation of the critical point. We also address ground-state factorization of this model by explicitly considering finite size systems, showing its relation to the energy spectrum and explaining the persistence of the phenomenon at finite temperatures. Finally, we compute the fidelity between finite and infinite systems in order to show that remarkably small system sizes can closely approximate the thermodynamic limit.Comment: 8 pages, 8 figures. Close to published versio

Protecting subspaces by acting on the outside

Many quantum control tasks aim at manipulating the state of a quantum mechanical system within a finite subspace of states. However, couplings to the outside are often inevitable. Here we discuss strategies which keep the system in the controlled subspace by applying strong interactions onto the outside. This is done by drawing analogies to simple toy models and to the quantum Zeno effect. Special attention is paid to the constructive use of dissipation in the protection of subspaces.Comment: 16 pages, 10 figure

Designing industrial strategy for a low carbon transformation

The recent re-emergence of industrial policy as a legitimate pursuit of governments in Europe and the US has the potential to open up a new realm of policy action for climate change mitigation. This would aim to align efforts to secure national industrial opportunities with the development of low carbon industrial systems, so as to generate both socio-economic and environmental benefits. The paper discusses the role of low carbon industrial strategy in seeking to do this, thereby accelerating transitions to a low carbon economy. It sets out the elements of a more systemic low carbon industrial strategy, including providing a mission-oriented and learning-based approach, drawing on and combining insights from neo-Schumpeterian and ecological economics perspectives

Entangling distant quantum dots using classical interference

We show that it is possible to employ reservoir engineering to turn two distant and relatively bad cavities into one good cavity with a tunable spontaneous decay rate. As a result, quantum computing schemes, that would otherwise require the shuttling of atomic qubits in and out of an optical resonator, can now be applied to distant quantum dots. To illustrate this we transform a recent proposal to entangle two qubits via the observation of macroscopic fluorescence signals [Metz et al., Phys. Rev. Lett. 97, 040503 (2006)] to the electron-spin states of two semiconductor quantum dots. Our scheme requires neither the coherent control of qubit-qubit interactions nor the detection of single photons. Moreover, the scheme is relatively robust against spin-bath couplings, parameter fluctuations, and the spontaneous emission of photons.Comment: 5 pages, 5 figures, revised version, new titl

Low carbon infrastructure investment: extending business models for sustainability

Investment in infrastructure is recognized as a key enabler of economic prosperity, but it is also important for addressing social and environmental challenges, including climate change mitigation and addressing fuel poverty. The UK Government Strategy Investing in Britain’s Future argues that significant investment in “resilient, cost effective and sustainable energy supplies” is needed to meet these challenges. However, current methods of assessing the costs and benefits of infrastructure investment, and the subsequent design of business models needed to deliver this investment, often prioritise partial economic gains over social and environmental objectives. This paper extends the business model canvas approach to allow designing business models and evaluation methods that can incorporate social and environmental value streams and propositions as well as economic values in order to facilitate genuinely sustainable infrastructure investment. It demonstrates the usefulness of this extension through two case studies of the development of smart grids for electricity distribution and local heat delivery networks in the UK. Smart grids are essential for maintaining the security and reliability of electricity systems whilst incorporating increasing amounts of low carbon generation in distribution networks. District heat networks can facilitate the efficient supply of low carbon heat. However, both will require significant levels of investment, co-ordination between public, private and regulatory actors, and will deliver a range of economic, social and environmental costs and benefits to these actors. Drawing on empirical interviews with local actors involved in smart grid and heat network developments, and recent work on valuation and business model canvas analysis, the paper challenges the traditional view of a business model as only creating one form of value. Accounting for multiple types of value helps to identify business models that are more likely to achieve the environmental and social goals of infrastructure transformation and opens the door for new actors. Finally, the paper introduces an approach to complex systems modelling of infrastructure investment decisions to take into account the range of actors and the diversity of motivations of these actors

Evaluation of Intestinal Barrier Dysfunction with Serum Iohexol Concentration in Dogs with Acute Hemorrhagic Diarrhea Syndrome

Histopathologic examination of intestinal biopsies from dogs with acute hemorrhagic diarrhea syndrome (AHDS) reveals necrotizing enteritis and epithelial integrity loss. Serum iohexol measurement has been utilized to assess intestinal permeability. Our hypothesis is that dogs with AHDS have increased intestinal permeability, which is associated with the severity of clinical signs. In this prospective case–control study, 53 client-owned dogs (28 AHDS, 25 healthy controls) were evaluated. Clinical severity was assessed using the AHDS index and systemic inflammatory response syndrome (SIRS) criteria. Simultaneously, dogs received oral iohexol, and serum iohexol concentrations (SICs) were measured two hours later. Results indicated significantly higher (p = 0.002) SIC in AHDS dogs (median: 51 µg/mL; min–max: 9–246) than in healthy controls (30 µg/mL; 11–57). There was a significant positive correlation between AHDS index and SIC (rS = 0.4; p = 0.03) and a significant negative between SIC and serum albumin concentrations (Pearson r = −0.55; p = 0.01). Dogs with severe AHDS (mean 106 µg/mL; range: 17–246) demonstrated significantly higher (p = 0.002) SIC than those with mild to moderate disease (29 µg/mL; 9–54). These findings underscore the association between intestinal permeability and clinical severity in dogs with AHDS assessed by iohexol