Bell's inequality and the coincidence-time loophole

This paper analyzes effects of time-dependence in the Bell inequality. A generalized inequality is derived for the case when coincidence and non-coincidence [and hence whether or not a pair contributes to the actual data] is controlled by timing that depends on the detector settings. Needless to say, this inequality is violated by quantum mechanics and could be violated by experimental data provided that the loss of measurement pairs through failure of coincidence is small enough, but the quantitative bound is more restrictive in this case than in the previously analyzed "efficiency loophole."Comment: revtex4, 3 figures, v2: epl document class, reformatted w slight change

Commercial integration of storage and responsive demand to facilitate wind energy on the Shetland Islands

The Northern Isles New Energy Solutions (NINES) project seeks to implement Active Network Management (ANM) on the Shetland Islands in a manner which reduces customers’ energy consumption, lowers peak demand and facilitates an increase in the proportion of electricity from wind, in order to take advantage of the unique wind resource of the islands. This presentation focuses on the commercial frameworks and trading arrangements necessary to permit additional wind capacity onto the islanded network through the active use of storage and responsive demand technologies. The network is modelled using a Dynamic Optimal Power Flow (DOPF) framework, which allows the unit scheduling of different combinations of generation, storage and demand to be optimised according to different optimisation goals. This is used as a foundation to explore the value of wind energy and storage in meeting the long-term goals of the network, the forms of trading and markets which may be used to contract services, and the potential for responsive demand to facilitate different forms of connection agreements and curtailment strategies for new wind farms. In modelling the Shetland network using Dynamic Optimal Power Flow (DOPF), the optimum unit commitment schedule is determined across a daily horizon for different network topologies, including variable levels of wind generation, storage and demand-side response - primarily storage heaters and water tanks controllable by the Distribution System Operator via Active Network Management. This informs the level of wind generation which may be accepted onto the network, and allows the creation and testing of commercial agreements both for wind generators keen to utilise the unique resource of the islands, as well as allowing third-party operation of storage, and reducing the peak energy demand of domestic consumers. This allows a greater level of demand to be supplied by non-thermal sources through the time-shifting of demand against the availability of the wind resource. Support of the grid through reserve and response is considered in the context of maintaining system stability, with the aim of procuring services through third-party contractual arrangements. Data collected from the operational history of the islands and technology trials demonstrate the feasibility of these approaches and their potential applicability to other constrained distribution networks with the potential for high levels of wind generation. The data from trials of domestic storage equipment and modelling of wind curtailment demonstrate quantitatively the ways in which commercial integration of modern storage and responsive demand can be used to increase the utilisation of wind energy on islanded networks, which may often have increased renewable resources but limited grid capacity. It is shown that there are a number of trading and connection agreements which can be used to contract for generation and ancillary services to meet these goals

Experimenter's Freedom in Bell's Theorem and Quantum Cryptography

Bell's theorem states that no local realistic explanation of quantum mechanical predictions is possible, in which the experimenter has a freedom to choose between different measurement settings. Within a local realistic picture the violation of Bell's inequalities can only be understood if this freedom is denied. We determine the minimal degree to which the experimenter's freedom has to be abandoned, if one wants to keep such a picture and be in agreement with the experiment. Furthermore, the freedom in choosing experimental arrangements may be considered as a resource, since its lacking can be used by an eavesdropper to harm the security of quantum communication. We analyze the security of quantum key distribution as a function of the (partial) knowledge the eavesdropper has about the future choices of measurement settings which are made by the authorized parties (e.g. on the basis of some quasi-random generator). We show that the equivalence between the violation of Bell's inequality and the efficient extraction of a secure key - which exists for the case of complete freedom (no setting knowledge) - is lost unless one adapts the bound of the inequality according to this lack of freedom.Comment: 7 pages, 2 figures, incorporated referee comment

Causal Quantum Theory and the Collapse Locality Loophole

Causal quantum theory is an umbrella term for ordinary quantum theory modified by two hypotheses: state vector reduction is a well-defined process, and strict local causality applies. The first of these holds in some versions of Copenhagen quantum theory and need not necessarily imply practically testable deviations from ordinary quantum theory. The second implies that measurement events which are spacelike separated have no non-local correlations. To test this prediction, which sharply differs from standard quantum theory, requires a precise theory of state vector reduction. Formally speaking, any precise version of causal quantum theory defines a local hidden variable theory. However, causal quantum theory is most naturally seen as a variant of standard quantum theory. For that reason it seems a more serious rival to standard quantum theory than local hidden variable models relying on the locality or detector efficiency loopholes. Some plausible versions of causal quantum theory are not refuted by any Bell experiments to date, nor is it obvious that they are inconsistent with other experiments. They evade refutation via a neglected loophole in Bell experiments -- the {\it collapse locality loophole} -- which exists because of the possible time lag between a particle entering a measuring device and a collapse taking place. Fairly definitive tests of causal versus standard quantum theory could be made by observing entangled particles separated by $\approx 0.1$ light seconds.Comment: Discussion expanded; typos corrected; references adde

The Scottish electricity dispatch model

This paper presents the Scottish Electricity Dispatch Model (SEDM), a cost minimization power system optimization model designed as a tool to investigate potential development trajectories of the Great Britain (GB) power system with particular focus on the Scottish region. Results of SEDM studies investigating the impact of low carbon policies on carbon emissions, generation portfolios and system costs are described. Two potential policies are investigated: carbon pricing and emissions limits, compared to a base scenario with neither of these policies included, but featuring financial support for low carbon generation in line with current GB policy. Model results suggest that carbon emissions could be reduced by up to 95.6% by 2050 with strict emissions limits, achieved largely through an eighteen fold increase in renewable generation capacity. This results in an increase in system costs (including carbon pricing costs) of up to 23.4% compared to the base case, in which carbon emissions increase by 130.8% from present day to 2050. This suggests current policies will be insufficient to achieve a reduction in carbon emissions to the level suggested by the UK’s Committee on Climate Change (CCC)

Modelling the potential impacts of locational versus system-wide strike prices in contracts for difference for low carbon generation

This paper describes the use of a cost - minimisation algorithm to explore the potential impact of two options for financial support for low carbon generation in the form of contracts for difference in a system with locational marginal pricing: 1. with a system-wide strike price; 2. with locational strike prices. A two zone system is modelled with the additional financial support for low carbon generation represented as negative variable costs that have the effect of filling in the difference between wholesale market prices and the strike price, the latter intended to cover the long-run costs of low carbon generation. The British case is modelled in which there is a limit to the total top-up expenditure. It is shown that the case of a system-wide strike price can result in less new low carbon generation capacity compared with the case of locational strike prices, due to the increased top-up spend in the lower price zone more rapidly meeting the constraint on the total cost of top-up payments to low carbon generation. However, it is also shown that the imposition of this constraint leads to a failure of the model to settle on one solution due to the non-convex relationship between installed capacity of low carbon generation and wholesale market price

Managing regional security of supply : a case study from Scotland

Securing the supply of electricity to a region of a power system requires either generation capacity within that region, or transmission import capability coupled with generation elsewhere in the power system. The problem is one of co-optimising generation and transmission infrastructure. This paper begins by discussing changes in Great Britain (GB) regulator environment affecting the provision of regional security of supply: changes to the transmission charging regime; new regulatory arrangements including enhancements to the System Operator’s role, and the opening up of major new transmission projects to competition; and some limitations of the existing standard defining the methodology for calculating secure transmission capabilities. Scotland, as a region of the GB power system, provides an interesting case study in which to investigate the allocation of contributions to regional security of supply between transmission and various categories of generation. In particular, intermittent generation is currently ignored when calculating the level of transmission import capability required to maintain security of supply in a region, whilst it is considered in overall generation adequacy calculations at a system level. Whilst wind generation is not dispatchable, it is shown here that it does provide an additional source of generation availability that should be considered in studies into transmission import requirements. This paper uses historical data for Scottish generation availability from recent winters to investigate the likely impact of changes to the Scottish generation fleet on the need for secure transmission import capability into Scotland. It calculates transmission requirements based on the risk of requiring demand reduction within a region. Scenarios representing possible generation backgrounds in Scotland over the coming decade show that, measured in this way, wind generation can offset transmission import requirements by up to 25% of its installed capacity. The key conclusions of the paper are that a risk-based analysis of regional security of supply and transmission requirements can help allocate the true impact of different generators on the transmission import capability needed to secure supply to a region. Such a method can therefore be useful in informing the allocation of charges between parties and in developing planning standards to shape future investment in the system

Optimal Bell tests do not require maximally entangled states

Any Bell test consists of a sequence of measurements on a quantum state in space-like separated regions. Thus, a state is better than others for a Bell test when, for the optimal measurements and the same number of trials, the probability of existence of a local model for the observed outcomes is smaller. The maximization over states and measurements defines the optimal nonlocality proof. Numerical results show that the required optimal state does not have to be maximally entangled.Comment: 1 figure, REVTEX

Laser cooling of trapped ytterbium ions with an ultraviolet diode laser

We demonstrate an ultraviolet diode laser system for cooling of trapped ytterbium ions. The laser power and linewidth are comparable to previous systems based on resonant frequency doubling, but the system is simpler, more robust, and less expensive. We use the laser system to cool small numbers of ytterbium ions confined in a linear Paul trap. From the observed spectra, we deduce final temperatures < 270 mK.Comment: submitted to Opt. Let

A review of probabilistic methods for defining reserve requirements

In this paper we examine potential improvements in how load and generation forecast uncertainty is captured when setting reserve levels in power systems with significant renewable generation penetration and discuss the merit of proposed new methods in this area. One important difference between methods is whether reserves are defined based on the marginal distribution of forecast errors, as calculated from historic data, or whether the conditional distribution, specific to the time at which reserves are being scheduled, is used. This paper is a review of published current practice in markets which are at the leading edge of this problem, summarizing their experiences, and aligning it with academic modeling work. We conclude that the ultimate goal for all markets expected to manage high levels of renewable generation should be a reserve setting mechanism which utilizes the best understanding of meteorological uncertainties combined with traditional models of uncertainty arising from forced outages