Generalized quantum measurement

We overcome one of Bell's objections to `quantum measurement' by generalizing the definition to include systems outside the laboratory. According to this definition a {\sl generalized quantum measurement} takes place when the value of a classical variable is influenced significantly by an earlier state of a quantum system. A generalized quantum measurement can then take place in equilibrium systems, provided the classical motion is chaotic. This paper deals with this classical aspect of quantum measurement, assuming that the Heisenberg cut between the quantum dynamics and the classical dynamics is made at a very small scale. For simplicity, a gas with collisions is modelled by an `Arnold gas'.Comment: 11 pages, LaTeX, no figures, title change

Quantum state diffusion, measurement and second quantization

Realistic dynamical theories of measurement based on the diffusion of quantum states are nonunitary, whereas quantum field theory and its generalizations are unitary. This problem in the quantum field theory of quantum state diffusion (QSD) appears already in the Lagrangian formulation of QSD as a classical equation of motion, where Liouville's theorem does not apply to the usual field theory formulation. This problem is resolved here by doubling the number of freedoms used to represent a quantum field. The space of quantum fields is then a classical configuration space, for which volume need not be conserved, instead of the usual phase space, to which Liouville's theorem applies. The creation operator for the quantized field satisfies the QSD equations, but the annihilation operator does not satisfy the conjugate eqation. It appears only in a formal role.Comment: 10 page

Quantum transfer functions, weak nonlocality and relativity

The method of transfer functions is developed as a tool for studying Bell inequalities, alternative quantum theories and the associated physical properties of quantum systems. Non-negative probabilities for transfer functions result in Bell-type inequalities. The method is used to show that all realistic Lorentz-invariant quantum theories, which give unique results and have no preferred frame, can be ruled out on the grounds that they lead to weak backward causality.Comment: Plain TeX, 12 pages, no figures. To be submitted Physics Letters A Derivation of Bell inequality corrected (14c) + minor change

Why do Bell experiments?

Experiments over three decades have been unable to demonstrate weak nonlocality in the sense of Bell unambiguously, without loopholes. The last important loophole remaining is the detection loophole, which is being tackled by at least three experimental groups. This letter counters five common beliefs about Bell experiments, and presents alternative scenarios for future developments.Comment: 10 pages, 1 figure, to be submitted to Natur

A general computer program for the Bell detection loophole

The difference between ideal experiments to test Bell's weak nonlocality and the real experiments leads to loopholes. Ideal experiments involve either inequalities (Bell) or equalities (Greenberger, Horne, Zeilinger). Every real experiment has its own critical inequalities, which are almost all more complicated than the corresponding ideal inequalities and equalities. If one of these critical inequalities is violated, then the detection loophole is closed, with no further assumptions. If all the critical inequalities are satisfied, then it remains open, unless further assumptions are made. The computer program described here and published on the website http://www.strings.ph.qmw.ac.uk/QI/main.htm obtains the critical inequalities for any real experiment, given the number of allowed settings of the angles and the corresponding possible output signals for a single run. Given all the necessary conditional probabilities or rates, it tests whether all these inequalities are satisfied.Comment: 10 pages, no figures. Revised version with additional reference to Pitowski and Svozi

Quantum chaos in open systems: a quantum state diffusion analysis

Except for the universe, all quantum systems are open, and according to quantum state diffusion theory, many systems localize to wave packets in the neighborhood of phase space points. This is due to decoherence from the interaction with the environment, and makes the quasiclassical limit of such systems both more realistic and simpler in many respects than the more familiar quasiclassical limit for closed systems. A linearized version of this theory leads to the correct classical dynamics in the macroscopic limit, even for nonlinear and chaotic systems. We apply the theory to the forced, damped Duffing oscillator, comparing the numerical results of the full and linearized equations, and argue that this can be used to make explicit calculations in the decoherent histories formalism of quantum mechanics.Comment: 18 pages standard LaTeX + 9 figures; extensively trimmed; to appear in J. Phys.

Real world evaluation of three models of NHS smoking cessation service in England

<p>Abstract</p> <p>Background</p> <p>NHS Stop Smoking Services provide various options for support and counselling. Most services have evolved to suit local needs without any retrospective evaluation of their efficiency.</p> <p>Three local service evaluations were carried out at Bournemouth & Poole Teaching Primary Care Trust (PCT) (PCT1), NHS South East Essex (PCT2) and NHS Warwickshire (PCT3) to describe the structure and outcomes associated with different services.</p> <p>Result</p> <p>Standardised interviews with key personnel in addition to analysis of data from 400 clients accessing the service after 1^stApril 2008 in each PCT. The PCTs varied in geography, population size and quit rate (47%-63%). Services were delivered by PCT-led specialist teams (PCT1), community-based healthcare providers (PCT3) and a combination of the two (PCT2) with varying resources and interventions in each.</p> <p>Group support resulted in the highest quit rates (64.3% for closed groups v 42.6% for one-to-one support (PCT1)). Quit rates were higher for PCT (75.0%) v GP (62.0%) and pharmacist-delivered care (41.0%) where all existed in the same model (PCT2). The most-prescribed therapy was NRT (55.8%-65.0%), followed by varenicline (24.5%-34.3%), counselling alone (6.0%-7.8%) and bupropion (2.0%-4.0%).</p> <p>Conclusion</p> <p>The results suggest that service structure, method of support, healthcare professional involved and pharmacotherapy all play a role in a successful quit. Services must be tailored to support individual needs with patient choice and access to varied services being key factors.</p