40,678 research outputs found
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Lightweight Vacuum Jacket for Cryogenic Insulation - Appendices to Final Report
The feasibility is demonstrated of producing a lightweight vacuum jacket using state-of-the-art technology and materials. Design and analytical studies were made on an orbital maneuvering system fuel tank. Preliminary design details were completed for the tank assembly which included an optimized vacuum jacket and multilayered insulation system. A half-scale LH2 test model was designed and fabricated and a force/stiffness proof test was conducted on the vacuum jacket. A vacuum leak rate of 0.00001 was measured, approximately 1500 hours of vacuum pressure was sustained, and 29 vacuum pressure cycles were experienced prior to failure. For vol. 1, see N75-26192
Quaternions, octonions and Bell-type inequalities
Multipartite Bell-type inequalities are derived for general systems. They
involve up to eight observables with arbitrary spectra on each site. These
inequalities are closely related to the algebras of quaternions and octonions.Comment: 4 pages, no figure
Social work in movement: marketisation, differentiation and managerial performativity in Sweden and England
This article considers the changing nature of social work in England and Sweden in the context of neoliberal reforms, and the consequences of the ongoing shifts to marketisation and differentiation, managerialism and performativity. Drawing on secondary sources and some interview data from English and Swedish social workers, the article argues that social workers in England and Sweden face similar shifts as marketisation, differentiation, managerialism and its related performativity reshape the occupation, all related to the influence of the macro-context of neoliberalism. ‘Evidence based practice’ has become elevated as an important approach in line with increasing managerialism and performativity, affecting micro processes of everyday working life. Differences between the two countries lie largely in the timing of reforms and how social workers respond to them in organised ways – through mobilisation within the profession in England and through trades unions and local authorities in Sweden. The changes create uncertainty for social workers; while they are not merely passive victims of change they face difficult conditions in which to forge alternative models of professional practice. Contrary to what might have been expected, given the different social, political and historical legacies in Sweden and England of social democracy and liberalism respectively, comparing the social work occupation in these two countries finds many more similarities than differences in how marketisation, differentiation, managerialism and performativity impact on the occupation
Quantum Equilibrium and the Origin of Absolute Uncertainty
The quantum formalism is a ``measurement'' formalism--a phenomenological
formalism describing certain macroscopic regularities. We argue that it can be
regarded, and best be understood, as arising from Bohmian mechanics, which is
what emerges from Schr\"odinger's equation for a system of particles when we
merely insist that ``particles'' means particles. While distinctly
non-Newtonian, Bohmian mechanics is a fully deterministic theory of particles
in motion, a motion choreographed by the wave function. We find that a Bohmian
universe, though deterministic, evolves in such a manner that an {\it
appearance} of randomness emerges, precisely as described by the quantum
formalism and given, for example, by ``\rho=|\psis|^2.'' A crucial ingredient
in our analysis of the origin of this randomness is the notion of the effective
wave function of a subsystem, a notion of interest in its own right and of
relevance to any discussion of quantum theory. When the quantum formalism is
regarded as arising in this way, the paradoxes and perplexities so often
associated with (nonrelativistic) quantum theory simply evaporate.Comment: 75 pages. This paper was published a long time ago, but was never
archived. We do so now because it is basic for our recent article
quant-ph/0308038, which can in fact be regarded as an appendix of the earlier
on
Inductive Entanglement Classification of Four Qubits under SLOCC
Using an inductive approach to classify multipartite entangled states under
stochastic local operations and classical communication introduced recently by
the authors [Phys. Rev. A 74, 052336 (2006)], we give the complete
classification of four-qubit entangled pure states. Apart from the expected
degenerate classes, we show that there exist eight inequivalent ways to
entangle four qubits. In this respect, permutation symmetry is taken into
account and states with a structure differing only by parameters inside a
continuous set are considered to belong to the same class.Comment: 11 pages and no figures. Accepted in PR
Constructing quantum games from non-factorizable joint probabilities
A probabilistic framework is developed that gives a unifying perspective on
both the classical and the quantum games. We suggest exploiting peculiar
probabilities involved in Einstein-Podolsky-Rosen (EPR) experiments to
construct quantum games. In our framework a game attains classical
interpretation when joint probabilities are factorizable and a quantum game
corresponds when these probabilities cannot be factorized. We analyze how
non-factorizability changes Nash equilibria in two-player games while
considering the games of Prisoner's Dilemma, Stag Hunt, and Chicken. In this
framework we find that for the game of Prisoner's Dilemma even non-factorizable
EPR joint probabilities cannot be helpful to escape from the classical outcome
of the game. For a particular version of the Chicken game, however, we find
that the two non-factorizable sets of joint probabilities, that maximally
violates the Clauser-Holt-Shimony-Horne (CHSH) sum of correlations, indeed
result in new Nash equilibria.Comment: Revised in light of referee's comments, submitted to Physical Review
Hardy's argument and successive spin-s measurements
We consider a hidden-variable theoretic description of successive
measurements of non commuting spin observables on a input spin-s state. In this
scenario, the hidden-variable theory leads to a Hardy-type argument that
quantum predictions violate it. We show that the maximum probability of success
of Hardy's argument in quantum theory is , which is more
than in the spatial case.Comment: 7 page
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