[en] A novel quantum analogue of the classical problem of cohomology incorporating locality is introduced and is shown to generate those superselection sectors whose charge can be strictly localized. In a 2-dimensional space-time there are further possibilities; in particular, soliton sectors can be generated by this procedure

No abstract available

[en] Problems like those of Schroedinger's can comprise quantum systems as classical systems, the measurement process and reality. After a reviewing the history of interpretation of quantum mechanics it is shown how a generalized algebraic quantum theory (e.g. G.G. Emch 1986) can tackle these problems and paradoxes. This theory treats systems with infinite degrees of freedom and open systems. It is applicable both to quantum as to classical systems and thus to the measurement process with its irreversibility. The usual linear Schroedinger equation is replaced by a non-linear one where the nonlinear terms reflect the interaction of the system with its environment or with the measuring apparatus. (Quittner) To appear also in 'Naturwissenschaft und Weltbild', 1992

[en] Superselection rules (SSRs) constrain the allowed states and operations in quantum theory. They limit preparations and measurements and hence impact our ability to observe non-locality, in particular the violation of Bell inequalities. We show that a reference frame compatible with a particle number SSR does not allow observers to violate a Bell inequality if and only if it is prepared using only local operations and classical communication. In particular, jointly prepared separable reference frames are sufficient for obtaining violations of a Bell inequality. We study the size and non-local properties of such reference frames using superselection-induced variance. These results suggest the need for experimental Bell tests in the presence of superselection.

[en] We investigate decoherence in the limit where the interaction with the environment is weak and the evolution is dominated by the self-Hamiltonian of the system. We show that in this case quantized eigenstates of energy emerge as pointer states selected through the predictability sieve. copyright 1999 The American Physical Society

No abstract available

[en] The normal forms of different one- and two-parametric solutions of Thirring model are connected with each other by making use of generalized conformal shift transformations. A new alternative sources of superselection rules are shown.

[en] Full text: The measurement of open quantum systems has been a main topic since the advent of quantum theory. It is a basic ingredient in quantum information processing. Here, the border where the two worlds of classical and quantum mechanics meet is of significant importance due to the problem of measurement. It has been shown by Zurek that in an open system the environment imposes so-called superselection rules leading to environment-induced superselection (einselection). This means that a set of preferred states (pointer states) survive the coupling with the environment. These pointer states are characterized by their robustness and their ability to create offspring. This ability to advertise information about themselves makes it possible for different observers to measure the same information. The natural promotion of certain information in a quantum system is known as quantum Darwinism. The 'fitness' in the Darwinian sense of the selected states is essentially a measure of their classicality. That is in order to measure a quantum system objectively a system has to be designed where the transition between the classical and quantum world is observable. In this respect we show by a combination of experiment and calculation that an array of electron billiards (open quantum dots) is very well suited. We demonstrate that einselection takes place in electron billiards and a set of pointer states arises. We illustrate that beside the 'regular' (single dot) pointer states a new type of einselected states arise when two or more quantum dots are coupled together and to the environment. This new type of states can not be represented by a linear combination of pointer states of the individual dots. Finally, we discuss the propensity of the new type of einselected states to make offspring in order to see if quantum Darwinism is in action in the array of electron billiards.(author)

[en] We study a theory of short range forces in terms of local observable quantities; among the superselection structure determined by the algebra of all local observables, to each additive independent charge we associate local observables having a meaning analogous to the regularized integrals of charge density fields over a finite volume. Among other assumptions, we require that parastatistics are absent from the theories considered. (orig.)

No abstract available