Collective decoherence of cold atoms coupled to a Bose-Einstein condensate

We examine the time evolution of cold atoms (impurities) interacting with an environment consisting of a degenerate bosonic quantum gas. The impurity atoms differ from the environment atoms, being of a different species. This allows one to superimpose two independent trapping potentials, each being effective only on one atomic kind, while transparent to the other. When the environment is homogeneous and the impurities are confined in a potential consisting of a set of double wells, the system can be described in terms of an effective spin-boson model, where the occupation of the left or right well of each site represents the two (pseudo)-spin states. The irreversible dynamics of such system is here studied exactly, i.e. not in terms of a Markovian master equation. The dynamics of one and two impurities is remarkably different in respect of the standard decoherence of the spin-boson system. In particular, we show: (i) the appearance of coherence oscillations, (ii) the presence of super and subdecoherent states that differ from the standard ones of the spin-boson model, and (iii) the persistence of coherence in the system at long times. We show that this behaviour is due to the fact that the pseudospins have an internal spatial structure. We argue that collective decoherence also prompts information about the correlation length of the environment. In a one-dimensional (1D) configuration, one can change even more strongly the qualitative behaviour of the dephasing just by tuning the interaction of the bath.

The Evolution of European Identity: Using biographical methods to study the development of European identity

Based upon the original application to the European Commission, this article gives insights into the thinking of the Euroidentities team at the point that the project began. The question: “Is the European ‘identity project’ failing?” is posed in the sense that the political and economic attainments of the European Union have not been translated into a sense of identity with or commitment to Europe from the populaces that have benefited from them. The urgency of European ‘identity work’ is asserted with a number of levels for the construction of European identity being hypothesized. Euroidentities is intended to break conceptual ground by bringing together on an equal footing two apparently antagonistic views of identity -- the collective and institutional and the individual and biographical – to give a more anchored and nuanced view of identity formation and transformation than either can provide on its own. Rather than following the dominant approaches to research on European identity that have been macro-theoretical and ‘top-down’, retrospective in-depth qualitative biographical interviews are planned since they provide the ideal means of gaining insight into the formation of a European identity or multiple identities from the ‘bottom up’ perspective of non-elite groups. The reliability of analysis will be buttressed by the use of contrastive comparison between cases, culminating in contrastive comparison across the national project teams between cases drawn from different ‘sensitized groups’ that provide the fieldwork structure of the project. The paper concludes with a summary of some of the more significant findings.