Unexpected reemergence of von Neumann theorem

Is is shown here that the "simple test of quantumness for a single system" of arXiv:0704.1962 (for a recent experimental realization see arXiv:0804.1646) has exactly the same relation to the discussion of to the problem of describing the quantum system via a classical probabilistic scheme (that is in terms of hidden variables, or within a realistic theory) as the von Neumann theorem (1932). The latter one was shown by Bell (1966) to stem from an assumption that the hidden variable values for a sum of two non-commuting observables (which is an observable too) have to be, for each individual system, equal to sums of eigenvalues of the two operators. One cannot find a physical justification for such an assumption to hold for non-commeasurable variables. On the positive side. the criterion may be useful in rejecting models which are based on stochastic classical fields. Nevertheless the example used by the Authors has a classical optical realization

Gaming on the edge: using seams in ubicomp games

Outdoor multi-player games are an increasingly popular application area for ubiquitous computing, supporting experimentation both with new technologies and new user experiences. This paper presents an outdoor ubicomp game that exploits the gaps or seams that exist in complex computer systems. Treasure is designed so that players move in and out of areas of wireless network coverage, taking advantage not only of the connectivity within a wireless ‘hotspot’ but of the lack of connectivity outside it. More broadly, this paper discusses how the notion of seamful design can be a source of design ideas for ubicomp games

N-particle nonclassicality without N-particle correlations

Most of known multipartite Bell inequalities involve correlation functions for all subsystems. They are useless for entangled states without such correlations. We give a method of derivation of families of Bell inequalities for N parties, which involve, e.g., only (N-1)-partite correlations, but still are able to detect proper N-partite entanglement. We present an inequality which reveals five-partite entanglement despite only four-partite correlations. Classes of inequalities introduced here can be put into a handy form of a single non-linear inequality. An example is given of an N qubit state, which strongly violates such an inequality, despite having no N-qubit correlations. This surprising property might be of potential value for quantum information tasks.Comment: 5 page

Digital transformation readiness : perspectives on academia and library outcomes in information literacy

This study examines the readiness of a faculty for the social challenges caused by the digital transformation in academia with the use of covariance-based structural equation modeling (CBSEM). Based on the survey results, we have examined the interplay between factors related to digital transformation. The concepts of information literacy and digital literacy related to academic librarianship were used as the basis for the self-efficacy and empowerment necessary to achieve individual success during digital changes in the academic community. We then checked how such a sense of empowerment among academics explains the presence of information culture in this community and different approaches to information management. The factors of information management and information use were presented as affecting a university's institutional readiness for the new requirements of digital transformation from the perspective of governance issues. The findings highlight that information literacy underlies academics' empowerment and a high level of self-efficacy driven by this literacy can also be indirectly translated into the formation of pro-active information culture that strengthens an academic's position in creating information use outcomes and by making them ready for digital transformation. Through information literacy outcomes the academic libraries can turn out to be an important transformative force in terms of digital changes at universities

Vacuum as a less hostile environment to entanglement

We derive sufficient conditions for infinite-dimensional systems whose entanglement is not completely lost in a finite time during its decoherence by a passive interaction with local vacuum environments. The sufficient conditions allow us to clarify a class of bipartite entangled states which preserve their entanglement or, in other words, are tolerant against decoherence in a vacuum. We also discuss such a class for entangled qubits.Comment: Replaced by the published versio

Guidelines and infrastructure for the design and implementation of highly adaptive, context-aware, mobile, peer-to-peer systems

Through a thorough review of existing literature, and extensive study of two large ubicomp systems, problems are identified with current mobile design practices, infrastructures and a lack of required software. From these problems, a set of guidelines for the design of mobile, peer-to-peer, context-aware systems are derived. Four key items of software infrastructure that are desirable but currently unavailable for mobile systems are identified. Each of these items of software are subsequently implemented, and the thesis describes each one, and at least one system in which each was used and trialled. These four items of mobile software infrastructure are: An 802.11 wireless driver that is capable of automatically switching between ad hoc and infrastructure networks when appropriate, combined with a peer discovery mechanism that can be used to identify peers and the services running and available on them. A hybrid positioning system that combines GPS, 802.11 and GSM positioning techniques to deliver location information that is almost constantly available, and can collect further 802.11 and GSM node samples during normal use of the system. A distributed recommendation system that, in addition to providing standard recommendations, can determine the relevance of data stored on the mobile device. This information is used by the same system to prioritise data when exchanging information with peers and to determine data that may be culled when the system is low on storage space without greatly affecting overall system performance. An infrastructure for creating highly adaptive, context-aware mobile applications. The Domino infrastructure allows software functionality to be recommended, exchanged between peers, installed, and executed, at runtime

Experimental test of nonlocal realistic theories without the rotational symmetry assumption

We analyze the class of nonlocal realistic theories that was originally considered by Leggett [Found. Phys. 33, 1469 (2003)] and tested by us in a recent experiment [Nature (London) 446, 871 (2007)]. We derive an incompatibility theorem that works for finite numbers of polarizer settings and that does not require the previously assumed rotational symmetry of the two-particle correlation functions. The experimentally measured case involves seven different measurement settings. Using polarization-entangled photon pairs, we exclude this broader class of nonlocal realistic models by experimentally violating a new Leggett-type inequality by 80 standard deviations.Comment: Published versio

Rotational invariance as an additional constraint on local realism

Rotational invariance of physical laws is a generally accepted principle. We show that it leads to an additional external constraint on local realistic models of physical phenomena involving measurements of multiparticle spin 1/2 correlations. This new constraint rules out such models even in some situations in which standard Bell inequalities allow for explicit construction of such models. The whole analysis is performed without any additional assumptions on the form of local realistic models.Comment: 4 page

Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality

We address the question as to whether an entangled state that satisfies local realism will give a violation of the same, after entanglement swapping in a suitable scenario. We consider such possibility as a kind of superadditivity in nonclassicality. Importantly, it will indicate that checking for violation of local realism, in the state obtained after entanglement swapping, can be a method for detecting entanglement in the input state of the swapping procedure. We investigate various entanglement swapping schemes, which involve mixed initial states. The strength of violation of local realism by the state obtained after entanglement swapping, is compared with the one for the input states. We obtain a kind of superadditivity of violation of local realism for Werner states, consequent upon entanglement swapping involving Greenberger-Horne-Zeilinger state measurements. We also discuss whether entanglement swapping of specific states may be used in quantum repeaters with a substantially reduced need to perform the entanglement distillation step.Comment: 11 pages, 6 figures, RevTeX4; v2: new discussions added, published versio

Homogenization of Bell inequalities

A technique, which we call homogenization, is applied to transform CH-type Bell inequalities, which contain lower order correlations, into CHSH-type Bell inequalities, which are defined for highest order correlation functions. A homogenization leads to inequalities involving more settings, that is a choice of one more observable is possible for each party. We show that this technique preserves the tightness of Bell inequalities: a homogenization of a tight CH-type Bell inequality is still a tight CHSH-type Bell inequality. As an example we obtain $3\times3\times3$ CHSH-type Bell inequalities by homogenization of $2\times 2\times 2$ CH-type Bell inequalities derived by Sliwa in [Phys. Lett. A {\bf 317}, 165 (2003)]