Massive Quantum Memories by Periodically Inverted Dynamic Evolutions

We introduce a general scheme to realize perfect quantum state reconstruction and storage in systems of interacting qubits. This novel approach is based on the idea of controlling the residual interactions by suitable external controls that, acting on the inter-qubit couplings, yield time-periodic inversions in the dynamical evolution, thus cancelling exactly the effects of quantum state diffusion. We illustrate the method for spin systems on closed rings with XY residual interactions, showing that it enables the massive storage of arbitrarily large numbers of local states, and we demonstrate its robustness against several realistic sources of noise and imperfections.Comment: 10 pages, 3 figures. Contribution to the Proceedings of the Workshop on "Quantum entanglement in physical and information sciences", held in Pisa, December 14-18, 200

Probing particle and nuclear physics models of neutrinoless double beta decay with different nuclei

Half-life estimates for neutrinoless double beta decay depend on particle physics models for lepton flavor violation, as well as on nuclear physics models for the structure and transitions of candidate nuclei. Different models considered in the literature can be contrasted - via prospective data - with a "standard" scenario characterized by light Majorana neutrino exchange and by the quasiparticle random phase approximation, for which the theoretical covariance matrix has been recently estimated. We show that, assuming future half-life data in four promising nuclei (Ge-76, Se-82, Te-130, and Xe-136), the standard scenario can be distinguished from a few nonstandard physics models, while being compatible with alternative state-of-the-art nuclear calculations (at 95% C.L.). Future signals in different nuclei may thus help to discriminate at least some decay mechanisms, without being spoiled by current nuclear uncertainties. Prospects for possible improvements are also discussed.Comment: Minor corrections in the text, references added. Matches published version in Phys. Rev. D 80, 015024 (2009

Campaign individualization in comparative perspective: does the context matter?

Despite a great flourishing of studies on election campaigns, the issue of individualized campaigns has been widely neglected, especially from a comparative perspective. Yet, campaigns differ not only in terms of strategy or style, but also with regard to the role played by individual candidates. This article examines the variation of both the communicative focus and the resources used by candidates across different Western democracies. Using data from the Comparative Candidate Surveys (CCS), it tests the impact of several institutional and political features on campaign individualization. Our results show that both electoral systems and the legal framework regulating electoral contests display a significant impact on campaign individualization.info:eu-repo/semantics/publishedVersio

Northern JHK Standard Stars for Array Detectors

We report J, H and K photometry of 86 stars in 40 fields in the northern hemisphere. The fields are smaller than or comparable to a 4x4 arcmin field-of-view, and are roughly uniformly distributed over the sky, making them suitable for a homogeneous broadband calibration network for near-infrared panoramic detectors. K magnitudes range from 8.5 to 14, and J-K colors from -0.1 to 1.2. The photometry is derived from a total of 3899 reduced images; each star has been measured, on average, 26.0 times per filter on 5.5 nights. Typical errors on the photometry are about 0.012.Comment: 10 pages including 3 figures, one separate figure on four pages. The finding chart of the AS-30 field and a few coordinates have been corrected. GIF finding charts can also be found at http://www.arcetri.astro.it/~hunt/std.htm

Neutrino Decay and Atmospheric Neutrinos

We reconsider neutrino decay as an explanation for atmospheric neutrino observations. We show that if the mass-difference relevant to the two mixed states \nu_\mu and \nu_\tau is very small (< 10^{-4} eV^2), then a very good fit to the observations can be obtained with decay of a component of \nu_\mu to a sterile neutrino and a Majoron. We discuss how the K2K and MINOS long-baseline experiments can distinguish the decay and oscillation scenarios.Comment: 9 pages, Revtex, uses epsf.sty, 3 postscript figures. Additions and corrections to references, minor changes in the text and to some number

Unification of gravity, gauge fields, and Higgs bosons

We consider a diffeomorphism invariant theory of a gauge field valued in a Lie algebra that breaks spontaneously to the direct sum of the spacetime Lorentz algebra, a Yang-Mills algebra, and their complement. Beginning with a fully gauge invariant action -- an extension of the Plebanski action for general relativity -- we recover the action for gravity, Yang-Mills, and Higgs fields. The low-energy coupling constants, obtained after symmetry breaking, are all functions of the single parameter present in the initial action and the vacuum expectation value of the Higgs.Comment: 12 pages, no figures. v2 minor correction

Geometric Effects and Computation in Spin Networks

When initially introduced, a Hamiltonian that realises perfect transfer of a quantum state was found to be analogous to an x-rotation of a large spin. In this paper we extend the analogy further to demonstrate geometric effects by performing rotations on the spin. Such effects can be used to determine properties of the chain, such as its length, in a robust manner. Alternatively, they can form the basis of a spin network quantum computer. We demonstrate a universal set of gates in such a system by both dynamical and geometrical means

Oscillations of solar atmosphere neutrinos

The Sun is a source of high energy neutrinos (E > 10 GeV) produced by cosmic ray interactions in the solar atmosphere. We study the impact of three-flavor oscillations (in vacuum and in matter) on solar atmosphere neutrinos, and calculate their observable fluxes at Earth, as well as their event rates in a kilometer-scale detector in water or ice. We find that peculiar three-flavor oscillation effects in matter, which can occur in the energy range probed by solar atmosphere neutrinos, are significantly suppressed by averaging over the production region and over the neutrino and antineutrino components. In particular, we find that the relation between the neutrino fluxes at the Sun and at the Earth can be approximately expressed in terms of phase-averaged ``vacuum'' oscillations, dominated by a single mixing parameter (the angle theta_23).Comment: v2: 11 pages, 8 eps figures. Content added (Sec. III D and Fig. 6), references updated. Matches the published versio

Engineering massive quantum memories by topologically time-modulated spin rings

We introduce a general scheme to realize perfect storage of quantum information in systems of interacting qubits. This novel approach is based on {\it global} external controls of the Hamiltonian, that yield time-periodic inversions in the dynamical evolution, allowing a perfect periodic quantum state recontruction. We illustrate the method in the particularly interesting and simple case of spin systems affected by XY residual interactions with or without static imperfections. The global control is achieved by step time-inversions of an overall topological phase of the Aharonov-Bohm type. Such a scheme holds both at finite size and in the thermodynamic limit, thus enabling the massive storage of arbitrarily large numbers of local states, and is stable against several realistic sources of noise and imperfections.Comment: 12 pages, 9 figure