9,490,578 research outputs found

    Effect of topology on the transport properties of two interacting dots

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    The transport properties of a system of two interacting dots, one of them directly connected to the leads constituting a side-coupled configuration (SCD), are studied in the weak and strong tunnel-coupling limits. The conductance behavior of the SCD structure has new and richer physics than the better studied system of two dots aligned with the leads (ACD). In the weak coupling regime and in the case of one electron per dot, the ACD configuration gives rise to two mostly independent Kondo states. In the SCD topology, the inserted dot is in a Kondo state while the side-connected one presents Coulomb blockade properties. Moreover, the dot spins change their behavior, from an antiferromagnetic coupling to a ferromagnetic correlation, as a consequence of the interaction with the conduction electrons. The system is governed by the Kondo effect related to the dot that is embedded into the leads. The role of the side-connected dot is to introduce, when at resonance, a new path for the electrons to go through giving rise to the interferences responsible for the suppression of the conductance. These results depend on the values of the intra-dot Coulomb interactions. In the case where the many-body interaction is restricted to the side-connected dot, its Kondo correlation is responsible for the scattering of the conduction electrons giving rise to the conductance suppression

    Scalable Ion Trap Quantum Computing without Moving Ions

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    A hybrid quantum computing scheme is studied where the hybrid qubit is made of an ion trap qubit serving as the information storage and a solid-state charge qubit serving as the quantum processor, connected by a superconducting cavity. In this paper, we extend our previous work [1] and study the decoherence, coupling and scalability of the hybrid system. We present our calculations of the decoherence of the coupled ion - charge system due to the charge fluctuations in the solid-state system and the dissipation of the superconducting cavity under laser radiation. A gate scheme that exploits rapid state flips of the charge qubit to reduce decoherence by the charge noise is designed. We also study a superconducting switch that is inserted between the cavity and the charge qubit and provides tunable coupling between the qubits. The scalability of the hybrid scheme is discussed together with several potential experimental obstacles in realizing this scheme

    Hund's coupling and the metal-insulator transition in the two-band Hubbard model

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    The Mott-Hubbard metal-insulator transition is investigated in a two-band Hubbard model within dynamical mean-field theory. To this end, we use a suitable extension of Wilson's numerical renormalization group for the solution of the effective two-band single-impurity Anderson model. This method is non-perturbative and, in particular, allows to take into account the full exchange part of the Hund's rule coupling between the two orbitals. We discuss in detail the influence of the various Coulomb interactions on thermodynamic and dynamic properties, for both the impurity and the lattice model. The exchange part of the Hund's rule coupling turns out to play an important role for the physics of the two-band Hubbard model and for the nature of the Mott-transition

    Probing dense and hot matter with low-mass dileptons and photons

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    Results on low-mass dileptons, covering the very broad energy range from the BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by the intriguing results obtained so far and the prospects for addressing them in the near future with the second generation of experiments, in particular HADES, NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference, Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published in Eur. Phys. J. C. The orginal version is available at www.springerlink.co

    Geometric Phase of a qubit interacting with a squeezed-thermal bath

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    We study the geometric phase of an open two-level quantum system under the influence of a squeezed, thermal environment for both non-dissipative as well as dissipative system-environment interactions. In the non-dissipative case, squeezing is found to have a similar influence as temperature, of suppressing geometric phase, while in the dissipative case, squeezing tends to counteract the suppressive influence of temperature in certain regimes. Thus, an interesting feature that emerges from our work is the contrast in the interplay between squeezing and thermal effects in non-dissipative and dissipative interactions. This can be useful for the practical implementation of geometric quantum information processing. By interpreting the open quantum effects as noisy channels, we make the connection between geometric phase and quantum noise processes familiar from quantum information theory.Comment: Accepted for publication in Eur. Phys. J. D; slightly abridged version of v2; 10 pages, 12 figure

    On relativistic approaches to the pion self-energy in nuclear matter

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    We argue that, in contrast to the non-relativistic approach, a relativistic evaluation of the nucleon--hole and delta-isobar--nucleon hole contributions to the pion self-energy incorporates the s-wave scattering, which requires a more accurate evaluation. Therefore relativistic approach containing only these diagrams does not describe appropriately the pion self-energy in isospin symmetric nuclear matter. We conclude that, a correct relativistic approach to the pion self-energy should involve a more sophisticated calculation in order to satisfy the known experimental results on the near-threshold behaviour of the pion-nucleon (forward) scattering amplitude.Comment: 7 pages,1 figur

    Strange particle production in proton-proton collisions at s=0.9\sqrt{s}=0.9 TeV with ALICE at the LHC

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    The production of mesons containing strange quarks (Ks0^0_s, ϕ\phi) and both singly and doubly strange baryons (Λ\Lambda, Anti-Λ\Lambda, and Ξ\Xi+Anti-Ξ\Xi) are measured at central rapidity in pp collisions at s\sqrt{s} = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at central rapidities for inelastic pp collisions are presented. For mesons, we report yields () of 0.184 ±\pm 0.002 stat. ±\pm 0.006 syst. for Ks0^0_s and 0.021 ±\pm 0.004 stat. ±\pm 0.003 syst. for ϕ\phi. For baryons, we find = 0.048 ±\pm 0.001 stat. ±\pm 0.004 syst. for Λ\Lambda, 0.047 ±\pm 0.002 stat. ±\pm 0.005 syst. for Anti-Λ\Lambda and 0.0101 ±\pm 0.0020 stat. ±\pm 0.0009 syst. for Ξ\Xi+Anti-Ξ\Xi. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.Comment: 33 pages, 21 captioned figures, 10 tables, authors from page 28, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/387

    Criminal liability of employees of financial intermediaries for money laundering: a British perspective

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    The money laundering rules, both those contained in the Proceeds of Crime Act 2002 (and the legislation which preceded it) and the provisions of the Money Laundering Regulations 1993, impose considerable liabilities not just on institutions but on their individual officers and employees. Although the Money Laundering Reporting Officer / Compliance Officer has particular responsibilities, this does not absolve the other employees of the firm from the requirement to exercise considerable diligence on their own account
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