No description available.

Thesis (Ph.D.) --University of Adelaide, School of Chemistry and Physics, Discipline of Physics, 2006. / "5 April 2006" Bibliography: pages 147-150. Also available in print form.

No description available.

In this thesis we shall be concerned with the study of models which arise as a consequence of adopting discrete regularisations for various Euclidean space quantum field theories. Specifically, we employ a random triangulation of the continuum space, and define the fields only over nodes or links of the mesh. Lattice field theories, together with the Renormalisation Group, are introduced in the first chapter. Continuum physics is shown to depend on the positions and stabilities of zeroes of the β-function, which in turn requires a knowledge of the critical behaviour of the associated statistical model. In Chapter 2. we examine a theory of Dirac fermions in 2 + 1 dimensions on a random lattice. We investigate the behaviour of the 2-pt function and fermion condensate in the absence of any background gauge field. The results indicate certain doubling problems, generic to regular lattice formulations of fermion field theories, are evaded, at least at tree graph level. We then go on to examine the fermion vacuum currents in the presence of background fields with non-zero winding number. We are able to demonstrate the existence of a Chern-Simon's topological term in the gauge field effective action which yields parity violating vacuum currents. The magnitude of these are in agreement with certain continuum calculations. The final chapter concerns the properties of random surfaces. The particular class of models chosen originate as discretisations of Polyakov's string. The partition function is approximated by a sum over all possible random triangulations and an integral over vertex positions. The sum over random lattices is intended to mimick the functional integral over intrinsic metrics encountered in the continuum, and the model may also be pictured as 2D quantum gravity coupled to a scalar field. We consider the phase structure of the models when two forms of extrinsic curvature are added to the standard action. Monte-Carlo simulation indicates that with one type of curvature term a strong 2^nd order phase transition exists at finite coupling, leading to a new continuum limit for the model possessing long-range correlation properties. With the other type a much weaker higher order transition is observed. In this case the surface will be crumpled at long distance. We discuss the implications of these results for continuum surfaces.

No description available.

Optical lattices make it possible to trap and coherently control large ensembles of ultracold atoms. They provide the possibility to create lattice potentials that mimic the structure of solid-state systems, and to control these potentials dynamically. In this thesis, we study how dynamical manipulations of the lattice geometry can be used to perform different tasks, ranging from quantum information processing to the creation of diatomic molecules. We first examine the dynamical properties of ultracold atoms trapped in a lattice whose periodicity is dynamically doubled. We derive a model describing the dynamics of the atoms during this process, and compute the different interaction parameters of this model. We investigate different ways of using this lattice manipulation to optimise the initialisation time of a Mott-insulating state with one atom per site, and provide a scaling law related to the interaction parameters of the system. We go on to show that entangling operations between the spin of adjacent atoms are realisable with optical lattices forming arrays of double-well potentials. We study the creation of a lattice containing a spin-encoded Bell-pair in each double-well, and show that resilient, highly-entangled many-body states are realisable using lattice manipulations. We show that the creation of cluster-like states encoded on Bell-pairs can be achieved using these systems, and we provide measurement networks that allow the execution of quantum algorithms while maintaining intact the resilience of the system. Finally, we investigate the possibility to create a diatomic molecular state and simulate Fermi systems via the excitation to Rydberg levels of ground-state atoms trapped in optical lattices. We develop a method based on symbolical manipulations to compute the interaction parameters between highly-excited electrons, and evaluate them for different electronic configurations. We use these parameters to investigate the existence of diatomic molecular states with equilibrium distances comparable to typical lattice spacings. Considering the possibility to excite atoms trapped in an optical lattice to Rydberg levels such that the electronic cloud of neighbouring atoms overlap, we propose a model describing their interactions and compute its parameters. If such systems were realised, they would allow the simulation of Fermi systems at a temperature much below the Fermi temperature, thus enabling the observation of quantum phenomena hitherto inaccessible with current technology.

Controlling fields and properties has attracted ever increasing interest over past decades due to the rapid advancement of nanofabrication techniques. In the field of nano-optics, to overcome the limit of signal processing speed and device scale of traditional electronic devices, optical devices using photon as the signal carriers have been chosen as the potential candidates. However, the diffraction limit of light has limited the integration of the micro-meter photonic components into electronic chips. Plasmonics offer the possibility to control electromagnetic fields at the subwavelength scale. Moreover , this controlling become tunable by introducing gradient into the material and/or structure, i.e., taking the concept of functionally graded materials (FGM) to design materials. / Gradon confinements in graded materials and/or systems open a door for tunable fields-controlling, which have potential applications in a variety of fields. Our research methods and results provide an effective way to understand field localization in a variety of systems, and they can be applied to design and manufacture thermal devices and even on-chip plasmonic-optical devices. / Gradon confinements, or referred as frequency-controlled localization of fields are investigated in various graded plasmonic lattices. The correspondences between gradon confinements and Bloch oscillations as well as nonBloch oscillations are explored. By taking into account retardation and loss effects, the asymmetric localization behavior and broadband localizat ion due to graded host permittivity are studied. / This thesis will concentrate on gradon confinements, which make controlling fields and properties tunable in graded materials and/or systems. We start with investigating gradon modes and their properties in graded elastic lattices. Using the quantum-classical analogue method, the analytic envelope function is obtained and can be used to analyze the system-size dependence of inverse participation ratio of gradon modes. In damping graded elastic lattices , the frequency-dependent behavior of relaxation rate are studied analytically and numerically. / We continue to study the three-dimensional graded plasmonic lattices with fully retarded electromagnetic interactions. A generalized Ewald-Kornfeld summation formula is developed to deal with the long-range interaction. In the quasistatic limit, various plasmonic gradon modes are investigated. Taking retardation and loss into account, field localization and enhancement are calculated in three-dimensional graded plasmonic lattices with graded size, spacing, and/or host permittivity in one direction. / Zheng, Mingjie = 弹性和等离子体梯度子禁闭研究 / 郑明杰. / Adviser: Kin Wah Yu. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 117-124) and index. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Zheng, Mingjie = Tan xing he deng li zi ti ti du zi jin bi yan jiu / Zheng Mingjie.

We study scalar-fermion models with Yukawa interaction on a space-time lat- tice. Such models can describe the Higgs sector of the Standard Model in the case when the Higgs particle is very heavy (few hundred GeV) and there are very heavy fermions whose masses are due to their Yukawa interactions with the Higgs field. We study a realistic model with four component scalar field as well as simplified models with one and two component scalar fields. We use a mean field approximation to calculate equations for critical lines in the large d (dimension of space-time) limit. These lines are in very good agreement with available Monte Carlo data for the models at d = 4. We calculate fermion correlation functions in the mean field and large d approximations to study properties of different phases in the lattice models. We find two distinct phases with vanishing expectation values of the scalar field. One (at small Yukawa coupling Y) contains massless fermions, while in the other (at large F) the fermions have masses larger than the scale given by the inverse lattice spacing. We find that in the latter phase fermions can form bosonic bound states. These states show up as poles in a four-fermion correlator. We discuss pos- sible continuum limits in the lattice scalar-fermion models. In particular, we show that a theory defined near the critical line separating the disordered phase from the phase with antiferromagnetic order is not unitary.

Thesis (Ph.D.)--York University, 2007. Graduate Programme in Physics and Astronomy. / Typescript. Includes bibliographical references (leaves 211-217). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR29346

No description available.