Spring/Summer 2011 seminars
Department of Physics - Miramare
8th June, 15:00 - Room 2004
The Geometry of uantization: 2
In this second seminar we will show that Classical Mechanics and Quantum Mechanics can have the same functional form with the difference given only by the form of a metric living in a super-extension of time. These metrics are not unique but present a 10-paramers and a 15-parameters freedom for respectively Classical and Quantum Mechanics. The ones associated to Quantum mechanics have clearly a dependence on the Planck constant and need a regularization.
1st June, 15:00 - Room 204
The Geometry of quantization: 1
In this seminar we will try to pedagogically review the operatorial approach to classical mechanics pioneered in the 30's by Koopman and von Neumann and its more recent functional counterpart. Next we shall show that, via these tools, quantization can be achieved by a sort of dimensional reduction which surprisingly turns out to be nothing else than the functional counterpart of Geometric Quantization.
11th May, 15:00 - Room 204
GIACOMO OLIVIERO DOVIER
Electroweak corrections to semi-inclusive bottom Higgs production at the
LHC in the MSSM
Associated bottom-Higgs production in the MSSM is enhanced for a high tan(beta) scenario, making the process an interesting candidate for the discovery of supersymmetric Higgs particles at the LHC. One loop electroweak corrections to the cross section of the process can be very relevant, and can't be neglected, although some simpler approximation to the full correction could be needed for event generators. Furthermore, the study of this channel can be used to discriminate between a full MSSM and a single Higgs or Two Higgs Doublet Standard Model scenarios.
27th April, 15:00 - Room 204
The birth of entanglement in the interference of Gaussian states:
the role of the fidelity
At the hearth of quantum technology there is entanglement. Indeed, during the last two decades much attention has been devoted to the generation and the characterization of entanglement in bipartite and multi-partite systems. In the realm of continuous variables, attention has been focused to Gaussian states. Among the the possible mechanisms to generate Gaussian entanglement, the one consisting in the mixing of squeezed states at a beam splitter is of special interest in view of its feasibility. In this seminar we briefly review the interference of single photons at a beam splitter and the basic properties of the Gaussian states and operations. We then address the interaction of two Gaussian states interfering at a beam splitter and analyze the correlations exhibited by the resulting bipartite system. We show that nonlocal correlations (entanglement) arise if and only if the fidelity between the two input Gaussian states falls under a threshold value depending only on their purities and on the transmissivity of the beam splitter. Our result clarifies the role of squeezing as a prerequisite for entanglement and provides a tool to optimize the generation of entanglement by passive devices.
20th April, 15:00 - Room 204
Measuring electron sharing between atoms in first-priciple simulations
Calculations of large scale electron structure within periodic boundary conditions, mostly based on solid state physics, allow the modelling of atomic forces and molecular dynamics for atomic assemblies of 100-1000 atoms thus providing complementary information in material and macromolecular science. Nevertheless, these methods lack of connections with the chemistry of
simple molecules as isolated entities. In order to contribute to establish a conceptual connection between solid state physics and chemistry, the calculation of the extent of electron sharing between atoms, also known as delocalization index, is performed on simple molecules and on complexes with transition metal atoms, using density functional calculations where the Kohn-Sham molecular orbitals are represented in terms of plane-waves and in periodic boundary conditions. These applications show that the useful measure of electron sharing between atomic pairs can be easily recovered from density functional calculations using tha same set-up applied to large atomic assemblies in condensed phase, with no projections of molecular orbitals onto atomic orbitals.
13th April, 15:00 - Room 204
Top physics with the ATLAS detector at the LHC
The top quark, the heaviest known elementary particle of the Standard Model with a mass of 173 GeV, is copiously produced at the LHC, where two high intensity proton beams collide with a center of mass energy of 7 TeV. The properties of its production and decay can be studied by identifying and reconstructing its decay products. Thanks to the excellent performances of the ATLAS detector, which is able to identify and measure electrons, muons, hadronic jets, heavy flavour jets and neutrinos with a wide range of energies and an almost complete angular acceptance, the top
physics at ATLAS is now reaching high levels of precision, starting to compete with the Tevatron experiments CDF and D0.
The main results so far have been the measurements the production cross-section in the different production and decay channels (with the best precision reached in the top-antitop semi-leptonic channel). A measurement which can be of particular interest and which will be feasible within the end of the 2011 is the top-antitop angular production asymmetry in top-antitop pair production. The measurement of this quantity at both CDF and D0 shows a big discrepancy with the Standard Model prediction which is not yet understood. A confirmation of this discrepancy at the LHC can be the first clear signal of new physics beyond the Standard Model.
6th April, 15:00 - Luigi Stasi Seminar Room
Semiconductor nanowires: structural and electronic properties from first-principles calculations
Semiconductor nanowires (NWs) offer nowadays new perspectives for nanoelectronic devices. High- quality NWs can be experimentally grown: they are regularly shaped and nicely oriented, with wurzite (WZ) or zincblende (ZB) structure depending on the substrate and on the growth
conditions. Radial heterostructures, obtained depositing radially another semiconductor (shell) on a semiconductor NW (core), offer the possibility of further engineering their electronic properties by varying their geometric parameters.
After discussing the relative stability of pure ZB and WZ GaAs NWs, we extensively discuss the energetics of radial NWs made of InAs and GaAs with different core-shell composition, structure, thickness, shape, interfaces and exposed surfaces. We also discuss the most relevant electronic structure properties.
30th March, 15:00 - Room 204
Hydrogen molecules adsorbed on small transition metal clusters
Light complex hydrides of the type Am(MH4)n (A = Li, Na,Mg; M = Be, B, Al) as potential hydrogen storage materials have attracted much attention because of their high gravimetric hydrogen densities. However, their poor kinetics and lack of reversibility of hydrogen absorption/desorption reactions are the most critical problems for practical applications. The experimental results had indicated that the small size of the Ti clusters plays an important role in increasing the reaction rate of some of the hydrogen storage materials such as complex metal hydrides.
We perform first principles density functional theory calculations to investigate the geometric and electronic structures of Tin-mH2 (n=2-7, and m=1-22). By optimizing geometric structures, we obtain the saturated configurations for hydrogen storage on small Tin (n=2-7) clusters. Interestingly, we find that with an increase in the size of the Tin cluster, the effective space for each titanium atom to adsorb hydrogen molecules decreases, as does the maximum amount of hydrogen molecules adsorbed on each titanium atom. When the size of the Tin cluster goes beyond n=5, the maximum number of hydrogen molecules adsorbed on each Ti atom keeps a constant of 3. Furthermore, we suggest/propose that the hybridization of atomic orbitals in different atoms could be used to estimate the type of the bonds between the different atoms in clusters.
9th March, 15:00 - Room 204
On a recent proof of nonlocality without inequalities
We reconsider a recent derivation of the impossibility of reproducing by a local model all quantum predictions of a state of a single photon in a superposition of different locations. We call attention to the fact that, in spite of the validity of the conclusion, the argument presents various unsatisfactory aspects and does not put into the due evidence the fundamental and exclusive role of the request of locality. We show that by resorting to a recent way of dealing with nonlocality by resorting to set theoretic considerations one can derive the result in a way which is logically clean and parallels, with the necessary modifications, the line of thought followed by J. Bell in his celebrated paper.
Spring/Summer 2010 seminars
Spring/Summer 2009 seminars