1,293 research outputs found
A Berger type normal holonomy theorem for complex submanifolds
We prove a kind of Berger-Simons' Theorem for the normal holonomy group of a complex submanifold of the projective spac
Facilitated spin models of dissipative quantum glasses
We introduce a class of dissipative quantum spin models with local
interactions and without quenched disorder that show glassy behaviour. These
models are the quantum analogs of the classical facilitated spin models. Just
like their classical counterparts, quantum facilitated models display complex
glassy dynamics despite the fact that their stationary state is essentially
trivial. In these systems, dynamical arrest is a consequence of kinetic
constraints and not of static ordering. These models display a quantum version
of dynamic heterogeneity: the dynamics towards relaxation is spatially
correlated despite the absence of static correlations. Associated dynamical
fluctuation phenomena such as decoupling of timescales is also observed.
Moreover, we find that close to the classical limit quantum fluctuations can
enhance glassiness, as recently reported for quantum liquids.Comment: 7 pages, 6 figure
Creation of collective many-body states and single photons from two-dimensional Rydberg lattice gases
The creation of collective many-body quantum states from a two-dimensional
lattice gas of atoms is studied. Our approach relies on the van-der-Waals
interaction that is present between alkali metal atoms when laser excited to
high-lying Rydberg s-states. We focus on a regime in which the laser driving is
strong compared to the interaction between Rydberg atoms. Here energetically
low-lying many-particle states can be calculated approximately from a quadratic
Hamiltonian. The potential usefulness of these states as a resource for the
creation of deterministic single-photon sources is illustrated. The properties
of these photon states are determined from the interplay between the particular
geometry of the lattice and the interatomic spacing.Comment: 12 pages, 8 figure
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
Microstructural development and mechanical properties of iron based cermets processed by pressureless and spark plasma sintering
Iron-based cermets are an interesting class of metal-ceramic composites in which properties and the factors influencing them are to be explored. In this work the metal matrix contains Cr, W, Mo and V as alloying elements, and the hard phase is constituted by 50 vol% of titanium carbonitride (TiCN) particles. The work studies the influence of the C content and the processing method on the sinterability, microstructure and hardness of the developed cermet materials. For that purpose, cermet samples with different C content in the matrix (0 wt%, 0.25 wt%, 0.5 wt%, 1.0 wt%) were prepared by conventional pressureless sintering (CPS) and, in order to achieve finer microstructures and to reduce the sintering time, by spark plasma sintering (SPS). The density and hardness (HV30) of the processed materials was evaluated, while their phase composition and microstructure was characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The equilibrium phase diagram of the composite material was calculated by ThermoCalc software in order to elucidate the influence of the carbon content on the obtained phases and developed microstructures.The authors would like to acknowledge financial support from
the Spanish Ministry of Science and Innovation through the
R&D Project MAT2009-14448-C02 and the Comunidad de Madrid
through the program ESTRUMAT-CM (reference S2009/MAT-
1585). K. Vanmeensel thanks the Research Fund Flanders (FWO)
for his postdoctoral fellowship.Publicad
Requirements for Bend Insensitive Fiber in Millimeter-Wave Fronthaul Systems
The impact of fiber bending on mm-wave radio-over-fiber transmission is investigated and the need for bend insensitive fiber for front-haul installation confirmed. A 70m W-band hybrid photonic-wireless link including bend insensitive fiber is demonstrated with BER<10\u3csup\u3e-6\u3c/sup\u3e at 5mm bending radius
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