27,758 research outputs found
Quantum theory of structured monochromatic light
Applications that envisage utilizing the orbital angular momentum (OAM) at
the single photon level assume that the OAM degrees of freedom that the photons
inherit from the classical wave solutions are orthogonal. To test this critical
assumption, we quantize the beam-like solutions of the vector Helmholtz
equation from first principles to delineate its elementary quantum mechanical
degrees of freedom. We show that although the beam-photon operators do not in
general satisfy the canonical commutation relations, implying that the photon
states they create are not orthogonal, the states are nevertheless bona fide
eigenstates of the number and Hamiltonian operators. The explicit
representation for the photon operators presented in this work forms a natural
basis to study light-matter interactions and quantum information processing at
the single photon level
Analysis of thin-film structures with nuclear backscattering and x-ray diffraction
Backscattering of MeV ^(4)He ions and Seemann-Bohlin x-ray diffraction techniques have been used to study silicide formation on Si and SiO_2 covered with evaporated metal films. Backscattering techniques provide information on the composition of thin-film structures as a function of depth. The glancing-angle x-ray technique provides identification of phases and structural information. Examples are given of V on Si and on SiO_2 to illustrate the major features of these analysis techniques. We also give a general review of recent studies of silicide formation
Synthesis and control of generalised dynamically substructured systems
The experimental technique for testing engineering systems via the method of dynamic substructuring is receiving significant global interest, for example in the fields of large-scale structural, aerospace, and automotive system testing. Dynamically substructured systems (DSSs) enable full-size, critical components of a complete system to be physically tested in real-time, within a laboratory environment, while the remainder of the system is modelled numerically. The intention is that the combined physical-numerical DSS behaves as if it were the complete (or emulated) system.In an ideal mechanical DSS, for example, perfect synchronization of displacements and forces at the interfaces between the numerical and physical components (or substructures) is required. Hence, a key design feature of successful DSS systems is the high fidelity of the control action. Equally, a DSS controller must be able to cope with non-linear, time-varying, and uncertain parameters within the physical substructure dynamics.The main purpose of this paper is to present a generalized DSS framework, together with associated linear and adaptive control strategies, that are specifically tailored to achieve high synchronization performance. The initial studies of this problem, as described in an earlier paper by Stoten and Hyde, are therefore continued by generalizing both the DSS dynamics and the control strategies to include (a) a number of newly defined modes of operation and (b) multivariable dynamics. In addition, comparative implementation and simulation studies are included, based upon the DSS testing of a mechanical system (a planar quasi-motorcycle rig), which was specifically designed to highlight the main features of this research. The comparative studies show that excellent DSS control can be achieved, especially with the addition of an adaptive component to the controller, despite significant changes to the physical substructure dynamics
Entanglement and SU(n) symmetry in one-dimensional valence bond solid states
Here we evaluate the many-body entanglement properties of a generalized SU(n)
valence bond solid state on a chain. Our results follow from a derivation of
the transfer matrix of the system which, in combination with symmetry
properties, allows for a new, elegant and straightforward evaluation of
different entanglement measures. In particular, the geometric entanglement per
block, correlation length, von Neumann and R\'enyi entropies of a block,
localizable entanglement and entanglement length are obtained in a very simple
way. All our results are in agreement with previous derivations for the SU(2)
case.Comment: 4 pages, 2 figure
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