1,214 research outputs found
Spectral Analysis of a Four Mode Cluster State
We theoretically evaluate the squeezed joint operators produced in a single
optical parametric oscillator which generates quadripartite entangled outputs,
as demonstrated experimentally by Pysher et al. \cite{pysher}[Phys. Rev. Lett.
107, 030505 (2011)]. Using a linearized fluctuation analysis we calculate the
squeezing of the joint quadrature operators below threshold for a range of
local oscillator phases and frequencies. These results add to the existing
theoretical understanding of this potentially important system.Comment: 4 pages, 6 figure
Formative versus reflective measurement models: Two applications of formative measurement
This paper presents a framework that helps researchers to design and validate both formative and reflective measurement models. The framework draws from the existing literature and includes both theoretical and empirical considerations. Two important examples, one from international business and one from marketing, illustrate the use of the framework. Both examples concern constructs that are fundamental to theory-building in these disciplines, and constructs that most scholars measure reflectively. In contrast, applying the framework suggests that a formative measurement model may be more appropriate. These results reinforce the need for all researchers to justify, both theoretically and empirically, their choice of measurement model. Use of an incorrect measurement model undermines the content validity of constructs, misrepresents the structural relationships between them, and ultimately lowers the usefulness of management theories for business researchers and practitioners. The main contribution of this paper is to question the unthinking assumption of reflective measurement seen in much of the business literature
Quadripartite continuous-variable entanglement via quadruply concurrent downconversion
We investigate an intra-cavity coupled down-conversion scheme to generate
quadripartite entanglement using concurrently resonant nonlinearities. We
verify that quadripartite entanglement is present in this system by calculating
the output fluctuation spectra and then considering violations of optimized
inequalities of the van Loock-Furusawa type. The entanglement characteristics
both above and below the oscillation threshold are considered. We also present
analytic solutions for the quadrature operators and the van Loock-Furusawa
correlations in the undepleted pump approximation.Comment: 9 pages, 5 figure
A comparative study of dynamical simulation methods for the dissociation of molecular Bose-Einstein condensates
We describe a pairing mean-field theory related to the
Hartree-Fock-Bogoliubov approach, and apply it to the dynamics of dissociation
of a molecular Bose-Einstein condensate (BEC) into correlated bosonic atom
pairs. We also perform the same simulation using two stochastic phase-space
techniques for quantum dynamics -- the positive P-representation method and the
truncated Wigner method. By comparing the results of our calculations we are
able to assess the relative strength of these theoretical techniques in
describing molecular dissociation in one spatial dimension. An important aspect
of our analysis is the inclusion of atom-atom interactions which can be
problematic for the positive-P method. We find that the truncated Wigner method
mostly agrees with the positive-P simulations, but can be simulated for
significantly longer times. The pairing mean-field theory results diverge from
the quantum dynamical methods after relatively short times.Comment: 11 pages, 7 figures, corrected typos, minor content change
Analysis of a continuous-variable quadripartite cluster state from a single optical parametric oscillator
We examine the feasibility of generating continuous-variable multipartite
entanglement in an intra-cavity quadruply concurrent downconversion scheme that
has been proposed for the generation of cluster states by Menicucci \textit{et
al.} [Physical Review Letters \textbf{101}, 130501 (2008)]. By calculating
optimized versions of the van Loock-Furusawa correlations we demonstrate
genuine quadripartite entanglement and investigate the degree of entanglement
present. Above the oscillation threshold the basic cluster state geometry under
consideration suffers from phase diffusion. We alleviate this problem by
incorporating a small injected signal into our analysis. Finally, we
investigate squeezed joint operators. While the squeezed joint operators
approach zero in the undepleted regime, we find that this is not the case when
we consider the full interaction Hamiltonian and the presence of a cavity. In
fact, we find that the decay of these operators is minimal in a cavity, and
even depletion alone inhibits cluster state formation.Comment: 26 pages, 12 figure
Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Special Report of the Intergovernmental Panel on Climate Change
This Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) has been jointly coordinated by Working Groups I (WGI) and II (WGII) of the Intergovernmental Panel on Climate Change (IPCC). The report focuses on the relationship between climate change and extreme weather and climate events, the impacts of such events, and the strategies to manage the associated risks. The IPCC was jointly established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), in particular to assess in a comprehensive, objective, and transparent manner all the relevant scientific, technical, and socioeconomic information to contribute in understanding the scientific basis of risk of human-induced climate change, the potential impacts, and the adaptation and mitigation options. Beginning in 1990, the IPCC has produced a series of Assessment Reports, Special Reports, Technical Papers, methodologies, and other key documents which have since become the standard references for policymakers and scientists.This Special Report, in particular, contributes to frame the challenge of dealing with extreme weather and climate events as an issue in decisionmaking under uncertainty, analyzing response in the context of risk management. The report consists of nine chapters, covering risk management; observed and projected changes in extreme weather and climate events; exposure and vulnerability to as well as losses resulting from such events; adaptation options from the local to the international scale; the role of sustainable development in modulating risks; and insights from specific case studies
Absence of charge-density-wave sliding in epitaxial charge-ordered Pr0.48Ca0.52MnO3 films
For an epitaxial Pr0.48Ca0.52MnO3 film on NdGaO3, we use transmission
electron microscopy to observe a "charge-ordered" superlattice along the
in-plane direction a. The same film shows no electrical signatures of charge
order. The in-plane electrical anisotropy (rho)a/(rho)c = 28 is constant, and
there is no evidence of sliding charge density waves up to the large field of
~10^3 V/cm.Comment: 8 pages, 3 figure
Effects of Magnetic Order on the Upper Critical Field of UPt
I present a Ginzburg-Landau theory for hexagonal oscillations of the upper
critical field of UPt near . The model is based on a
representation for the superconducting order parameter,
, coupled to an in-plane AFM order parameter,
. Hexagonal anisotropy of arises from the weak in-plane
anisotropy energy of the AFM state and the coupling of the superconducting
order parameter to the staggered field. The model explains the important
features of the observed hexagonal anisotropy [N. Keller, {\it et al.}, Phys.
Rev. Lett. {\bf 73}, 2364 (1994).] including: (i) the small magnitude, (ii)
persistence of the oscillations for , and (iii) the change in
sign of the oscillations for and (the temperature at the
tetracritical point). I also show that there is a low-field crossover
(observable only very near ) below which the oscillations should vanish.Comment: 9 pages in a RevTex (3.0) file plus 2 postscript figures (uuencoded).
Submitted to Physical Review B (December 20, 1994)
- …