1,467 research outputs found
Asymmetric double barrier resonant tunneling structures with improved characteristics
We present a self-consistent calculation, based on the global coherent
tunnelling model, and show that structural asymmetry of double barrier resonant
tunnelling structures significantly modifies the current-voltage
characteristics compared to the symmetric structures. In particular, a suitably
designed asymmetric structure can produce much larger peak current and absolute
value of the negative differential conductivity than its commonly used
symmetric counterpart.Comment: 1 paper, 3 figure
A gauge model for quantum mechanics on a stratified space
In the Hamiltonian approach on a single spatial plaquette, we construct a
quantum (lattice) gauge theory which incorporates the classical singularities.
The reduced phase space is a stratified K\"ahler space, and we make explicit
the requisite singular holomorphic quantization procedure on this space. On the
quantum level, this procedure furnishes a costratified Hilbert space, that is,
a Hilbert space together with a system which consists of the subspaces
associated with the strata of the reduced phase space and of the corresponding
orthoprojectors. The costratified Hilbert space structure reflects the
stratification of the reduced phase space. For the special case where the
structure group is , we discuss the tunneling probabilities
between the strata, determine the energy eigenstates and study the
corresponding expectation values of the orthoprojectors onto the subspaces
associated with the strata in the strong and weak coupling approximations.Comment: 38 pages, 9 figures. Changes: comments on the heat kernel and
coherent states have been adde
Bell-inequality violation with "thermal" radiation
The model of a quantum-optical device for a conditional preparation of
entangled states from input mixed states is presented. It is demonstrated that
even thermal or pseudo-thermal radiation can be entangled in such a way, that
Bell-inequalities are violated
Dissipative Liouville Cosmology: A Case Study
We consider solutions of the cosmological equations pertaining to a
dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which
may describe the effective field theoretic limit of a non-critical string model
of the Universe. The non-criticality may be the result of an early-era
catastrophic cosmic event, such as a big-bang, brane-world collision etc. The
evolution of the various cosmological parameters of the model are obtained, and
the effects of the dilaton and off-shell Liouville terms, including briefly
those on relic densities, which distinguish the model from conventional
cosmologies, are emphasised.Comment: 19 pages latex, 11 eps figures incorporate
Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards
We present a simple method to stabilize the optical path length of an optical
fiber to an accuracy of about 1/100 of the laser wavelength. We study the
dynamic response of the path length to modulation of an electrically conductive
heater layer of the fiber. The path length is measured against the laser
wavelength by use of the Pound-Drever-Hall method; negative feedback is applied
via the heater. We apply the method in the context of a cryogenic resonator
frequency standard.Comment: Expanded introduction and outlook. 9 pages, 5 figure
The role of interparticle heterogeneities in the selenization pathway of Cu Zn Sn S nanoparticle thin films a real time study
Real time energy dispersive X ray diffraction EDXRD analysis has been utilized to observe the selenization of Cu Zn Sn S nanoparticle films coated from three nanoparticle populations Cu and Sn rich particles roughly 5 nm in size, Zn rich nanoparticles ranging from 10 to 20 nm in diameter, and a mixture of both types of nanoparticles roughly 1 1 by mass , which corresponds to a synthesis recipe yielding CZTSSe solar cells with reported total area efficiencies as high as 7.9 . The EDXRD studies presented herein show that the formation of copper selenide intermediates during the selenization of mixed particle films can be primarily attributed to the small, Cu and Sn rich particles. Moreover, the formation of these copper selenide phases represents the first stage of the CZTSSe grain growth mechanism. The large, Zn rich particles subsequently contribute their composition to form micrometer sized CZTSSe grains. These findings enable further development of a previously proposed selenization pathway to account for the roles of interparticle heterogeneities, which in turn provides a valuable guide for future optimization of processes to synthesize high quality CZTSSe absorber layer
Epistemic policy networks in the European Union’s CBRN risk mitigation policy
This paper offers insights into an innovative and currently flagship approach of the European Union (EU) to the mitigation of chemical, biological, radiological, and nuclear (CBRN) risks. Building on its long-time experience in the CBRN field, the EU has incorporated methods familiar to the students of international security governance: it is establishing regional networks of experts and expertise. CBRN Centers of Excellence, as they are officially called, aim to contribute to the security and safety culture in different parts of Africa, the Middle East, South East Asia, and South East Europe, in the broadly construed CBRN area. These regional networks represent a modern form of security cooperation, which can be conceptualized as an epistemic policy networks approach. It offers flexibility to the participating states, which have different incentives to get involved. At the same, however, the paper identifies potential limitations and challenges of epistemic policy networks in this form
Generation of entangled coherent states via cross phase modulation in a double electromagnetically induced transparency regime
The generation of an entangled coherent state is one of the most important
ingredients of quantum information processing using coherent states. Recently,
numerous schemes to achieve this task have been proposed. In order to generate
travelling-wave entangled coherent states, cross phase modulation, optimized by
optical Kerr effect enhancement in a dense medium in an electromagnetically
induced transparency (EIT) regime, seems to be very promising. In this
scenario, we propose a fully quantized model of a double-EIT scheme recently
proposed [D. Petrosyan and G. Kurizki, {\sl Phys. Rev. A} {\bf 65}, 33833
(2002)]: the quantization step is performed adopting a fully Hamiltonian
approach. This allows us to write effective equations of motion for two
interacting quantum fields of light that show how the dynamics of one field
depends on the photon-number operator of the other. The preparation of a
Schr\"odinger cat state, which is a superposition of two distinct coherent
states, is briefly exposed. This is based on non-linear interaction via
double-EIT of two light fields (initially prepared in coherent states) and on a
detection step performed using a beam splitter and two photodetectors.
In order to show the entanglement of a generated entangled coherent state, we
suggest to measure the joint quadrature variance of the field. We show that the
entangled coherent states satisfy the sufficient condition for entanglement
based on quadrature variance measurement. We also show how robust our scheme is
against a low detection efficiency of homodyne detectors.Comment: 15 pages, 9 figures; extensively revised version; added Section
Quantum non-demolition (QND) modulation of quantum interference
We propose an experiment where quantum interference between two different
paths is modulated by means of a QND measurement on one or both the arm of the
interferometer. The QND measurement is achieved in a Kerr cell. We illustrate a
scheme for the realisation of this experiment and some further developments.Comment: accepted for publicatio
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