9,650 research outputs found
Model for resonant photon creation in a cavity with time dependent conductivity
In an electromagnetic cavity, photons can be created from the vacuum state by
changing the cavity's properties with time. Using a simple model based on a
massless scalar field, we analyze resonant photon creation induced by the
time-dependent conductivity of a thin semiconductor film contained in the
cavity. This time dependence may be achieved by irradiating periodically the
film with short laser pulses. This setup offers several experimental advantages
over the case of moving mirrors.Comment: 9 pages, 1 figure. Minor changes. Version to appear in Phys. Rev.
Analysis of photon-atom entanglement generated by Faraday rotation in a cavity
Faraday rotation based on AC Stark shifts is a mechanism that can entangle
the polarization variables of photons and atoms. We analyze the structure of
such entanglement by using the Schmidt decomposition method. The
time-dependence of entanglement entropy and the effective Schmidt number are
derived for Gaussian amplitudes. In particular we show how the entanglement is
controlled by the initial fluctuations of atoms and photons.Comment: 6 pages, 3 figure
Polarization and frequency disentanglement of photons via stochastic polarization mode dispersion
We investigate the quantum decoherence of frequency and polarization
variables of photons via polarization mode dispersion in optical fibers. By
observing the analogy between the propagation equation of the field and the
Schr\"odinger equation, we develop a master equation under Markovian
approximation and analytically solve for the field density matrix. We identify
distinct decay behaviors for the polarization and frequency variables for
single-photon and two-photon states. For the single photon case, purity
functions indicate that complete decoherence for each variable is possible only
for infinite fiber length. For entangled two-photon states passing through
separate fibers, entanglement associated with each variable can be completely
destroyed after characteristic finite propagation distances. In particular, we
show that frequency disentanglement is independent of the initial polarization
status. For propagation of two photons in a common fiber, the evolution of a
polarization singlet state is addressed. We show that while complete
polarization disentanglement occurs at a finite propagation distance, frequency
entanglement could survive at any finite distance for gaussian states.Comment: 2 figure
Atomic layer deposition of ZnS nanotubes
We report on growth of high-aspect-ratio () zinc sulfide
nanotubes with variable, precisely tunable, wall thicknesses and tube diameters
into highly ordered pores of anodic alumina templates by atomic layer
deposition (ALD) at temperatures as low as 75 C. Various
characterization techniques are employed to gain information on the
composition, morphology, and crystal structure of the synthesized samples.
Besides practical applications, the ALD-grown tubes could be envisaged as model
systems for the study of a certain class of size-dependent quantum and
classical phenomena.Comment: 1 LaTeX source file, 8 eps figures, and the manuscript in PDF forma
An application of convolutional neural network in street image classification: The case study of London
Street frontage quality is an important element in urban design as it contributes to the interest, social life and success of public spaces. To collect the data needed to evaluate street frontage quality at the city or regional level using traditional survey method is both costly and time consuming. As a result, this research proposes a pipeline that uses convolutional neural network to classify the frontage of a street image through the case study of Greater London. A novelty of the research is it uses both Google streetview images and 3D-model generated streetview images for the classification. The benefit of this approach is that it can provide a framework to test different urban parameters to help evaluate future urban design projects. The research finds encouraging results in classifying urban frontage quality using deep learning models. This research also finds that augmenting the baseline model with images produced from a 3D-model can improve slightly the accuracy of the results. However these results should be taken as preliminary, where we acknowledge several limitations such as the lack of adversarial analysis, labeled data, or parameter tuning. Despite these limitations, the results of the proof-of-concept study is positive and carries great potential in the application of urban data analytics
Development of a new machine system for the forming of micro-sheet-products
Most of the developed micro-forming machines were based on standalone concepts which do not support efficient integration to make them fully automated and integrated. At present, material feeding in micro-forming is not of sufficient precision and reliability for high throughput manufacturing applications. Precise feeding is necessary to ensure that micro-parts can be produced with sufficient accuracy, especially in multi-stage forming, while high-speed feeding is a must to meet the production-rate requirements. Therefore, design of a new high-precision and high-speed feeder for micro-forming is proposed. Several possible approaches are examined with a view to establishing feasible concepts. Based on the investigation, several concepts for thin sheet-metal feeding for micro-forming are generated, they being argued and assessed with applicable loads and forces analysis. These form a basis of designing a new feeder
The links between magnetic fields and filamentary clouds III: field regulated mass cumulative functions
During the past decade the dynamical importance of magnetic fields in
molecular clouds has been increasingly recognized, as observational evidence
has accumulated. However, how a magnetic field affect star formation is still
unclear. Typical star formation models still treat a magnetic fields as an
isotropic pressure, ignoring the fundamental property of dynamically important
magnetic fields: their direction. This study builds on our previous work which
demonstrated how the mean magnetic field orientation relative to the global
cloud elongation can affect cloud fragmentation. After the linear mass
distribution reported earlier, we show here that the mass cumulative function
(MCF) of a cloud is also regulated by the field orientation. A cloud elongated
closer to the field direction tends to have a shallower MCF, in other words, a
higher portion of the gas in high density. The evidence is consistent with our
understanding of bimodal star formation efficiency discovered earlier, which is
also correlated with the field orientations.Comment: Accepted by MNRAS on 11 August 202
Quantum fluctuations in coupled dark solitons in trapped Bose-Einstein condensates
We show that the quantum fluctuations associated with the Bogoliubov
quasiparticle vacuum can be strongly concentrated inside dark solitons in a
trapped Bose Einstein condensate. We identify a finite number of anomalous
modes that are responsible for such quantum phenomena. The fluctuations in
these anomalous modes correspond to the `zero-point' oscillations in coupled
dark solitons.Comment: 4 pages, 3 figure
Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas
We examine the basic mode structure of atomic Cooper pairs in an
inhomogeneous Fermi gas. Based on the properties of Bogoliubov quasi-particle
vacuum, the single particle density matrix and the anomalous density matrix
share the same set of eigenfunctions. These eigenfunctions correspond to
natural pairing orbits associated with the BCS ground state. We investigate
these orbits for a Fermi gas in a spherical harmonic trap, and construct the
wave function of a Cooper pair in the form of Schmidt decomposition. The issue
of spatial quantum entanglement between constituent atoms in a pair is
addressed.Comment: 14 pages, 4 figures, submitted to Phys. Rev.
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