606 research outputs found
Semiclassical quantisation for a bosonic atom-molecule conversion system
We consider a simple quantum model of atom-molecule conversion where bosonic
atoms can combine into diatomic molecules and vice versa. The many-particle
system can be expressed in terms of the generators a deformed algebra,
and the mean-field dynamics takes place on a deformed version of the Bloch
sphere, a teardrop shaped surface with a cusp singularity. We analyse the
mean-field and many-particle correspondence, which shows typical features of
quantum-classical correspondence. We demonstrate that semiclassical methods can
be employed to recover full many-particle features from the mean-field
description in cold atom systems with atom-molecule conversion, and derive an
analytic expression for the many-particle density of states in the limit of
large particle numbers.Comment: 10 pages, 10 figures, corrected typos, further small changes, similar
to published versio
A Neural Attention Model for Abstractive Sentence Summarization
Summarization based on text extraction is inherently limited, but
generation-style abstractive methods have proven challenging to build. In this
work, we propose a fully data-driven approach to abstractive sentence
summarization. Our method utilizes a local attention-based model that generates
each word of the summary conditioned on the input sentence. While the model is
structurally simple, it can easily be trained end-to-end and scales to a large
amount of training data. The model shows significant performance gains on the
DUC-2004 shared task compared with several strong baselines.Comment: Proceedings of EMNLP 201
Propagation of Gaussian beams in the presence of gain and loss
We consider the propagation of Gaussian beams in a waveguide with gain and
loss in the paraxial approximation governed by the Schr\"odinger equation. We
derive equations of motion for the beam in the semiclassical limit that are
valid when the waveguide profile is locally well approximated by quadratic
functions. For Hermitian systems, without any loss or gain, these dynamics are
given by Hamilton's equations for the center of the beam and its conjugate
momentum. Adding gain and/or loss to the waveguide introduces a non-Hermitian
component, causing the width of the Gaussian beam to play an important role in
its propagation. Here we show how the width affects the motion of the beam and
how this may be used to filter Gaussian beams located at the same initial
position based on their width
Character-Aware Neural Language Models
We describe a simple neural language model that relies only on
character-level inputs. Predictions are still made at the word-level. Our model
employs a convolutional neural network (CNN) and a highway network over
characters, whose output is given to a long short-term memory (LSTM) recurrent
neural network language model (RNN-LM). On the English Penn Treebank the model
is on par with the existing state-of-the-art despite having 60% fewer
parameters. On languages with rich morphology (Arabic, Czech, French, German,
Spanish, Russian), the model outperforms word-level/morpheme-level LSTM
baselines, again with fewer parameters. The results suggest that on many
languages, character inputs are sufficient for language modeling. Analysis of
word representations obtained from the character composition part of the model
reveals that the model is able to encode, from characters only, both semantic
and orthographic information.Comment: AAAI 201
Classical and quantum dynamics in the (non-Hermitian) Swanson oscillator
The non-Hermitian quadratic oscillator studied by Swanson is one of the
popular -symmetric model systems. Here a full classical description of its
dynamics is derived using recently developed metriplectic flow equations, which
combine the classical symplectic flow for Hermitian systems with a dissipative
metric flow for the anti-Hermitian part. Closed form expressions for the metric
and phase-space trajectories are presented which are found to be periodic in
time. Since the Hamiltonian is only quadratic the classical dynamics exactly
describes the quantum dynamics of Gaussian wave packets. It is shown that the
classical metric and trajectories as well as the quantum wave functions can
diverge in finite time even though the -symmetry is unbroken, i.e., the
eigenvalues are purely real.Comment: extended version, accepted for publication in J. Phys.
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