5,219 research outputs found
Chiral topological states in Bose-Fermi mixtures
Topological states were initially discovered in solid state systems and have
generated widespread interest in many areas of physics. The advances in cold
atoms create novel settings for studying topological states that would be quite
unrealistic in solid state systems. One example is that the constituents of
quantum gases can be various types of bosons, fermions, and their mixtures.
This paper explores interaction-induced topological states in two-dimensional
Bose-Fermi mixture. We propose a class of topological states which have no
fractionalized excitations but possess maximally chiral edge states. For
previously known topological states, these two features can only be found
simultaneously in the integer quantum Hall states of fermions and the
state of bosons. The existences of some proposed states in certain continuum
and lattice models are corroborated by exact diagonalization and density matrix
renormalization group calculations. This paper suggests that Bose-Fermi mixture
is a very appealing platform for studying topological states.Comment: 10 pages, 8 figure
Bipartite Flat-Graph Network for Nested Named Entity Recognition
In this paper, we propose a novel bipartite flat-graph network (BiFlaG) for
nested named entity recognition (NER), which contains two subgraph modules: a
flat NER module for outermost entities and a graph module for all the entities
located in inner layers. Bidirectional LSTM (BiLSTM) and graph convolutional
network (GCN) are adopted to jointly learn flat entities and their inner
dependencies. Different from previous models, which only consider the
unidirectional delivery of information from innermost layers to outer ones (or
outside-to-inside), our model effectively captures the bidirectional
interaction between them. We first use the entities recognized by the flat NER
module to construct an entity graph, which is fed to the next graph module. The
richer representation learned from graph module carries the dependencies of
inner entities and can be exploited to improve outermost entity predictions.
Experimental results on three standard nested NER datasets demonstrate that our
BiFlaG outperforms previous state-of-the-art models.Comment: Accepted by ACL202
Emergent Fermi sea in a system of interacting bosons
An understanding of the possible ways in which interactions can produce
fundamentally new emergent many-body states is a central problem of condensed
matter physics. We ask if a Fermi sea can arise in a system of bosons subject
to contact interaction. Based on exact diagonalization studies and variational
wave functions, we predict that such a state is likely to occur when a system
of two-component bosons in two dimensions, interacting via a species
independent contact interaction, is exposed to a synthetic magnetic field of
strength that corresponds to a filling factor of unity. The fermions forming
the SU(2) singlet Fermi sea are bound states of bosons and quantized vortices,
formed as a result of the repulsive interaction between bosons in the lowest
Landau level
- …