12,816 research outputs found
Novel quantum phases of dipolar Bose gases in optical lattices
We investigate the quantum phases of polarized dipolar Bosons loaded into a
two-dimensional square and three-dimensional cubic optical lattices. We show
that the long-range and anisotropic nature of the dipole-dipole interaction
induces a rich variety of quantum phases, including the supersolid and striped
supersolid phases in 2D lattices, and the layered supersolid phase in 3D
lattices.Comment: 4 pages, 4 figure
From random walks to distances on unweighted graphs
Large unweighted directed graphs are commonly used to capture relations
between entities. A fundamental problem in the analysis of such networks is to
properly define the similarity or dissimilarity between any two vertices.
Despite the significance of this problem, statistical characterization of the
proposed metrics has been limited. We introduce and develop a class of
techniques for analyzing random walks on graphs using stochastic calculus.
Using these techniques we generalize results on the degeneracy of hitting times
and analyze a metric based on the Laplace transformed hitting time (LTHT). The
metric serves as a natural, provably well-behaved alternative to the expected
hitting time. We establish a general correspondence between hitting times of
the Brownian motion and analogous hitting times on the graph. We show that the
LTHT is consistent with respect to the underlying metric of a geometric graph,
preserves clustering tendency, and remains robust against random addition of
non-geometric edges. Tests on simulated and real-world data show that the LTHT
matches theoretical predictions and outperforms alternatives.Comment: To appear in NIPS 201
Using Simple Neural Networks to Correct Errors in Optical Data Transmission.
We have demonstrated the applicability of
neural-network-based systems to the problem
of reducing the effects of signal distortion,
and shown that such a system has the potential
to reduce the bit-error-rate in the digitized
version of the analogue electrical signal
derived from an optical data stream by a
substantial margin over existing techniques
Dipolar effect in coherent spin mixing of two atoms in a single optical lattice site
We show that atomic dipolar effects are detectable in the system that
recently demonstrated two-atom coherent spin dynamics within individual lattice
sites of a Mott state. Based on a two-state approximation for the two-atom
internal states and relying on a variational approach, we have estimated the
spin dipolar effect. Despite the absolute weakness of the dipole-dipole
interaction, it is shown that it leads to experimentally observable effects in
the spin mixing dynamics.Comment: 4 pages, 3 color eps figures, to appear in Phys. Rev. Let
New Interaction between Dark Energy and Dark Matter Changes Sign during Cosmological Evolution
It is found by Cai and Su that the interaction between dark energy and cold
dark matter is likely to change the sign during the cosmological evolution.
Motivated by this, we suggest a new form of interaction between dark energy and
dark matter, which changes from negative to positive as the expansion of our
universe changes from decelerated to accelerated. We find that the interacting
model is consistent with the second law of thermodynamics and the observational
constraints. And, we also discuss the unified adiabatic-squared sound speed of
the model.Comment: 16 pages, 3 figure, 1 table. Final version in PR
Making vortices in dipolar spinor condensates via rapid adiabatic passage
We propose to the create vortices in spin-1 condensates via magnetic
dipole-dipole interaction. Starting with a polarized condensate prepared under
large axial magnetic field, we show that by gradually inverting the field,
population transfer among different spin states can be realized in a controlled
manner. Under optimal condition, we generate a doubly quantized vortex state
containing nearly all atoms in the condensate. The resulting vortex state is a
direct manifestation of the dipole-dipole interaction and spin textures in
spinor condensates. We also point out that the whole process can be
qualitatively described by a simple rapid adiabatic passage model.Comment: 4 pages, 4 figure
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