14,399 research outputs found
Characteristics of Bose-Einstein condensation in an optical lattice
We discuss several possible experimental signatures of the Bose-Einstein
condensation (BEC) transition for an ultracold Bose gas in an inhomogeneous
optical lattice. Based on the commonly used time-of-flight imaging technique,
we show that the momentum-space density profile in the first Brillouin zone,
supplemented by the visibility of interference patterns, provides valuable
information about the system. In particular, by crossing the BEC transition
temperature, the appearance of a clear bimodal structure sets a qualitative and
universal signature of this phase transition. Furthermore, the momentum
distribution can also be applied to extract the condensate fraction, which may
serve as a promising thermometer in such a system.Comment: 12 pages, 13 figures; Revised version with new figures; Phys. Rev. A
77, 043626 (2008
A scheme for demonstration of fractional statistics of anyons in an exactly solvable model
We propose a scheme to demonstrate fractional statistics of anyons in an
exactly solvable lattice model proposed by Kitaev that involves four-body
interactions. The required many-body ground state, as well as the anyon
excitations and their braiding operations, can be conveniently realized through
\textit{dynamic}laser manipulation of cold atoms in an optical lattice. Due to
the perfect localization of anyons in this model, we show that a quantum
circuit with only six qubits is enough for demonstration of the basic braiding
statistics of anyons. This opens up the immediate possibility of
proof-of-principle experiments with trapped ions, photons, or nuclear magnetic
resonance systems.Comment: 4 pages, 3 figure
Superfluid shells for trapped fermions with mass and population imbalance
We map out the phase diagram of strongly interacting fermions in a potential
trap with mass and population imbalance between the two spin components. As a
unique feature distinctively different from the equal-mass case, we show that
the superfluid here forms a shell structure which is not simply connected in
space. Different types of normal states occupy the trap regions inside and
outside this superfluid shell. We calculate the atomic density profiles, which
provide an experimental signature for the superfluid shell structure.Comment: 4 pages, 3 figure
Disclination in Lorentz Space-Time
The disclination in Lorentz space-time is studied in detail by means of
topological properties of -mapping. It is found the space-time
disclination can be described in term of a Dirac spinor. The size of the
disclination, which is proved to be the difference of two sets of su(2)% -like
monopoles expressed by two mixed spinors, is quantized topologically in terms
of topological invariantswinding number. The projection of space-time
disclination density along an antisymmetric tensor field is characterized by
Brouwer degree and Hopf index.Comment: Revtex, 7 page
Signal of Bose condensation in an optical lattice at finite temperature
We discuss the experimental signal for the Bose condensation of cold atoms in
an optical lattice at finite temperature. Instead of using the visibility of
the interference pattern via the time-of-flight imaging, we show that the
momentum space density profile in the first Brillouin zone, in particular its
bimodal distribution, provides an unambiguous signal for the Bose condensation.
We confirm this point with detailed calculation of the change in the atomic
momentum distribution across the condensation phase transition, taking into
account both the global trapping potential and the atomic interaction effects.Comment: 4 pages, 2 figures, replaced with the published versio
On the Applicability of Temperature and Precipitation Data from CMIP3 for China
Global Circulation Models (GCMs) contributed to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) and are widely used in global change research. This paper assesses the performance of the AR4 GCMs in simulating precipitation and temperature in China from 1960 to 1999 by comparison with observed data, using system bias (B), root-mean-square error (RMSE), Pearson correlation coefficient (R) and Nash-Sutcliffe model efficiency (E) metrics. Probability density functions (PDFs) are also fitted to the outputs of each model. It is shown that the performance of each GCM varies to different degrees across China. Based on the skill score derived from the four metrics, it is suggested that GCM 15 (ipsl_cm4) and GCM 3 (cccma_cgcm_t63) provide the best representations of temperature and precipitation, respectively, in terms of spatial distribution and trend over 10 years. The results also indicate that users should apply carefully the results of annual precipitation and annual temperature generated by AR4 GCMs in China due to poor performance. At a finer scale, the four metrics are also used to obtain best fit scores for ten river basins covering mainland China. Further research is proposed to improve the simulation accuracy of the AR4 GCMs regarding China
Correlations in interference and diffraction
Quantum formalism of Fraunhofer diffraction is obtained. The state of the
diffraction optical field is connected with the state of the incident optical
field by a diffraction factor. Based on this formalism, correlations of the
diffraction modes are calculated with different kinds of incident optical
fields. Influence of correlations of the incident modes on the diffraction
pattern is analyzed and an explanation of the ''ghost'' diffraction is
proposed.Comment: 16 pages, 2 figures, Latex, to appear in J. Mod. Op
Simulation and detection of Dirac fermions with cold atoms in an optical lattice
We propose an experimental scheme to simulate and observe relativistic Dirac
fermions with cold atoms in a hexagonal optical lattice. By controlling the
lattice anisotropy, one can realize both massive and massless Dirac fermions
and observe the phase transition between them. Through explicit calculations,
we show that both the Bragg spectroscopy and the atomic density profile in a
trap can be used to demonstrate the Dirac fermions and the associated phase
transition.Comment: 4 pages; Published versio
Temperature driven structural phase transition for trapped ions and its experimental detection
A Wigner crystal formed with trapped ion can undergo structural phase
transition, which is determined only by the mechanical conditions on a
classical level. Instead of this classical result, we show that through
consideration of quantum and thermal fluctuation, a structural phase transition
can be solely driven by change of the system's temperature. We determine a
finite-temperature phase diagram for trapped ions using the renormalization
group method and the path integral formalism, and propose an experimental
scheme to observe the predicted temperature-driven structural phase transition,
which is well within the reach of the current ion trap technology.Comment: 4 pages, 5 figure
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