29,008 research outputs found
Non-destructive measurement of the transition probability in a Sr optical lattice clock
We present the experimental demonstration of non-destructive probing of the
1S0-3P0 clock transition probability in an optical lattice clock with 87Sr
atoms. It is based on the phase shift induced by the atoms on a weak
off-resonant laser beam. The method we propose is a differential measurement of
this phase shift on two modulation sidebands with opposite detuning with
respect to the 1S0-1P1 transition, allowing a detection limited by the photon
shot noise. We have measured an atomic population of 10^4 atoms with a signal
to noise ratio of 100 per cycle, while keeping more than 95% of the atoms in
the optical lattice with a depth of 0.1 mK. The method proves simple and robust
enough to be operated as part of the whole clock setup. This detection scheme
enables us to reuse atoms for subsequent clock state interrogations,
dramatically reducing the loading time and thereby improving the clock
frequency stability.Comment: 4 pages, 5 figure
Fractional Quantum Hall Effect in Topological Flat Bands with Chern Number Two
Recent theoretical works have demonstrated various robust Abelian and
non-Abelian fractional topological phases in lattice models with topological
flat bands carrying Chern number C=1. Here we study hard-core bosons and
interacting fermions in a three-band triangular-lattice model with the lowest
topological flat band of Chern number C=2. We find convincing numerical
evidence of bosonic fractional quantum Hall effect at the filling
characterized by three-fold quasi-degeneracy of ground states on a torus, a
fractional Chern number for each ground state, a robust spectrum gap, and a gap
in quasihole excitation spectrum. We also observe numerical evidence of a
robust fermionic fractional quantum Hall effect for spinless fermions at the
filling with short-range interactions.Comment: 5 pages, 7 figures, with Supplementary Materia
Luminous Infrared Galaxies in the Local Universe
We study the morphology and star formation properties of 159 local luminous
infrared galaxy (LIRG) using multi-color images from Data Release 2 (DR2) of
the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a
cross-correlation analysis between the IRAS survey and SDSS. They are all
brighter than 15.9 mag in the r-band and below redshift ~ 0.1, and so can be
reliably classified morphologically. We find that the fractions of
interacting/merging and spiral galaxies are ~ 48% and ~ 40% respectively. Our
results complement and confirm the decline (increase) in the fraction of spiral
(interacting/merging) galaxies from z ~1 to z ~ 0.1, as found by Melbourne, Koo
& Le Floc'h (2005). About 75% of spiral galaxies in the local LIRGs are barred,
indicating that bars may play an important role in triggering star formation
rates > 20 M_{sun}/yr in the local universe. Compared with high redshift LIRGs,
local LIRGs have lower specific star formation rates, smaller cold gas
fractions and a narrower range of stellar masses. Local LIRGs appear to be
either merging galaxies forming intermediate mass ellipticals or spiral
galaxies undergoing high star formation activities regulated by bars.Comment: 22 pages, 5 figures, accepted for publication in ApJ, title changed,
typos corrected,major revisions following referee's comments,updated
reference
Critical comments on the paper "Crossing by a single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu [Phys.Rev.D75,023510(2007)]
It is demonstrated that the claim in the paper "Crossing by a
single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu
[Phys.Rev.D75,023510(2007)], about a prove that there do not exist scaling
solutions in a universe with dust in a Dvali-Gabadadze-Porrati (DGP) braneworld
scenario, is incorrect.Comment: 5 pages, 8 eps figure
Heavy-tailed statistics in short-message communication
Short-message (SM) is one of the most frequently used communication channels
in the modern society. In this Brief Report, based on the SM communication
records provided by some volunteers, we investigate the statistics of SM
communication pattern, including the interevent time distributions between two
consecutive short messages and two conversations, and the distribution of
message number contained by a complete conversation. In the individual level,
the current empirical data raises a strong evidence that the human activity
pattern, exhibiting a heavy-tailed interevent time distribution, is driven by a
non-Poisson nature.Comment: 4 pages, 4 figures and 1 tabl
- …