9,256 research outputs found
The effects of optically induced non-Abelian gauge field in cold atoms
We show that degenerate dark states can be generated by coupling
-fold degenerate ground states and a common excited state with laser
fields. Interferences between light waves with different frequencies can
produce laser fields with time-dependent amplitudes, which can induce not only
U(N) non-Abelian vector fields but also the scalar ones for the adiabatic
motion of atoms in such laser fields. As an example, a time-periodic gauge
potential is produced by applying specific laser fields to a tripod system.
Some features of the Landau levels and the ground-state phase diagram of a
rotating Bose-Einstein condensate for a concrete gauge field are also
discussed.Comment: Revtex 6 pages, 2 figures, version to be published in PR
Vertex-Coloring 2-Edge-Weighting of Graphs
A -{\it edge-weighting} of a graph is an assignment of an integer
weight, , to each edge . An edge weighting naturally
induces a vertex coloring by defining for every
. A -edge-weighting of a graph is \emph{vertex-coloring} if
the induced coloring is proper, i.e., for any edge .
Given a graph and a vertex coloring , does there exist an
edge-weighting such that the induced vertex coloring is ? We investigate
this problem by considering edge-weightings defined on an abelian group.
It was proved that every 3-colorable graph admits a vertex-coloring
-edge-weighting \cite{KLT}. Does every 2-colorable graph (i.e., bipartite
graphs) admit a vertex-coloring 2-edge-weighting? We obtain several simple
sufficient conditions for graphs to be vertex-coloring 2-edge-weighting. In
particular, we show that 3-connected bipartite graphs admit vertex-coloring
2-edge-weighting
Two-copy Quantum Teleportation
We investigate two-copy scenario of quantum teleportation based on Bell
measurements. The detailed protocol is presented and the general expression of
the corresponding optimal teleportation delity is derived, which is given by
the two-copy fully entangled fraction that is invariant under local unitary
transformations. We prove that under a speci c case of the protocol, which is
signi cant for improving the optimal delity, the set of states with their
two-copy fully entangled fractions bounded by a threshold value that required
for useful two-copy teleportation is convex and compact. Hence the witness
operators exist to separate states that are useful for two-copy teleportation
from the rest ones. Moreover, we show that the optimal delity of two-copy
teleportation surpasses that of the original one copy teleportation.Comment: 8 pages, 2 figure
Conversion of K-Rb mixtures into stable molecules
We study the conversion of K and Rb atoms into stable molecules
through the stimulated Raman adiabatic passage (STIRAP) in photoassociation
assisted with Feshbach resonance. Starting with the mean-field Langrange
density, we show that the atom-to-molecule conversion efficiency by STIRAP
aided by Feshbach resonance is much larger than that by bare Feshbach
resonance. We also study the influence of the population imbalance on the
atom-to-molecule conversion.Comment: Revtex, 5 pages, 3 figures; version to appear in PRA (some content
changed
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