27,350 research outputs found
GHZ-type and W-type entangled coherent states: generation and Bell-type inequality tests without photon counting
We study GHZ-type and W-type three-mode entangled coherent states. Both the
types of entangled coherent states violate Mermin's version of the Bell
inequality with threshold photon detection (i.e., without photon counting).
Such an experiment can be performed using linear optics elements and threshold
detectors with significant Bell violations for GHZ-type entangled coherent
states. However, to demonstrate Bell-type inequality violations for W-type
entangled coherent states, additional nonlinear interactions are needed. We
also propose an optical scheme to generate W-type entangled coherent states in
free-traveling optical fields. The required resources for the generation are a
single-photon source, a coherent state source, beam splitters, phase shifters,
photodetectors, and Kerr nonlinearities. Our scheme does not necessarily
require strong Kerr nonlinear interactions, i.e., weak nonlinearities can be
used for the generation of the W-type entangled coherent states. Furthermore,
it is also robust against inefficiencies of the single-photon source and the
photon detectors.Comment: 8 pages, 5 figures, to be published in Phys. Rev.
Classification of scale-free networks
While the emergence of a power law degree distribution in complex networks is
intriguing, the degree exponent is not universal. Here we show that the
betweenness centrality displays a power-law distribution with an exponent \eta
which is robust and use it to classify the scale-free networks. We have
observed two universality classes with \eta \approx 2.2(1) and 2.0,
respectively. Real world networks for the former are the protein interaction
networks, the metabolic networks for eukaryotes and bacteria, and the
co-authorship network, and those for the latter one are the Internet, the
world-wide web, and the metabolic networks for archaea. Distinct features of
the mass-distance relation, generic topology of geodesics and resilience under
attack of the two classes are identified. Various model networks also belong to
either of the two classes while their degree exponents are tunable.Comment: 6 Pages, 6 Figures, 1 tabl
Quantum states for perfectly secure secret sharing
In this work, we investigate what kinds of quantum states are feasible to
perform perfectly secure secret sharing, and present its necessary and
sufficient conditions. We also show that the states are bipartite distillable
for all bipartite splits, and hence the states could be distillable into the
Greenberger-Horne-Zeilinger state. We finally exhibit a class of secret-sharing
states, which have an arbitrarily small amount of bipartite distillable
entanglement for a certain split.Comment: 4 page
Optimal conversion of Bose condensed atoms into molecules via a Feshbach resonance
In many experiments involving conversion of quantum degenerate atomic gases
into molecular dimers via a Feshbach resonance, an external magnetic field is
linearly swept from above the resonance to below resonance. In the adiabatic
limit, the fraction of atoms converted into molecules is independent of the
functional form of the sweep and is predicted to be 100%. However, for
non-adiabatic sweeps through resonance, Landau-Zener theory predicts that a
linear sweep will result in a negligible production of molecules. Here we
employ a genetic algorithm to determine the functional time dependence of the
magnetic field that produces the maximum number of molecules for sweep times
that are comparable to the period of resonant atom-molecule oscillations,
. The optimal sweep through resonance indicates that
more than 95% of the atoms can be converted into molecules for sweep times as
short as while the linear sweep results in a
conversion of only a few percent. We also find that the qualitative form of the
optimal sweep is independent of the strength of the two-body interactions
between atoms and molecules and the width of the resonance
Recommended from our members
How Does Wind Project Performance Change with Age in the United States?
Wind-plant performance declines with age, and the rate of decline varies between regions. The rate of performance decline is important when determining wind-plant financial viability and expected lifetime generation. We determine the rate of age-related performance decline in the United States wind fleet by evaluating generation records from 917 plants. We find the rate of performance decline to be 0.53%/year for older vintages of plants and 0.17%/year for newer vintages of plants on an energy basis for the first 10 years of operation, which is on the lower end of prior estimates in Europe. Unique to the United States, we find a significant drop in performance by 3.6% after 10 years, as plants lose eligibility for the production tax credit. Certain plant characteristics, such as the ratio of blade length to nameplate capacity, influence the rate of performance decline. These results indicate that the performance decline rate can be partially managed and influenced by policy
- …