3,549 research outputs found
Constraining the bulk Lorentz factor from the photosphere emission
We propose a direct and model-independent method to constrain the Lorentz
factor of a relativistically expanding object, like gamma-ray bursts. Only the
measurements, such as thermal component of the emission, the distance and the
variable time scale of the light curve, are used. If the uncertainties are
considered, we will obtain lower limits of the Lorentz factor instead. We apply
this method to GRB 090618 and get a lower limit of the Lorentz factor to be 22.
The method can be used to any relativistically moving object, such as gamma-ray
bursts, blazars, and soft gamma-ray repeaters, providing the thermal component
of the emission being observed.Comment: 10 pages, 1 figur
Supersolidity and phase diagram of softcore bosons in a triangular lattice
We study the softcore extended Bose Hubbard model in a two-dimensional
triangular lattice by using the quantum Monte Carlo methods. The ground state
phase diagram of the system exhibits a very fruitful structure. Except the Mott
insulating state, four kinds of solid states with respect to the commensurate
filling factors and are identified. Two of them (CDW II
and CDW III) are newly predicted. In incommensurate fillings, superfluid,
spuersolid as well as phase separation states are detected . As in the case for
the hardcore bosons, a supersolid phase exists in while it is
unstable towards the phase separation in . However, this instability
is refrained in due to the softening of the bosons and then a
supersolid phase survives.Comment: 4 pages, 5 figure
Static impurities in a supersolid of interacting hard-core bosons on a triangular lattice
We study the effect of impurities in a supersolid phase in comparison to the
behavior in the solid and superfluid phases. A supersolid phase has been
established for interacting hardcore bosons on a triangular lattice which may
be realizable by ultracold atomic gases. Static vacancies are considered in
this model which always lower the magnitude of the order parameter in the solid
or superfluid phases. In the supersolid phase, however, the impurities directly
affect both order parameters simultaneously and thereby reveal an interesting
interplay between them. In particular the solid order may be enhanced at the
cost of a strong reduction of the superfluidity, which shows that the two order
parameters cannot be in a simple superposition. We also observe an unusual
impurity pinning effect in the solid ordered phase, which results in two
distinct states separated by a first-order transition.Comment: 5 pages, 5 figures, final version. More information at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Criteria for two distinguishable fermions to behave like a boson
We study the necessary conditions for bosons composed of two distinguishable
fermions to exhibit bosonic-like behaviour. We base our analysis on tools of
quantum information theory such as entanglement and the majorization criterion
for probability distributions. In particular we scrutinize a recent interesting
hypothesis by C. K. Law in the Ref. Phys. Rev. A 71, 034306 (2005) that
suggests that the amount of entanglement between the constituent fermions is
related to the bosonic properties of the composite boson. We show that a large
amount of entanglement does not necessarily imply a good boson-like behaviour
by constructing an explicit counterexample. Moreover, we identify more
precisely the role entanglement may play in this situation.Comment: 6 pages, 1 figure (in color
Experimental detection of quantum coherent evolution through the violation of Leggett-Garg-type inequalities
We discuss the use of inequalities of the Leggett-Garg type (LGtI) to witness
quantum coherence and present the first experimental violation of this type of
inequalities using a light-matter interfaced system. By separately benchmarking
the Markovian character of the evolution and the translational invariance of
the conditional probabilities, the observed violation of a LGtI is attributed
to the quantum coherent character of the process. These results provide a
general method to benchmark `quantumness' when the absence of memory effects
can be independently certified and confirm the persistence of quantum coherent
features within systems of increasing complexity.Comment: published version, including supplementary materia
Correlation between Voronoi volumes in disc packings
We measure the two-point correlation of free Voronoi volumes in binary disc
packings, where the packing fraction ranges from 0.8175 to
0.8380. We observe short-ranged correlations over the whole range of and anti-correlations for . The spatial extent of
the anti-correlation increases with while the position of the
maximum of the anti-correlation and the extent of the positive correlation
shrink with . We conjecture that the onset of anti-correlation
corresponds to dilatancy onset in this system
How frequently does the stock price jump? \u2013 An analysis of high-frequency data with microstructure noises
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