13,004 research outputs found
Modelling Time-varying Dark Energy with Constraints from Latest Observations
We introduce a set of two-parameter models for the dark energy equation of
state (EOS) to investigate time-varying dark energy. The models are
classified into two types according to their boundary behaviors at the redshift
and their local extremum properties. A joint analysis based on
four observations (SNe + BAO + CMB + ) is carried out to constrain all the
models. It is shown that all models get almost the same and the cosmological parameters with the
best-fit results , although the constraint results on two
parameters and the allowed regions for the EOS are
sensitive to different models and a given extra model parameter. For three of
Type I models which have similar functional behaviors with the so-called CPL
model, the constrained two parameters and have negative correlation
and are compatible with the ones in CPL model, and the allowed regions of
get a narrow node at . The best-fit results from the most
stringent constraints in Model Ia give which may compare with the best-fit results in the CPL model. For four of
Type II models which have logarithmic function forms and an extremum point, the
allowed regions of are found to be sensitive to different models and a
given extra parameter. It is interesting to obtain two models in which two
parameters and are strongly correlative and appropriately reduced
to one parameter by a linear relation .Comment: 30 pages, 7 figure
Uncertainty relation in Schwarzschild spacetime
We explore the entropic uncertainty relation in the curved background outside
a Schwarzschild black hole, and find that Hawking radiation introduces a
nontrivial modification on the uncertainty bound for particular observer,
therefore it could be witnessed by proper uncertainty game experimentally. We
first investigate an uncertainty game between a free falling observer and his
static partner holding a quantum memory initially entangled with the quantum
system to be measured. Due to the information loss from Hawking decoherence, we
find an inevitable increase of the uncertainty on the outcome of measurements
in the view of static observer, which is dependent on the mass of the black
hole, the distance of observer from event horizon, and the mode frequency of
quantum memory. To illustrate the generality of this paradigm, we relate the
entropic uncertainty bound with other uncertainty probe, e.g., time-energy
uncertainty. In an alternative game between two static players, we show that
quantum information of qubit can be transferred to quantum memory through a
bath of fluctuating quantum fields outside the black hole. For a particular
choice of initial state, we show that the Hawking decoherence cannot counteract
entanglement generation after the dynamical evolution of system, which triggers
an effectively reduced uncertainty bound that violates the intrinsic limit
. Numerically estimation for a proper choice of initial state shows
that our result is comparable with possible real experiments. Finally, a
discussion on the black hole firewall paradox in the context of entropic
uncertainty relation is given.Comment: 11 pages, 2figures. Minor typos corrected, references and comment on
the black hole firewall added. Matches the version to appear in Physics
Letters
Exact two-qubit universal quantum circuit
We provide an analytic way to implement any arbitrary two-qubit unitary
operation, given an entangling two-qubit gate together with local gates. This
is shown to provide explicit construction of a universal quantum circuit that
exactly simulates arbitrary two-qubit operations in SU(4). Each block in this
circuit is given in a closed form solution. We also provide a uniform upper
bound of the applications of the given entangling gates, and find that exactly
half of all the Controlled-Unitary gates satisfy the same upper bound as the
CNOT gate. These results allow for the efficient implementation of operations
in SU(4) required for both quantum computation and quantum simulation.Comment: 5 page
Interaction of Copper-Amine With Southern Pine: Retention and Migration
The retention and leachability of copper in copper-amine (Cu-EA)-treated southern pine (SP) are influenced by the formulation and the composition of copper-amine treating solutions. The sources of copper used, Cu(OH)2, CuCO3, CuSO4, and Cu(NO3)2, in the copper-amine complex formulation affect the leachability of copper. Data show that copper-amine from CuSO4- and Cu(NO3)2-treated wood has less copper loss during laboratory water leaching than that from Cu(OH)2- and CuCO3-treated wood. Increasing the amine-to-copper molar ratio increases the copper retention by wood, but reduces the leach resistance of copper. The nature of amine ligands, such as monoethanolamine (primary amine), 2-methylamino-ethanol (secondary amine), and N, N-dimethyl-ethanolamine (tertiary amine), has some effect on copper retention and copper leaching. As the molecular weight of amine ligands increases, copper loss during leaching decreases
Dynamics of a deformable body in a fast flowing soap film
We study the behavior of an elastic loop embedded in a flowing soap film.
This deformable loop is wetted into the film and is held fixed at a single
point against the oncoming flow. We interpret this system as a two-dimensional
flexible body interacting in a two-dimensional flow. This coupled
fluid-structure system shows bistability, with both stationary and oscillatory
states. In its stationary state, the loop remains essentially motionless and
its wake is a von K\'arm\'an vortex street. In its oscillatory state, the loop
sheds two vortex dipoles, or more complicated vortical structures, within each
oscillation period. We find that the oscillation frequency of the loop is
linearly proportional to the flow velocity, and that the measured Strouhal
numbers can be separated based on wake structure
Variational Monte Carlo study of chiral spin liquid in the extended Heisenberg model on the Kagome lattice
We investigate the extended Heisenberg model on the Kagome lattice by using
Gutzwiller projected fermionic states and the variational Monte Carlo
technique. In particular, when both second- and third-neighbor super-exchanges
are considered, we find that a gapped spin liquid described by non-trivial
magnetic fluxes and long-range chiral-chiral correlations is energetically
favored compared to the gapless U(1) Dirac state. Furthermore, the topological
Chern number, obtained by integrating the Berry curvature, and the degeneracy
of the ground state, by constructing linearly independent states, lead us to
identify this flux state as the chiral spin liquid with fractionalized
Chern number.Comment: 9 pages, 7 figure
Multiparty Quantum Secret Sharing Based on Entanglement Swapping
A multiparty quantum secret sharing (QSS) protocol is proposed by using
swapping quantum entanglement of Bell states. The secret messages are imposed
on Bell states by local unitary operations. The secret messages are split into
several parts and each part is distributed to a party so that no action of a
subset of all the parties but their entire cooperation is able to read out the
secret messages. In addition, the dense coding is used in this protocol to
achieve a high efficiency. The security of the present multiparty QSS against
eavesdropping has been analyzed and confirmed even in a noisy quantum channel.Comment: 5 page
Optimal quantum circuit synthesis from Controlled-U gates
From a geometric approach, we derive the minimum number of applications
needed for an arbitrary Controlled-Unitary gate to construct a universal
quantum circuit. A new analytic construction procedure is presented and shown
to be either optimal or close to optimal. This result can be extended to
improve the efficiency of universal quantum circuit construction from any
entangling gate. Specifically, for both the Controlled-NOT and Double-CNOT
gates, we develop simple analytic ways to construct universal quantum circuits
with three applications, which is the least possible.Comment: 4 pages, 3 figure
Dilaton Black Holes in de Sitter or Anti-de Sitter Universe
Poletti and Wiltshire have shown that, with the exception of a pure
cosmological constant, the solution of a dilaton black hole in the background
of de Sitter or anti-de Sitter universe, does not exist in the presence of one
Liouville-type dilaton potential. Here with the combination of three
Liouville-type dilaton potentials, we obtain the dilaton black hole solutions
in the background of de Sitter or anti-de Sitter universe.Comment: 13 pages,to appear in Phys. Rev.
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