882 research outputs found
Quantum data hiding with spontaneous parameter down-conversion
Here we analyze the practical implication of the existing quantum data hiding
protocol with Bell states produced with optical downconverter. We show that the
uncertainty for the producing of the Bell states with spontaneous parameter
down-conversion should be taken into account, because it will cause serious
trouble to the hider encoding procedure. A set of extended Bell states and a
generalized Bell states analyzer are proposed to describe and analyze the
possible states of two photons distributing in two paths. Then we present a
method to integrate the above uncertainty of Bell states preparation into the
dating hiding procedure, when we encode the secret with the set of extended
Bell states. These modifications greatly simplify the hider's encoding
operations, and thus paves the way for the implementation of quantum data
hiding with present-day quantum optics.Comment: 4 pages, 1 figure, adding some analyse for security proof, to be
appear in Phys. Rev.
Chiral Extrapolation of Lattice Data for Heavy Baryons
The masses of heavy baryons containing a b quark have been calculated
numerically in lattice QCD with pion masses which are much larger than its
physical value. In the present work we extrapolate these lattice data to the
physical mass of the pion by applying the effective chiral Lagrangian for heavy
baryons, which is invariant under chiral symmetry when the light quark masses
go to zero and heavy quark symmetry when the heavy quark masses go to infinity.
A phenomenological functional form with three parameters, which has the correct
behavior in the chiral limit and appropriate behavior when the pion mass is
large, is proposed to extrapolate the lattice data. It is found that the
extrapolation deviates noticably from the naive linear extrapolation when the
pion mass is smaller than about 500MeV. The mass differences between Sigma_b
and Sigma_b^* and between Sigma_b^{(*)} and Lambda_b are also presented.
Uncertainties arising from both lattice data and our model parameters are
discussed in detail. We also give a comparision of the results in our model
with those obtained in the naive linear extrapolations.Comment: 29 pages, 9 figure
Controlled order rearrangement encryption for quantum key distribution
A novel technique is devised to perform orthogonal state quantum key
distribution. In this scheme, entangled parts of a quantum information carrier
are sent from Alice to Bob through two quantum channels. However before the
transmission, the orders of the quantum information carrier in one channel is
reordered so that Eve can not steal useful information. At the receiver's end,
the order of the quantum information carrier is restored. The order
rearrangement operation in both parties is controlled by a prior shared control
key which is used repeatedly in a quantum key distribution session.Comment: 5 pages and 2 figure
Collapse of ringlike structures in 2DEGs under tilted magnetic fields
In the quantum Hall regime, the longitudinal resistivity plotted
as a density--magnetic-field () diagram displays ringlike structures
due to the crossings of two sets of spin split Landau levels from different
subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801
(2005)]. For tilted magnetic fields, some of these ringlike structures "shrink"
as the tilt angle is increased and fully collapse at . Here we theoretically investigate the topology of these structures
via a non-interacting model for the 2DEG. We account for the inter Landau-level
coupling induced by the tilted magnetic field via perturbation theory. This
coupling results in anti-crossings of Landau levels with parallel spins. With
the new energy spectrum, we calculate the corresponding diagram of
the density of states (DOS) near the Fermi level. We argue that the DOS
displays the same topology as in the diagram. For the
ring with filling factor , we find that the anti-crossings make it
shrink for increasing tilt angles and collapse at a large enough angle. Using
effective parameters to fit the data, we find a collapsing
angle . Despite this factor-of-two discrepancy with
the experimental data, our model captures the essential mechanism underlying
the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in
August 2008 in Foz do Igua\c{c}u, Brazi
Energy transfer in a fast-slow Hamiltonian system
We consider a finite region of a lattice of weakly interacting geodesic flows
on manifolds of negative curvature and we show that, when rescaling the
interactions and the time appropriately, the energies of the flows evolve
according to a non linear diffusion equation. This is a first step toward the
derivation of macroscopic equations from a Hamiltonian microscopic dynamics in
the case of weakly coupled systems
Interoperability of different voltage source converter topologies in HVDC grids
This paper presents a detailed study of DC grid operation using a range of user-defined offline and real-time HVDC converter models which were rigorously validated against offline and real-time benchmarks. Provided that these models are destined for use in real-time hardware in the loop simulation and a wide range of offline system studies, this paper assesses their suitability for studying complex DC grids that consist of multiple voltage source converters which differ in their control range and fault ride-through capabilities. Detailed quantitative studies show that the offline and real-time DC grid models produce well matched results and provide efficient approaches to investigate DC grid operation during normal condition and AC and DC faults
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