2,848 research outputs found
Efficient-phase-encoding protocols for continuous-variable quantum key distribution using coherent states and postselection
We propose efficient-phase-encoding protocols for continuous-variable quantum
key distribution using coherent states and postselection. By these phase
encodings, the probability of basis mismatch is reduced and total efficiency is
increased. We also propose mixed-state protocols by omitting a part of
classical communication steps in the efficient-phase-encoding protocols. The
omission implies a reduction of information to an eavesdropper and possibly
enhances the security of the protocols. We investigate the security of the
protocols against individual beam splitting attack.Comment: RevTeX4, 8 pages, 9 figure
Modeling Grain Boundaries using a Phase Field Technique
We propose a two dimensional frame-invariant phase field model of grain
impingement and coarsening. One dimensional analytical solutions for a stable
grain boundary in a bicrystal are obtained, and equilibrium energies are
computed. We are able to calculate the rotation rate for a free grain between
two grains of fixed orientation. For a particular choice of functional
dependencies in the model the grain boundary energy takes the same analytic
form as the microscopic (dislocation) model of Read and Shockley.Comment: 4 pages, 2 figure
The effect of supersymmetry breaking in the Mass Varying Neutrinos
We discuss the effect of the supersymmetry breaking on the Mass Varying
Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the
gravitational interaction between the hidden sector and the dark energy sector
is studied. A model including a chiral superfield in the dark sector and the
right handed neutrino superfield is proposed. Evolutions of the neutrino mass
and the equation of state parameter are presented in the model. It is remarked
that only the mass of a sterile neutrino is variable in the case of the
vanishing mixing between the left-handed and a sterile neutrino on cosmological
time scale. The finite mixing makes the mass of the left-handed neutrino
variable.Comment: 6 pages, 7 figures, RevTeX4, references added, discussions and
figures revise
Probing the Structure of Gamma-Ray Burst Jets with Steep Decay Phase of their Early X-ray Afterglows
We show that the jet structure of gamma-ray bursts (GRBs) can be investigated
with the tail emission of the prompt GRB. The tail emission which we consider
is identified as a steep-decay component of the early X-ray afterglow observed
by the X-ray Telescope onboard Swift. Using a Monte Carlo method, we derive,
for the first time, the distribution of the decay index of the GRB tail
emission for various jet models. The new definitions of the zero of time and
the time interval of a fitting region are proposed. These definitions for
fitting the light curve lead us an unique definition of the decay index, which
is useful to investigate the structure of the GRB jet. We find that if the GRB
jet has a core-envelope structure, the predicted distribution of the decay
index of the tail has a wide scatter and has multiple peaks, which cannot be
seen for the case of the uniform and the Gaussian jet. Therefore, the decay
index distribution tells us the information on the jet structure. Especially,
if we observe events whose decay index is less than about 2, both the uniform
and the Gaussian jet models will be disfavored according to our simulation
study.Comment: 21 pages, 10 figures, the paper with full resolution images is
http://theo.phys.sci.hiroshima-u.ac.jp/~takami/research/achievements/papers/003_full.pd
Exciton Mott transition in Si Revealed by Terahertz Spectroscopy
Exciton Mott transition in Si is investigated by using terahertz time-domain
spectroscopy. The excitonic correlation as manifested by the 1s-2p resonance is
observed above the Mott density. The scattering rate of charge carriers is
prominently enhanced at the proximity of Mott density, which is attributed to
the non-vanishing exciton correlation in the metallic electron-hole plasma.
Concomitantly, the signature of plasmon-exciton coupling is observed in the
loss function spectra.Comment: 5 pages, 3 figure
Analysis of an experimental quantum logic gate by complementary classical operations
Quantum logic gates can perform calculations much more efficiently than their
classical counterparts. However, the level of control needed to obtain a
reliable quantum operation is correspondingly higher. In order to evaluate the
performance of experimental quantum gates, it is therefore necessary to
identify the essential features that indicate quantum coherent operation. In
this paper, we show that an efficient characterization of an experimental
device can be obtained by investigating the classical logic operations on a
pair of complementary basis sets. It is then possible to obtain reliable
predictions about the quantum coherent operations of the gate such as
entanglement generation and Bell state discrimination even without performing
these operations directly.Comment: 14 pages, 1 figure, 3 tables, Brief Review for Modern Physics Letters
A, includes a more detailed analysis of the experimental data in Phys. Rev.
Lett. 95, 210506 (2005) (quant-ph/0506263). v2 has minor corrections in
layou
Fidelity criterion for quantum-domain transmission and storage of coherent states beyond unit-gain constraint
We generalize the experimental success criterion for quantum
teleportation/memory in continuous-variable quantum systems to be suitable for
non-unit-gain condition by considering attenuation/amplification of the
coherent-state amplitude. The new criterion can be used for a non-ideal quantum
memory and long distance quantum communication as well as quantum devices with
amplification process. It is also shown that the framework to measure the
average fidelity is capable of detecting all Gaussian channels in quantum
domain.Comment: 4pages, No figures, Accepted for publication in PR
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