1,569 research outputs found
Quantum circuit for security proof of quantum key distribution without encryption of error syndrome and noisy processing
One of the simplest security proofs of quantum key distribution is based on
the so-called complementarity scenario, which involves the complementarity
control of an actual protocol and a virtual protocol [M. Koashi, e-print
arXiv:0704.3661 (2007)]. The existing virtual protocol has a limitation in
classical postprocessing, i.e., the syndrome for the error-correction step has
to be encrypted. In this paper, we remove this limitation by constructing a
quantum circuit for the virtual protocol. Moreover, our circuit with a shield
system gives an intuitive proof of why adding noise to the sifted key increases
the bit error rate threshold in the general case in which one of the parties
does not possess a qubit. Thus, our circuit bridges the simple proof and the
use of wider classes of classical postprocessing.Comment: 8 pages, 2 figures. Typo correcte
Unconditionally secure key distillation from multi-photons
In this paper, we prove that the unconditionally secure key can be
surprisingly extracted from {\it multi}-photon emission part in the photon
polarization-based QKD. One example is shown by explicitly proving that one can
indeed generate an unconditionally secure key from Alice's two-photon emission
part in ``Quantum cryptography protocols robust against photon number splitting
attacks for weak laser pulses implementations'' proposed by V. Scarani {\it et
al.,} in Phys. Rev. Lett. {\bf 92}, 057901 (2004), which is called SARG04. This
protocol uses the same four states as in BB84 and differs only in the classical
post-processing protocol. It is, thus, interesting to see how the classical
post-processing of quantum key distribution might qualitatively change its
security. We also show that one can generate an unconditionally secure key from
the single to the four-photon part in a generalized SARG04 that uses six
states. Finally, we also compare the bit error rate threshold of these
protocols with the one in BB84 and the original six-state protocol assuming a
depolarizing channel.Comment: The title has changed again. We considerably improved our
presentation, and furthermore we proposed & analyzed a security of a modified
SARG04 protocol, which uses six state
Roles of the tensor and pairing correlations on the halo formation in 11Li
We study the roles of the tensor and pairing correlations on the halo
formation in 11Li with an extended 9Li+n+n model. We first solve the ground
state of 9Li in the shell model basis by taking 2p-2h states using the Gaussian
functions with variational size parameters to take into account the tensor
correlation fully. In 11Li, the tensor and pairing correlations in 9Li are
Pauli-blocked by additional two neutrons, which work coherently to make the
configurations containing the 0p1/2 state pushed up and close to those
containing the 1s1/2 state. Hence, the pairing interaction works efficiently to
mix the two configurations by equal amount and develop the halo structure in
11Li. For 10Li, the inversion phenomenon of s- and p-states is reproduced in
the same framework. Our model furthermore explains the recently observed
Coulomb breakup strength and charge radius for 11Li.Comment: 8 pages, 5 figure
Unconditionally Secure Key Distribution Based on Two Nonorthogonal States
We prove the unconditional security of the Bennett 1992 protocol, by using a
reduction to an entanglement distillation protocol initiated by a local
filtering process. The bit errors and the phase errors are correlated after the
filtering, and we can bound the amount of phase errors from the observed bit
errors by an estimation method involving nonorthogonal measurements. The angle
between the two states shows a trade-off between accuracy of the estimation and
robustness to noises.Comment: 5 pages, 1 figur
High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift
We present an analysis of a Suzaku observation of the link region between the
galaxy clusters A399 and A401. We obtained the metallicity of the intracluster
medium (ICM) up to the cluster virial radii for the first time. We determine
the metallicity where the virial radii of the two clusters cross each other (~2
Mpc away from their centers) and found that it is comparable to that in their
inner regions (~0.2 Zsun). It is unlikely that the uniformity of metallicity up
to the virial radii is due to mixing caused by a cluster collision. Since the
ram-pressure is too small to strip the interstellar medium of galaxies around
the virial radius of a cluster, the fairly high metallicity that we found there
indicates that the metals in the ICM are not transported from member galaxies
by ram-pressure stripping. Instead, the uniformity suggests that the
proto-cluster region was extensively polluted with metals by extremely powerful
outflows (superwinds) from galaxies before the clusters formed. We also
searched for the oxygen emission from the warm--hot intergalactic medium in
that region and obtained a strict upper limit of the hydrogen density
(nH<4.1x10^-5 cm^-3).Comment: Typo corrected. The published version is available on-line free of
charge by the end of 2008. http://pasj.asj.or.jp/v60/sp1/60s133/60s133.pd
On the performance of two protocols: SARG04 and BB84
We compare the performance of BB84 and SARG04, the later of which was
proposed by V. Scarani et al., in Phys. Rev. Lett. 92, 057901 (2004).
Specifically, in this paper, we investigate SARG04 with two-way classical
communications and SARG04 with decoy states. In the first part of the paper, we
show that SARG04 with two-way communications can tolerate a higher bit error
rate (19.4% for a one-photon source and 6.56% for a two-photon source) than
SARG04 with one-way communications (10.95% for a one-photon source and 2.71%
for a two-photon source). Also, the upper bounds on the bit error rate for
SARG04 with two-way communications are computed in a closed form by considering
an individual attack based on a general measurement. In the second part of the
paper, we propose employing the idea of decoy states in SARG04 to obtain
unconditional security even when realistic devices are used. We compare the
performance of SARG04 with decoy states and BB84 with decoy states. We find
that the optimal mean-photon number for SARG04 is higher than that of BB84 when
the bit error rate is small. Also, we observe that SARG04 does not achieve a
longer secure distance and a higher key generation rate than BB84, assuming a
typical experimental parameter set.Comment: 48 pages, 10 figures, 1 column, changed Figs. 7 and
Heat conduction induced by non-Gaussian athermal fluctuations
We study the properties of heat conduction induced by non-Gaussian noises
from athermal environments. We find that new terms should be added to the
conventional Fourier law and the fluctuation theorem for the heat current,
where its average and fluctuation are determined not only by the noise
intensities but also by the non-Gaussian nature of the noises. Our results
explicitly show the absence of the zeroth law of thermodynamics in athermal
systems.Comment: 15 pages, 4 figures, PRE in pres
Large-Scale Wind-Tunnel Tests and Evaluation of the Low-Speed Performance of a 35 deg Sweptback Wing Jet Transport Model Equipped with a Blowing Boundary-Layer-Control Flap and Leading-Edge Slat
A wind-tunnel investigation was conducted to determine the effect of trailing-edge flaps with blowing-type boundary-layer control and leading-edge slats on the low-speed performance of a large-scale jet transport model with four engines and a 35 deg. sweptback wing of aspect ratio 7. Two spanwise extents and several deflections of the trailing-edge flap were tested. Results were obtained with a normal leading-edge and with full-span leading-edge slats. Three-component longitudinal force and moment data and boundary-layer-control flow requirements are presented. The test results are analyzed in terms of possible improvements in low-speed performance. The effect on performance of the source of boundary-layer-control air flow is considered in the analysis
Unconditional security of the Bennett 1992 quantum key-distribution scheme with strong reference pulse
We prove the unconditional security of the original Bennett 1992 protocol
with strong reference pulse. We show that we may place a projection onto
suitably defined qubit spaces before the receiver, which makes the analysis as
simple as qubit-based protocols. Unlike the single-photon-based qubits, the
qubits identified in this scheme are almost surely detected by the receiver
even after a lossy channel. This leads to the key generation rate that is
proportional to the channel transmission rate for proper choices of
experimental parameters.Comment: More detailed presentation and a bit modified security proo
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