1,210 research outputs found
Closed formula for the relative entropy of entanglement
The long-standing problem of finding a closed formula for the relative
entropy of entanglement (REE) for two qubits is addressed. A compact-form
solution to the inverse problem, which characterizes an entangled state for a
given closest separable state, is obtained. Analysis of the formula for a large
class of entangled states strongly suggests that a compact analytical solution
of the original problem, which corresponds to finding the closest separable
state for a given entangled state, can be given only in some special cases. A
few applications of the compact-form formula are given to show additivity of
the REE, to relate the REE with the Rains upper bound for distillable
entanglement, and to show that a Bell state does not have a unique closest
separable state.Comment: 7 pages, the title was modified as suggested by the PRA editor
Dilemma that cannot be resolved by biased quantum coin flipping
We show that a biased quantum coin flip (QCF) cannot provide the performance
of a black-boxed biased coin flip, if it satisfies some fidelity conditions.
Although such a QCF satisfies the security conditions of a biased coin flip, it
does not realize the ideal functionality, and therefore, does not fulfill the
demands for universally composable security. Moreover, through a comparison
within a small restricted bias range, we show that an arbitrary QCF is
distinguishable from a black-boxed coin flip unless it is unbiased on both
sides of parties against insensitive cheating. We also point out the difficulty
in developing cheat-sensitive quantum bit commitment in terms of the
uncomposability of a QCF.Comment: 5 pages and 1 figure. Accepted versio
Non-Thermal Emission from Relativistic Electrons in Clusters of Galaxies: A Merger Shock Acceleration Model
We have investigated evolution of non-thermal emission from relativistic
electrons accelerated at around the shock fronts during merger of clusters of
galaxies. We estimate synchrotron radio emission and inverse Compton scattering
of cosmic microwave background photons from extreme ultraviolet (EUV) to hard
X-ray range. The hard X-ray emission is most luminous in the later stage of
merger. Both hard X-ray and radio emissions are luminous only while signatures
of merging events are clearly seen in thermal intracluster medium (ICM). On the
other hand, EUV radiation is still luminous after the system has relaxed.
Propagation of shock waves and bulk-flow motion of ICM play crucial roles to
extend radio halos. In the contracting phase, radio halos are located at the
hot region of ICM, or between two substructures. In the expanding phase, on the
other hand, radio halos are located between two ICM hot regions and shows
rather diffuse distribution.Comment: 19 pages, 5 figures, accepted for publication in Ap
Use of a novel coaxial guide needle-wire (GNW) combination system for computed tomography guided radiofrequency tumor ablation
We developed a novel coaxial system using a fine guide needle wire (GNW) to safely and easily place the radiofrequency needle under CT-guidance. The GNW consists of a fine needle (diameter, 21-gauge; length, 150 mm) and a wire (0.018 inch, 250 mm). An exclusive radiofrequency cannula (14-gauge; 160 mm) was also used. This system was used for the treatment of six hepatocellular carcinomas in six patients. All lesions were located deeper than 10 cm from the needle entry site. This system was useful in performing CT-guided RF ablation for deeply or precariously located liver lesions particularly in patients who are unable to hold their breath
Two-Temperature Intracluster Medium in Merging Clusters of Galaxies
We investigate the evolution of intracluster medium during a cluster merger,
explicitly considering the relaxation process between the ions and electrons by
N-body and hydrodynamical simulations. When two subclusters collide each other,
a bow shock is formed between the centers of two substructures and propagate in
both directions along the collision axis. The shock primarily heats the ions
because the kinetic energy of an ion entering the shock is larger than that of
an electron by the ratio of masses. In the post-shock region the energy is
transported from the ions to electrons via Coulomb coupling. However, since the
energy exchange timescale depends both on the gas density and temperature,
distribution of electron temperature becomes more complex than that of the
plasma mean temperature, especially in the expanding phase. After the collision
of two subclusters, gas outflow occurs not only along the collision axis but
also in its perpendicular direction. The gas which is originally located in the
central part of the subclusters moves both in the parallel and perpendicular
directions. Since the equilibrium timescale of the gas along these directions
is relatively short, temperature difference between ions and electrons is
larger in the directions tilted by the angles of with respect to
the collision axis. The electron temperature could be significantly lower that
the plasma mean temperature by at most. The significance of our
results in the interpretation of X-ray observations is briefly discussed.Comment: 20 pages, 11 figures, Accepted for publication in Ap
Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system
We present a theoretical study of the relationship between entanglement and
entropy in multi-qubit quantum optical systems. Specifically we investigate
quantitative relations between the concurrence and linear entropy for a
two-qubit mixed system, implemented as two two-level atoms interacting with a
single-mode cavity field. The dynamical evolutions of the entanglement and
entropy, are controlled via time-dependent cavity-atom couplings. Our
theoretical findings lead us to propose an alternative measure of entanglement,
which could be used to develop a much needed correlation measure for more
general multi-partite quantum systems.Comment: New discussions on the generality of entanglement-entropy
relationship, one new reference, and other minor changes. 10 pages, 6
figures, accepted for publication in J.Opt. B: "Special Issue on Fluctuations
& Noise in Photonics & Quantum Optics.
Off-Center Mergers of Clusters of Galaxies and Nonequipartition of Electrons and Ions in Intracluster Medium
We investigate the dynamical evolution of clusters of galaxies and their
observational consequences during off-center mergers, explicitly considering
the relaxation process between ions and electrons in intracluster medium by
N-body and hydrodynamical simulations. In the contracting phase a bow shock is
formed between the two subclusters. The observed temperature between two peaks
in this phase depends on the viewing angle even if the geometry of the system
seems to be very simple like head-on collisions. Around the most contracting
epoch, when we observe merging clusters nearly along the collision axis, they
look like spherical relaxed clusters with large temperature gradients. In the
expanding phase, spiral bow shocks occur. As in head-on mergers, the electron
temperature is significantly lower than the plasma mean one especially in the
post-shock regions in the expanding phase. When the systems have relatively
large angular momentum, double-peak structures in the X-ray images can survive
even after the most contracting epoch. Morphological features in both X-ray
images and electron temperature distribution characteristic to off-center
mergers are seriously affected by the viewing angle. When the clusters are
observed nearly along the collision axis, the distribution of galaxies'
line-of-sight (LOS) velocities is a good indicator of mergers. In the
contracting phase, an negative kurtosis and a large skewness are expected for
nearly equal mass collisions and rather different mass ones, respectively. To
obtain statistically significant results, about 1000 galaxies' LOS velocities
are required. For nearby clusters (), large redshift surveys such as
2dF will enable us to study merger dynamics.Comment: 21 pages, 7 figures. Accepted for publication in Ap
Superconducting electronic state in optimally doped YBa2Cu3O7-d observed with laser-excited angle-resolved photoemission spectroscopy
Low energy electronic structure of optimally doped YBa2Cu3O7-d is
investigated using laser-excited angle-resolved photoemission spectroscopy. The
surface state and the CuO chain band that usually overlap the CuO2 plane
derived bands are not detected, thus enabling a clear observation of the bulk
superconducting state. The observed bilayer splitting of the Fermi surface is
~0.08 angstrom^{-1} along the (0,0)-(pi,pi) direction, significantly larger
than Bi2Sr2CaCu2O8+d. The kink structure of the band dispersion reflecting the
renormalization effect at ~60 meV shows up similarly as in other hole-doped
cuprates. The momentum-dependence of the superconducting gap shows
d_{x^2-y^2}-wave like amplitude, but exhibits a nonzero minimum of ~12 meV
along the (0,0)-(pi,pi) direction. Possible origins of such an unexpected
"nodeless" gap behavior are discussed.Comment: 9 pages, 10 figures; revised version accepted for publication in
Phys. Rev.
- âŠ