7,457 research outputs found
Remote Preparation of Mixed States via Noisy Entanglement
We present a practical and general scheme of remote preparation for pure and
mixed state, in which an auxiliary qubit and controlled-NOT gate are used. We
discuss the remote state preparation (RSP) in two important types of decoherent
channel (depolarizing and dephaseing). In our experiment, we realize RSP in the
dephaseing channel by using spontaneous parametric down conversion (SPDC),
linear optical elements and single photon detector.Comment: 10 pages, 5 figures, submitted to PR
Probing the tidal disruption flares of massive black holes with high-energy neutrinos
The recently discovered high-energy transient Swift J164449.3+573451 (Sw
J1644+57) is thought to arise from the tidal disruption of a passing star by a
dormant massive black hole. Modeling of the broadband emission suggests the
presence of a powerful relativistic jet, which contributes dominantly to the
observed X-ray emission. Here we suggest that protons can be accelerated to
ultra-high energies by internal shocks occurring in the jets, but their flux is
insufficient to account for the observed flux of ultra-high energy cosmic rays.
High energy protons can produce ~0.1-10 PeV neutrinos through photomeson
interactions with X-ray photons. The large X-ray fluence (7x10^-4 erg cm^-2)
and high photopion efficiency, together with the insignificant cooling of
secondary mesons, result in bright neutrino emission expected from Sw J1644+57
if the jet composition is matter-dominated. One to several neutrinos may be
detected by a Km^3-scale detector from one tidal disruption event similar to Sw
J1644+57, thereby providing a powerful probe of the composition of the jets.Comment: 5 pages, 2 figures, accepted for publication as a Rapid Communication
in Physical Review D, abstract slightly extende
Varying the forcing scale in low Prandtl number dynamos
Small-scale dynamos are expected to operate in all astrophysical fluids that
are turbulent and electrically conducting, for example the interstellar medium,
stellar interiors, and accretion disks, where they may also be affected by or
competing with large-scale dynamos. However, the possibility of small-scale
dynamos being excited at small and intermediate ratios of viscosity to magnetic
diffusivity (the magnetic Prandtl number) has been debated, and the possibility
of them depending on the large-scale forcing wavenumber has been raised. Here
we show, using four values of the forcing wavenumber, that the small-scale
dynamo does not depend on the scale-separation between the size of the
simulation domain and the integral scale of the turbulence, i.e., the forcing
scale. Moreover, the spectral bottleneck in turbulence, which has been implied
as being responsible for raising the excitation conditions of small-scale
dynamos, is found to be invariant under changing the forcing wavenumber.
However, when forcing at the lowest few wavenumbers, the effective forcing
wavenumber that enters in the definition of the magnetic Reynolds number is
found to be about twice the minimum wavenumber of the domain. Our work is
relevant to future studies of small-scale dynamos, of which several
applications are being discussed.Comment: 8 pages, 5 figures, MNRAS, resubmitte
Information loss in local dissipation environments
The sensitivity of entanglement to the thermal and squeezed reservoirs'
parameters is investigated regarding entanglement decay and what is called
sudden-death of entanglement, ESD, for a system of two qubit pairs. The
dynamics of information is investigated by means of the information disturbance
and exchange information. We show that for squeezed reservoir, we can keep both
of the entanglement and information survival for a long time. The sudden death
of information is seen in the case of thermal reservoir
A Unified Quantum NOT Gate
We study the feasibility of implementing a quantum NOT gate (approximate)
when the quantum state lies between two latitudes on the Bloch's sphere and
present an analytical formula for the optimized 1-to- quantum NOT gate. Our
result generalizes previous results concerning quantum NOT gate for a quantum
state distributed uniformly on the whole Bloch sphere as well as the phase
covariant quantum state. We have also shown that such 1-to- optimized NOT
gate can be implemented using a sequential generation scheme via matrix product
states (MPS)
Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at z=0.194: the Central Excess Iron and SN Ia Enrichment
We present the Chandra study of the intermediately distant cluster of
galaxies MS 0839.9+2938. By performing both the projected and deprojected
spectral analyses, we find that the gas temperature is approximately constant
at about 4 keV in 130-444h_70^-1 kpc. In the inner regions, the gas temperature
descends towards the center, reaching <~ 3 keV in the central 37h_70^-1 kpc.
This infers that the lower and upper limits of the mass deposit rate are 9-34
M_sun yr^-1 and 96-126 M_sun yr^-1, respectively within 74h_70^-1 kpc where the
gas is significantly colder. Along with the temperature drop, we detect a
significant inward iron abundance increase from about 0.4 solar in the outer
regions to about 1 solar within the central 37h_70^-1 kpc. Thus MS 0839.9+2938
is the cluster showing the most significant central iron excess at z>~ 0.2. We
argue that most of the excess iron should have been contributed by SNe Ia. By
utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that
the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr,
which is similar to those found for the nearby clusters. Coinciding with the
optical extension of the cD galaxy (up to about 30h_70^-1 kpc), the observed
X-ray surface brightness profile exhibits an excess beyond the distribution
expected by either the beta model or the NFW model, and can be well fitted with
an empirical two-beta model that leads to a relatively flatter mass profile in
the innermost region.Comment: Accepted for publication in Ap
Low energy physical properties of high-Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments
In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed
out that an early resonating valence bond (RVB) theory is able to explain a
number of unusual properties of high temperature superconducting (SC)
Cu-oxides. Here we extend previous calculations \cite{anderson87,FC
Zhang,Randeria} to study more systematically low energy physical properties of
the plain vanilla d-wave RVB state, and to compare results with the available
experiments. We use a renormalized mean field theory combined with variational
Monte Carlo and power Lanczos methods to study the RVB state of an extended
model in a square lattice with parameters suitable for the hole doped
Cu-oxides. The physical observable quantities we study include the specific
heat, the linear residual thermal conductivity, the in-plane magnetic
penetration depth, the quasiparticle energy at the antinode , the
superconducting energy gap, the quasiparticle spectra and the Drude weight. The
traits of nodes (including , the Fermi velocity and the velocity
along Fermi surface ), as well as the SC order parameter are also
studied. Comparisons of the theory and the experiments in cuprates show an
overall qualitative agreement, especially on their doping dependences.Comment: 12 pages, 14 figures, 1 tabl
Scale-free download network for publications
The scale-free power-law behavior of the statistics of the download frequency
of publications has been, for the first time, reported. The data of the
download frequency of publications are taken from a well-constructed web page
in the field of economic physics (http://www.unifr.ch/econophysics/). The
Zipf-law analysis and the Tsallis entropy method were used to fit the download
frequency. It was found that the power-law exponent of rank-ordered frequency
distribution is which is consistent with the
power-law exponent for the cumulated frequency
distributions. Preferential attachment model of Barabasi and Albert network has
been used to explain the download network.Comment: 3 pages, 2 figure
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