2,082 research outputs found
Quantum broadcast communication
Broadcast encryption allows the sender to securely distribute his/her secret
to a dynamically changing group of users over a broadcast channel. In this
paper, we just consider a simple broadcast communication task in quantum
scenario, which the central party broadcasts his secret to multi-receiver via
quantum channel. We present three quantum broadcast communication schemes. The
first scheme utilizes entanglement swapping and Greenberger-Horne-Zeilinger
state to realize a task that the central party broadcasts his secret to a group
of receivers who share a group key with him. In the second scheme, based on
dense coding, the central party broadcasts the secret to multi-receiver who
share each of their authentication key with him. The third scheme is a quantum
broadcast communication scheme with quantum encryption, which the central party
can broadcast the secret to any subset of the legal receivers
Nonlinear Decoherence in Quantum State Preparation of a Trapped Ion
We present a nonlinear decoherence model which models decoherence effect
caused by various decohereing sources in a quantum system through a nonlinear
coupling between the system and its environment, and apply it to investigating
decoherence in nonclassical motional states of a single trapped ion. We obtain
an exactly analytic solution of the model and find very good agreement with
experimental results for the population decay rate of a single trapped ion
observed in the NIST experiments by Meekhof and coworkers (D. M. Meekhof, {\it
et al.}, Phys. Rev. Lett. {\bf 76}, 1796 (1996)).Comment: 5 pages, Revte
Multiparty Quantum Secret Report
A multiparty quantum secret report scheme is proposed with quantum
encryption. The boss Alice and her agents first share a sequence of
(+1)-particle Greenberger--Horne--Zeilinger (GHZ) states that only Alice
knows which state each (+1)-particle quantum system is in. Each agent
exploits a controlled-not (CNot) gate to encrypt the travelling particle by
using the particle in the GHZ state as the control qubit. The boss Alice
decrypts the travelling particle with a CNot gate after performing a
operation on her particle in the GHZ state or not. After the GHZ states (the
quantum key) are used up, the parties check whether there is a vicious
eavesdropper, say Eve, monitoring the quantum line, by picking out some samples
from the GHZ states shared and measure them with two measuring bases. After
confirming the security of the quantum key, they use the GHZ states remained
repeatedly for next round of quantum communication. This scheme has the
advantage of high intrinsic efficiency for qubits and the total efficiency.Comment: 4 pages, no figure
Spin Star as Switch for Quantum Networks
Quantum state transfer is an important task in quantum information
processing. It is known that one can engineer the couplings of a
one-dimensional spin chain to achieve the goal of perfect state transfer. To
leverage the value of these spin chains, a spin star is potentially useful for
connecting different parts of a quantum network. In this work, we extend the
spin-chain engineering problem to the problems with a topology of a star
network. We show that a permanently coupled spin star can function as a network
switch for transferring quantum states selectively from one node to another by
varying the local potentials only. Together with one-dimensional chains, this
result allows applications of quantum state transfer be applied to more general
quantum networks.Comment: 10 pages, 2 figur
Quantum secure direct communication network with superdense coding and decoy photons
A quantum secure direct communication network scheme is proposed with quantum
superdense coding and decoy photons. The servers on a passive optical network
prepare and measure the quantum signal, i.e., a sequence of the -dimensional
Bell states. After confirming the security of the photons received from the
receiver, the sender codes his secret message on them directly. For preventing
a dishonest server from eavesdropping, some decoy photons prepared by measuring
one photon in the Bell states are used to replace some original photons. One of
the users on the network can communicate any other one. This scheme has the
advantage of high capacity, and it is more convenient than others as only a
sequence of photons is transmitted in quantum line.Comment: 6 pages, 2 figur
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
Demon-like Algorithmic Quantum Cooling and its Realization with Quantum Optics
The simulation of low-temperature properties of many-body systems remains one
of the major challenges in theoretical and experimental quantum information
science. We present, and demonstrate experimentally, a universal cooling method
which is applicable to any physical system that can be simulated by a quantum
computer. This method allows us to distill and eliminate hot components of
quantum states, i.e., a quantum Maxwell's demon. The experimental
implementation is realized with a quantum-optical network, and the results are
in full agreement with theoretical predictions (with fidelity higher than
0.978). These results open a new path for simulating low-temperature properties
of physical and chemical systems that are intractable with classical methods.Comment: 7 pages, 5 figures, plus supplementarity material
Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7
We report complex metamagnetic transitions in single crystals of the new low
carrier Kondo antiferromagnet YbRh3Si7. Electrical transport, magnetization,
and specific heat measurements reveal antiferromagnetic order at T_N = 7.5 K.
Neutron diffraction measurements show that the magnetic ground state of
YbRh3Si7 is a collinear antiferromagnet where the moments are aligned in the ab
plane. With such an ordered state, no metamagnetic transitions are expected
when a magnetic field is applied along the c axis. It is therefore surprising
that high field magnetization, torque, and resistivity measurements with H||c
reveal two metamagnetic transitions at mu_0H_1 = 6.7 T and mu_0H_2 = 21 T. When
the field is tilted away from the c axis, towards the ab plane, both
metamagnetic transitions are shifted to higher fields. The first metamagnetic
transition leads to an abrupt increase in the electrical resistivity, while the
second transition is accompanied by a dramatic reduction in the electrical
resistivity. Thus, the magnetic and electronic degrees of freedom in YbRh3Si7
are strongly coupled. We discuss the origin of the anomalous metamagnetism and
conclude that it is related to competition between crystal electric field
anisotropy and anisotropic exchange interactions.Comment: 23 pages and 4 figures in the main text. 7 pages and 5 figures in the
supplementary materia
Synthesis of Mesoporous Silica@CoâAl Layered Double Hydroxide Spheres: Layer-by-Layer Method and Their Effects on the Flame Retardancy of Epoxy Resins
Hierarchical mesoporous silica@CoâAl layered double hydroxide (m-SiO2@CoâAl LDH) spheres were prepared through a layer-by-layer assembly process, in order to integrate their excellent physical and chemical functionalities. TEM results depicted that, due to the electrostatic potential difference between m-SiO2 and CoâAl LDH, the synthetic m-SiO2@CoâAl LDH hybrids exhibited that m-SiO2 spheres were packaged by the CoâAl LDH nanosheets. Subsequently, the m-SiO2@CoâAl LDH spheres were incorporated into epoxy resin (EP) to prepare specimens for investigation of their flame-retardant performance. Cone results indicated that m-SiO2@CoâAl LDH incorporated obviously improved fire retardant of EP. A plausible mechanism of fire retardant was hypothesized based on the analyses of thermal conductivity, char residues, and pyrolysis fragments. Labyrinth effect of m-SiO2 and formation of graphitized carbon char catalyzed by CoâAl LDH play pivotal roles in the flame retardance enhancement
Characteristics of marine shipping emissions at berth: profiles for particulate matter and volatile organic compounds
Emissions from ships at berth play an important role regarding the exposure
of high density human populations to atmospheric pollutants in port areas;
however, these emissions are not well understood. In this study, volatile
organic compounds (VOCs) and particle emissions from 20 container ships at
berth were sampled and analyzed during the fuel switch period at Jingtang
Port in Hebei Province, China. VOCs and particles were analyzed using a gas
chromatography-mass spectrometer (GC-MS) and a single particle aerosol mass
spectrometer (SPAMS), respectively. VOC analysis showed that alkanes and
aromatics, especially benzene, toluene and heavier compounds e.g.,
n-heptane, n-octane and n-nonane, dominated the total identified
species. Secondary organic aerosol (SOA) yields and ozone (O3)
forming potential were
0.017âŻÂ±âŻ0.007âŻgâŻSOAâŻgâ1âŻVOCs and
2.63âŻÂ±âŻ0.37âŻgâŻO3âŻgâ1âŻVOCs, respectively. Both positive and
negative ion mass spectra from individual ships were derived and the
intensity of specific ions were quantified. Results showed that elemental
carbon (35.74âŻ%), elemental carbonâorganic carbon mixtures (33.95âŻ%)
and Na-rich particles (21.12âŻ%) were major classes, comprising 90.7âŻ%
of the particles observed. Particles from ship auxiliary engines were in the
0.2 to 2.5âŻÂ”m size range, with a peak occurring at around
0.4âŻÂ”m. The issue of using vanadium (V) as tracer element was
examined, and it was found that V was not a proper tracer of ship emissions
when using low sulfur content diesel oil. The average percentage of sulfate
particles observed in shipping emissions before and after switching to marine
diesel oil remained unchanged at 24âŻ%. Under certain wind conditions,
when berths were upwind of emission sources, the ratios before and after
1 January were 35 and 27âŻ% respectively. The impact of atmospheric
stability was discussed based on PM2.5 and primary pollutant (carbon
monoxide) concentration. With a background of frequent haze episodes and
complex mechanisms of particulate accumulation and secondary formation, the
impact of atmospheric stability is believed to have been weak on the sulfate
contribution from shipping emissions. The results from this study provide
robust support for port area air quality assessment and source apportionment.</p
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