1,005 research outputs found
Polarization and frequency disentanglement of photons via stochastic polarization mode dispersion
We investigate the quantum decoherence of frequency and polarization
variables of photons via polarization mode dispersion in optical fibers. By
observing the analogy between the propagation equation of the field and the
Schr\"odinger equation, we develop a master equation under Markovian
approximation and analytically solve for the field density matrix. We identify
distinct decay behaviors for the polarization and frequency variables for
single-photon and two-photon states. For the single photon case, purity
functions indicate that complete decoherence for each variable is possible only
for infinite fiber length. For entangled two-photon states passing through
separate fibers, entanglement associated with each variable can be completely
destroyed after characteristic finite propagation distances. In particular, we
show that frequency disentanglement is independent of the initial polarization
status. For propagation of two photons in a common fiber, the evolution of a
polarization singlet state is addressed. We show that while complete
polarization disentanglement occurs at a finite propagation distance, frequency
entanglement could survive at any finite distance for gaussian states.Comment: 2 figure
Low pH enhances the action of maximin H5 against Staphylococcus aureus and helps mediate lysylated phosphatidylglycerol induced resistance
Maximin H5 (MH5) is an amphibian antimicrobial peptide specifically targeting Staphylococcus aureus. At pH 6, the peptide showed an increased ability to penetrate (∆П = 6.2 mN m-1) and lyse (lysis = 48 %) S. aureus membrane mimics, which incorporated physiological levels of lysylated phosphatidylglycerol (Lys-PG, 60 %) as compared to pH 7 (∆П = 5.6 mN m-1 and lysis = 40 % at pH 7) where levels of Lys-PG are lower (40 %). The peptide therefore appears to have optimal function at pH levels known to be optimal for the organism’s growth. MH5 killed S. aureus (minimum inhibitory concentration = 90 µM) via membranolytic mechanisms that involved the stabilization of α-helical structure (circa 45-50 %) and which showed similarities to the ‘Carpet’ mechanism based on its ability to increase the rigidity (Cs-1 = 109.94 mN m-1) and thermodynamic stability (∆Gmix = -3.0) of physiologically relevant S. aureus membrane mimics at pH 6. Based on theoretical analysis this mechanism may involve the use of a tilted peptide structure and efficacy was noted to vary inversely with the Lys-PG content of S. aureus membrane mimics for each pH studied (R2 circa 0.97), which led to the suggestion that under biologically relevant conditions, low pH helps mediate Lys-PG induced resistance in S. aureus to MH5 antibacterial action. The peptide showed a lack of haemolytic activity (< 2 % haemolysis) and merits further investigation as a potential template for development as an anti-staphylococcal agent in medically and biotechnically relevant areas
Accumulation of entanglement in a continuous variable memory
We study the accumulation of entanglement in a memory device built out of two
continuous variable (CV) systems. We address the case of a qubit mediating an
indirect joint interaction between the CV systems. We show that, in striking
contrast with respect to registers built out of bidimensional Hilbert spaces,
entanglement superior to a single ebit can be efficiently accumulated in the
memory, even though no entangled resource is used. We study the protocol in an
immediately implementable setup, assessing the effects of the main
imperfections.Comment: 4 pages, 3 figures, RevTeX
Burst avalanches in solvable models of fibrous materials
We review limiting models for fracture in bundles of fibers, with
statistically distributed thresholds for breakdown of individual fibers. During
the breakdown process, avalanches consisting of simultaneous rupture of several
fibers occur, and the distribution of the magnitude of
such avalanches is the central characteristics in our analysis. For a bundle of
parallel fibers two limiting models of load sharing are studied and contrasted:
the global model in which the load carried by a bursting fiber is equally
distributed among the surviving members, and the local model in which the
nearest surviving neighbors take up the load. For the global model we
investigate in particular the conditions on the threshold distribution which
would lead to anomalous behavior, i.e. deviations from the asymptotics
, known to be the generic behavior. For the local
model no universal power-law asymptotics exists, but we show for a particular
threshold distribution how the avalanche distribution can nevertheless be
explicitly calculated in the large-bundle limit.Comment: 28 pages, RevTeX, 3 Postscript figure
Controlled order rearrangement encryption for quantum key distribution
A novel technique is devised to perform orthogonal state quantum key
distribution. In this scheme, entangled parts of a quantum information carrier
are sent from Alice to Bob through two quantum channels. However before the
transmission, the orders of the quantum information carrier in one channel is
reordered so that Eve can not steal useful information. At the receiver's end,
the order of the quantum information carrier is restored. The order
rearrangement operation in both parties is controlled by a prior shared control
key which is used repeatedly in a quantum key distribution session.Comment: 5 pages and 2 figure
Security against eavesdropping in quantum cryptography
In this article we deal with the security of the BB84 quantum cryptography
protocol over noisy channels using generalized privacy amplification. For this
we estimate the fraction of bits needed to be discarded during the privacy
amplification step. This estimate is given for two scenarios, both of which
assume the eavesdropper to access each of the signals independently and take
error correction into account. One scenario does not allow a delay of the
eavesdropper's measurement of a measurement probe until he receives additional
classical information. In this scenario we achieve a sharp bound. The other
scenario allows a measurement delay, so that the general attack of an
eavesdropper on individual signals is covered. This bound is not sharp but
allows a practical implementation of the protocol.Comment: 11 pages including 3 figures, contains new results not contained in
my Phys. Rev. A pape
Atom-photon entanglement generation and distribution
We extend an earlier model by Law {\it et al.} \cite{law} for a cavity QED
based single-photon-gun to atom-photon entanglement generation and
distribution. We illuminate the importance of a small critical atom number on
the fidelity of the proposed operation in the strong coupling limit. Our result
points to a promisingly high purity and efficiency using currently available
cavity QED parameters, and sheds new light on constructing quantum computing
and communication devices with trapped atoms and high Q optical cavities.Comment: 7 fig
Unambiguous Discrimination Between Linearly Dependent States with Multiple Copies
A set of quantum states can be unambiguously discriminated if and only if
they are linearly independent. However, for a linearly dependent set, if C
copies of the state are available, then the resulting C particle states may
form a linearly independent set, and be amenable to unambiguous discrimination.
We obtain necessary and sufficient conditions for the possibility of
unambiguous discrimination between N states given that C copies are available
and that the single copies span a D dimensional space. These conditions are
found to be identical for qubits. We then examine in detail the linearly
dependent trine ensemble. The set of C>1 copies of each state is a set of
linearly independent lifted trine states. The maximum unambiguous
discrimination probability is evaluated for all C>1 with equal a priori
probabilities.Comment: 12 Pages RevTeX 4, 1 EPS figur
Micro-channel–based high specific power lithium target
A micro-channel–based heat sink has been produced and tested. The device has been developed to be used as a Lithium target for the LENOS (Legnaro Neutron Source) facility and for the production of radioisotope. Nevertheless, applications of such device can span on many areas: cooling of electronic devices, diode laser array, automotive applications etc. The target has been tested using a proton beam of 2.8MeV energy and delivering total power shots from 100W to 1500W with beam spots varying from 5mm2 to 19mm2. Since the target has been designed to be used with a thin deposit of lithium and since lithium is a low-melting-point material, we have measured that, for such application, a specific power of about 3kW/cm2 can be delivered to the target, keeping the maximum surface temperature not exceeding 150◦C
Efficient quantum cryptography network without entanglement and quantum memory
An efficient quantum cryptography network protocol is proposed with
d-dimension polarized photons, without resorting to entanglement and quantum
memory. A server on the network, say Alice, provides the service for preparing
and measuring single photons whose initial state are |0>. The users code the
information on the single photons with some unitary operations. For preventing
the untrustworthy server Alice from eavesdropping the quantum lines, a
nonorthogonal-coding technique (decoy-photon technique) is used in the process
that the quantum signal is transmitted between the users. This protocol does
not require the servers and the users to store the quantum state and almost all
of the single photons can be used for carrying the information, which makes it
more convenient for application than others with present technology. We also
discuss the case with a faint laser pulse.Comment: 4 pages, 1 figures. It also presented a way for preparing decoy
photons without a sinigle-photon sourc
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