192 research outputs found
Simulation in inventory management
In this paper inventory management is analyzed as an organic part of the supply chain managing process. In today’s competitive economic environment traditional inventory policies should be improved. Simulation models enable a priori managing and analyzing variety of possible results and implication of selected inventory policies. The model presented in this paper uses the Monte Carlo simulation method and variables taken as random, in order to depict a harmonization and integration of dynamic quantitative analysis and theoretical, qualitative concepts of inventory management.Monte Carlo simulation, modeling, inventory management, supply chain management., Research and Development/Tech Change/Emerging Technologies, C15, C63,
Four-photon correction in two-photon Bell experiments
Correlated photons produced by spontaneous parametric down-conversion are an
essential tool for quantum communication, especially suited for long-distance
connections. To have a reasonable count rate after all the losses in the
propagation and the filters needed to improve the coherence, it is convenient
to increase the intensity of the laser that pumps the non-linear crystal. By
doing so, however, the importance of the four-photon component of the
down-converted field increases, thus degrading the quality of two-photon
interferences. In this paper, we present an easy derivation of this nuisance
valid for any form of entanglement generated by down-conversion, followed by a
full study of the problem for time-bin entanglement. We find that the
visibility of two-photon interferences decreases as V=1-2\rho, where \rho is,
in usual situations, the probability per pulse of creating a detectable photon
pair. In particular, the decrease of V is independent of the coherence of the
four-photon term. Thanks to the fact that \rho can be measured independently of
V, the experimental verification of our prediction is provided for two
different configuration of filters.Comment: 16 pages, 4 figures; published versio
Creating high dimensional time-bin entanglement using mode-locked lasers
We present a new scheme to generate high dimensional entanglement between two
photonic systems. The idea is based on parametric down conversion with a
sequence of pump pulses generated by a mode-locked laser. We prove
experimentally the feasibility of this scheme by performing a Franson-type Bell
test using a 2-way interferometer with path-length difference equal to the
distance between 2 pump pulses. With this experiment, we can demonstrate
entanglement for a two-photon state of at least dimension D=11. Finally, we
propose a feasible experiment to show a Fabry-Perot like effect for a high
dimensional two-photon state.Comment: 5 pages, 5 figure
Totally Secure Classical Communication Utilizing Johnson (-like) Noise and Kirchoff's Law
An absolutely secure, fast, inexpensive, robust, maintenance-free and
low-power- consumption communication is proposed. The states of the information
bit are represented by two resistance values. The sender and the receiver have
such resistors available and they randomly select and connect one of them to
the channel at the beginning of each clock period. The thermal noise voltage
and current can be observed but Kirchoff's law provides only a second-order
equation. A secure bit is communicated when the actual resistance values at the
sender's side and the receiver's side differ. Then the second order equation
yields the two resistance values but the eavesdropper is unable to determine
the actual locations of the resistors and to find out the state of the sender's
bit. The receiver knows that the sender has the inverse of his bit, similarly
to quantum entanglement. The eavesdropper can decode the message if, for each
bits, she inject current in the wire and measures the voltage change and the
current changes in the two directions. However, in this way she gets discovered
by the very first bit she decodes. Instead of thermal noise, proper external
noise generators should be used when the communication is not aimed to be
stealth.Comment: Physics Letters A, in press; Manuscript featured by Science, vol.
309, p. 2148 (2005, September 30
Tailoring photonic entanglement in high-dimensional Hilbert spaces
We present an experiment where two photonic systems of arbitrary dimensions
can be entangled. The method is based on spontaneous parametric down conversion
with trains of d pump pulses with a fixed phase relation, generated by a
mode-locked laser. This leads to a photon pair created in a coherent
superposition of discrete emission times, given by the successive laser
pulses. Entanglement is shown by performing a two-photon interference
experiment and by observing the visibility of the interference fringes
increasing as a function of the dimension d. Factors limiting the visibility,
such as the presence of multiple pairs in one train, are discussed.Comment: 4 pages, 4 figures, published versio
Experimental quantum key distribution based on a Bell test
We report on a complete free-space field implementation of a modified Ekert91
protocol for quantum key distribution using entangled photon pairs. For each
photon pair we perform a random choice between key generation and a Bell
inequality. The amount of violation is used to determine the possible knowledge
of an eavesdropper to ensure security of the distributed final key.Comment: 5 pages ReVTeX, 3 figures; version v2 with updated references and
minor corrections, author spelling fixe
Distribution of time-bin qubits over 50 km of optical fiber
We report experimental distribution of time-bin entangled qubits over 50 km
of optical fibers. Using actively stabilized preparation and measurement
devices we demonstrate violation of the CHSH Bell inequality by more than 15
standard deviations without removing the detector noise. In addition we report
a proof of principle experiment of quantum key distribution over 50 km of
optical fibers using entangled photon.Comment: 4 pages, 4 figure
Long distance quantum teleportation in a quantum relay configuration
A long distance quantum teleportation experiment with a fiber-delayed Bell
State Measurement (BSM) is reported. The source creating the qubits to be
teleported and the source creating the necessary entangled state are connected
to the beam splitter realizing the BSM by two 2 km long optical fibers. In
addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in
another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm
are teleported onto photons at 1550 nm. The fidelity is of 77%, above the
maximal value obtainable without entanglement. This is the first realization of
an elementary quantum relay over significant distances, which will allow an
increase in the range of quantum communication and quantum key distribution.Comment: 4 pages, submitte
Long distance entanglement swapping with photons from separated sources
We report the first experimental realization of entanglement swapping over
large distances in optical fibers. Two photons separated by more than two km of
optical fibers are entangled, although they never directly interacted. We use
two pairs of time-bin entangled qubits created in spatially separated sources
and carried by photons at telecommunication wavelengths. A partial Bell state
measurement is performed with one photon from each pair which projects the two
remaining photons, formerly independent onto an entangled state. A visibility
high enough to violate a Bell inequality is reported, after both photons have
each travelled through 1.1 km of optical fiber.Comment: 4 pages, 3 figures, submitte
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