943 research outputs found
``Plug and play'' systems for quantum cryptography
We present a time-multiplexed interferometer based on Faraday mirrors, and
apply it to quantum key distribution. The interfering pulses follow exactly the
same spatial path, ensuring very high stability and self balancing. Use of
Faraday mirrors compensates automatically any birefringence effects and
polarization dependent losses in the transmitting fiber. First experimental
results show a fringe visibility of 0.9984 for a 23km-long interferometer,
based on installed telecom fibers.Comment: LaTex, 6 pages, with 2 Postscript figures, Submitted to Applied
Physics Letter
Jordan-Wigner Approach to Dynamic Correlations in 2D Spin-1/2 Models
We discuss the dynamic properties of the square-lattice spin-1/2 XY model
obtained using the two-dimensional Jordan-Wigner fermionization approach. We
argue the relevancy of the fermionic picture for interpreting the neutron
scattering measurements in the two-dimensional frustrated quantum magnet
Cs_2CuCl_4.Comment: Presented at 12-th Czech and Slovak Conference on Magnetism,
Ko\v{s}ice, 12-15 July 200
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
Quantum Cryptography using larger alphabets
Like all of quantum information theory, quantum cryptography is traditionally
based on two level quantum systems. In this letter, a new protocol for quantum
key distribution based on higher dimensional systems is presented. An
experimental realization using an interferometric setup is also proposed.
Analyzing this protocol from the practical side, one finds an increased key
creation rate while keeping the initial laser pulse rate constant. Analyzing it
for the case of intercept/resend eavesdropping strategy, an increased error
rate is found compared to two dimensional systems, hence an advantage for the
legitimate users to detect an eavesdropper.Comment: 12 pages, 2 (eps) figure
Board diversity and financial performance : a graphical time-series approach
Directors need to guide and govern companies on behalf of and for the benefit of shareholders and
stakeholders. However questions remain as to whether boards with higher levels of diversity amongst
directors are better equipped to fulfil their fiduciary duty than boards with lower levels of diversity. This
research examines whether increased levels of diversity within boards are associated with improved
financial performance to shareholders. From the literature, several theoretical frameworks that could explain
why increased diversity might or might not lead to improved board performance were noted. Share returns
and directors’ demographic data were collected for a sample of the largest 40 companies listed on the JSE
from 2000 to 2013. This data was analysed using Muller and Ward’s (2013) investment style engine by
forming portfolios of companies based on board-diversity constructs. Time-series graphs of cumulative
portfolio market returns were analysed to determine if the diversity dimensions tested were associated with
improved share performance. The results show that racial diversity within boards is not associated with
financial performance. However, increased gender diversity and younger average board age are shown to
have strong associations with improved share price performance. These findings are mainly attributed to
agency-, resource dependency, human capital and signalling theories. Increased diversity is seen to bolster
independence and lessen agency problems. Rising diversity levels also enlarge boards’ external networks,
allowing diverse stakeholders’ needs to be accommodated and limiting dependence on strategic resources.
Finally, as human capital is increased, the collection of different skills and experiences are associated with
better performance. The results, based on a more robust methodology and improved data set, provide
additional support to previous studies.http://www.sajems.orgam2016Gordon Institute of Business Science (GIBS
Board diversity and financial performance : a graphical time-series approach
Directors need to guide and govern companies on behalf of and for the benefit of shareholders and
stakeholders. However questions remain as to whether boards with higher levels of diversity amongst
directors are better equipped to fulfil their fiduciary duty than boards with lower levels of diversity. This
research examines whether increased levels of diversity within boards are associated with improved
financial performance to shareholders. From the literature, several theoretical frameworks that could explain
why increased diversity might or might not lead to improved board performance were noted. Share returns
and directors’ demographic data were collected for a sample of the largest 40 companies listed on the JSE
from 2000 to 2013. This data was analysed using Muller and Ward’s (2013) investment style engine by
forming portfolios of companies based on board-diversity constructs. Time-series graphs of cumulative
portfolio market returns were analysed to determine if the diversity dimensions tested were associated with
improved share performance. The results show that racial diversity within boards is not associated with
financial performance. However, increased gender diversity and younger average board age are shown to
have strong associations with improved share price performance. These findings are mainly attributed to
agency-, resource dependency, human capital and signalling theories. Increased diversity is seen to bolster
independence and lessen agency problems. Rising diversity levels also enlarge boards’ external networks,
allowing diverse stakeholders’ needs to be accommodated and limiting dependence on strategic resources.
Finally, as human capital is increased, the collection of different skills and experiences are associated with
better performance. The results, based on a more robust methodology and improved data set, provide
additional support to previous studies.http://www.sajems.orgam2016Gordon Institute of Business Science (GIBS
Experimental realization of the one qubit Deutsch-Jozsa algorithm in a quantum dot
We perform quantum interference experiments on a single self-assembled
semiconductor quantum dot. The presence or absence of a single exciton in the
dot provides a qubit that we control with femtosecond time resolution. We
combine a set of quantum operations to realize the single-qubit Deutsch-Jozsa
algorithm. The results show the feasibility of single qubit quantum logic in a
semiconductor quantum dot using ultrafast optical control.Comment: REVTex4, 4 pages, 3 figures. Now includes more details about the
dephasing in the quantum dots. The introduction has been reworded for
clarity. Minor readability fixe
Phenomenological constraints on SUSY SU(5) GUTs with non-universal gaugino masses
We study phenomenological aspects of supersymmetric SU(5) grand unified
theories with non-universal gaugino masses. For large tan beta, we investigate
constraints from the requirement of successful electroweak symmetry breaking,
the positivity of stau mass squared and the b to s gamma decay rate. In the
allowed region, the nature of the lightest supersymmetric particle is
determined. Examples of mass spectra are given. We also calculate loop
corrections to the bottom mass due to superpartners.Comment: 10 pages, 2 figures (8 eps files), uses REVTeX. Replaced to match the
version to be published in PRD: minor corrections and addition
HYPERION: An open-source parallelized three-dimensional dust continuum radiative transfer code
HYPERION is a new three-dimensional dust continuum Monte-Carlo radiative
transfer code that is designed to be as generic as possible, allowing radiative
transfer to be computed through a variety of three-dimensional grids. The main
part of the code is problem-independent, and only requires an arbitrary
three-dimensional density structure, dust properties, the position and
properties of the illuminating sources, and parameters controlling the running
and output of the code. HYPERION is parallelized, and is shown to scale well to
thousands of processes. Two common benchmark models for protoplanetary disks
were computed, and the results are found to be in excellent agreement with
those from other codes. Finally, to demonstrate the capabilities of the code,
dust temperatures, SEDs, and synthetic multi-wavelength images were computed
for a dynamical simulation of a low-mass star formation region. HYPERION is
being actively developed to include new features, and is publicly available
(http://www.hyperion-rt.org).Comment: Accepted for publication in Astronomy & Astrophysics. HYPERION is
being prepared for release at the start of 2012, but you can already sign up
to the mailing list at http://www.hyperion-rt.org to be informed once it is
available for downloa
One-Way Entangled-Photon Autocompensating Quantum Cryptography
A new quantum cryptography implementation is presented that combines one-way
operation with an autocompensating feature that has hitherto only been
available in implementations that require the signal to make a round trip
between the users. Using the concept of advanced waves, it is shown that this
new implementation is related to the round-trip implementations in the same way
that Ekert's two-particle scheme is related to the original one-particle scheme
of Bennett and Brassard. The practical advantages and disadvantages of the
proposed implementation are discussed in the context of existing schemes.Comment: 5 pages, 1 figure; Minor edits--conclusions unchanged; accepted for
publication in Physical Review
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