23,893 research outputs found
Real time demonstration of high bitrate quantum random number generation with coherent laser light
We present a random number generation scheme that uses broadband measurements
of the vacuum field contained in the radio-frequency sidebands of a single-mode
laser. Even though the measurements may contain technical noise, we show that
suitable algorithms can transform the digitized photocurrents into a string of
random numbers that can be made arbitrarily correlated with a subset of the
quantum fluctuations (high quantum correlation regime) or arbitrarily immune to
environmental fluctuations (high environmental immunity). We demonstrate up to
2 Gbps of real time random number generation that were verified using standard
randomness tests
High efficiency coherent optical memory with warm rubidium vapour
By harnessing aspects of quantum mechanics, communication and information
processing could be radically transformed. Promising forms of quantum
information technology include optical quantum cryptographic systems and
computing using photons for quantum logic operations. As with current
information processing systems, some form of memory will be required. Quantum
repeaters, which are required for long distance quantum key distribution,
require optical memory as do deterministic logic gates for optical quantum
computing. In this paper we present results from a coherent optical memory
based on warm rubidium vapour and show 87% efficient recall of light pulses,
the highest efficiency measured to date for any coherent optical memory. We
also show storage recall of up to 20 pulses from our system. These results show
that simple warm atomic vapour systems have clear potential as a platform for
quantum memory
An AC Stark Gradient Echo Memory in Cold Atoms
The burgeoning fields of quantum computing and quantum key distribution have
created a demand for a quantum memory. The gradient echo memory scheme is a
quantum memory candidate for light storage that can boast efficiencies
approaching unity, as well as the flexibility to work with either two or three
level atoms. The key to this scheme is the frequency gradient that is placed
across the memory. Currently the three level implementation uses a Zeeman
gradient and warm atoms. In this paper we model a new gradient creation
mechanism - the ac Stark effect - to provide an improvement in the flexibility
of gradient creation and field switching times. We propose this scheme in
concert with a move to cold atoms (~1 mK). These temperatures would increase
the storage times possible, and the small ensemble volumes would enable large
ac Stark shifts with reasonable laser power. We find that memory bandwidths on
the order of MHz can be produced with experimentally achievable laser powers
and trapping volumes, with high precision in gradient creation and switching
times on the order of nanoseconds possible. By looking at the different
decoherence mechanisms present in this system we determine that coherence times
on the order of 10s of milliseconds are possible, as are delay-bandwidth
products of approximately 50 and efficiencies over 90%
Storage and Manipulation of Light Using a Raman Gradient Echo Process
The Gradient Echo Memory (GEM) scheme has potential to be a suitable protocol
for storage and retrieval of optical quantum information. In this paper, we
review the properties of the -GEM method that stores information in
the ground states of three-level atomic ensembles via Raman coupling. The
scheme is versatile in that it can store and re-sequence multiple pulses of
light. To date, this scheme has been implemented using warm rubidium gas cells.
There are different phenomena that can influence the performance of these
atomic systems. We investigate the impact of atomic motion and four-wave mixing
and present experiments that show how parasitic four-wave mixing can be
mitigated. We also use the memory to demonstrate preservation of pulse shape
and the backward retrieval of pulses.Comment: 26 pages, 13 figure
Biased EPR entanglement and its application to teleportation
We consider pure continuous variable entanglement with non-equal correlations
between orthogonal quadratures. We introduce a simple protocol which equates
these correlations and in the process transforms the entanglement onto a state
with the minimum allowed number of photons. As an example we show that our
protocol transforms, through unitary local operations, a single squeezed beam
split on a beam splitter into the same entanglement that is produced when two
squeezed beams are mixed orthogonally. We demonstrate that this technique can
in principle facilitate perfect teleportation utilising only one squeezed beam.Comment: 8 pages, 5 figure
Gauge Consistent Wilson Renormalization Group II: Non-Abelian Case
We give a wilsonian formulation of non-abelian gauge theories explicitly
consistent with axial gauge Ward identitities. The issues of unitarity and
dependence on the quantization direction are carefully investigated. A
wilsonian computation of the one-loop QCD beta function is performed.Comment: 34 pages, 1 eps figure, latex2e. Minor changes, version to appear in
Int. J. Mod. Phy
Engine dynamic analysis with general nonlinear finite element codes. Part 2: Bearing element implementation overall numerical characteristics and benchmaking
Finite element codes are used in modelling rotor-bearing-stator structure common to the turbine industry. Engine dynamic simulation is used by developing strategies which enable the use of available finite element codes. benchmarking the elements developed are benchmarked by incorporation into a general purpose code (ADINA); the numerical characteristics of finite element type rotor-bearing-stator simulations are evaluated through the use of various types of explicit/implicit numerical integration operators. Improving the overall numerical efficiency of the procedure is improved
String Organization of Field Theories: Duality and Gauge Invariance
String theories should reduce to ordinary four-dimensional field theories at
low energies. Yet the formulation of the two are so different that such a
connection, if it exists, is not immediately obvious. With the Schwinger
proper-time representation, and the spinor helicity technique, it has been
shown that field theories can indeed be written in a string-like manner, thus
resulting in simplifications in practical calculations, and providing novel
insights into gauge and gravitational theories. This paper continues the study
of string organization of field theories by focusing on the question of local
duality. It is shown that a single expression for the sum of many diagrams can
indeed be written for QED, thereby simulating the duality property in strings.
The relation between a single diagram and the dual sum is somewhat analogous to
the relation between a old- fashioned perturbation diagram and a Feynman
diagram. Dual expressions are particularly significant for gauge theories
because they are gauge invariant while expressions for single diagrams are not.Comment: 20 pages in Latex, including seven figures in postscrip
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