1,425 research outputs found
On the energy and pseudo-angle of Frenet vector fields in Rⁿᵥ
In this paper, we compute the energy of a Frenet vector field and the pseudo-angle between Frenet vectors for a given non-null curve C in semi-Euclidean space of signature (n,v). It is shown that the energy and pseudo-angle can be expressed in terms of the curvature functions of C.Обчислено енергiю векторного поля Френе та псевдокут мiж векторами Френе для заданої ненульової кривої C у напiвевклiдовому просторi сигнатури (n,v). Показано, що енергiя та псевдокут можуть бути вираженi через функцiї кривини C
Antiresonance phase shift in strongly coupled cavity QED
We investigate phase shifts in the strong coupling regime of single-atom
cavity quantum electrodynamics (QED). On the light transmitted through the
system, we observe a phase shift associated with an antiresonance and show that
both its frequency and width depend solely on the atom, despite the strong
coupling to the cavity. This shift is optically controllable and reaches 140
degrees - the largest ever reported for a single emitter. Our result offers a
new technique for the characterization of complex integrated quantum circuits.Comment: 5 pages, 5 figure
The Robust Network Loading Problem under Hose Demand Uncertainty: Formulation, Polyhedral Analysis, and Computations
Cataloged from PDF version of article.We consider the network loading problem (NLP) under a polyhedral uncertainty description of traffic
demands. After giving a compact multicommodity flow formulation of the problem, we state a decomposition
property obtained from projecting out the flow variables. This property considerably simplifies the
resulting polyhedral analysis and computations by doing away with metric inequalities. Then we focus on a
specific choice of the uncertainty description, called the “hose model,” which specifies aggregate traffic upper
bounds for selected endpoints of the network. We study the polyhedral aspects of the NLP under hose demand
uncertainty and use the results as the basis of an efficient branch-and-cut algorithm. The results of extensive
computational experiments on well-known network design instances are reported
Rb-85 tunable-interaction Bose-Einstein condensate machine
We describe our experimental setup for creating stable Bose-Einstein
condensates of Rb-85 with tunable interparticle interactions. We use
sympathetic cooling with Rb-87 in two stages, initially in a tight
Ioffe-Pritchard magnetic trap and subsequently in a weak, large-volume crossed
optical dipole trap, using the 155 G Feshbach resonance to manipulate the
elastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85
condensates contain 4 x 10^4 atoms with a scattering length of a=+200a_0. Our
minimalist apparatus is well-suited to experiments on dual-species and spinor
Rb condensates, and has several simplifications over the Rb-85 BEC machine at
JILA (Papp, 2007; Papp and Wieman, 2006), which we discuss at the end of this
article.Comment: 10 pages, 8 figure
Quantum projection noise limited interferometry with coherent atoms in a Ramsey type setup
Every measurement of the population in an uncorrelated ensemble of two-level
systems is limited by what is known as the quantum projection noise limit.
Here, we present quantum projection noise limited performance of a Ramsey type
interferometer using freely propagating coherent atoms. The experimental setup
is based on an electro-optic modulator in an inherently stable Sagnac
interferometer, optically coupling the two interfering atomic states via a
two-photon Raman transition. Going beyond the quantum projection noise limit
requires the use of reduced quantum uncertainty (squeezed) states. The
experiment described demonstrates atom interferometry at the fundamental noise
level and allows the observation of possible squeezing effects in an atom
laser, potentially leading to improved sensitivity in atom interferometers.Comment: 8 pages, 8 figures, published in Phys. Rev.
Effect of twine thickness on selectivity of gillnets for bogue, Boops boops,in Turkish waters
To investigate the effect of twine thickness on the selectivity of multifilament gillnet targeting bogue,Boops boops L., four different stations were sampled between March and November 2008 in the northern Aegean Sea. Gillnets with 22, 23, and 25 mm nominal mesh size (bar length) each having two different twine thicknesses (approximately 0.45 mm and 0.54 mm ∅) were applied for this purpose. The deviances from the SELECT method revealed that lognormal models provided the best fits for both of the twine thicknesses. Results from the two-way ANOVA analyses revealed that the mean total lengths increased with the mesh size (F = 87.36; df = 2; P < 0.0001) and decreased with the twine thickness (F = 46.12; df = 1; P < 0.0001). The 22 mm mesh size net (0.45 mm ∅) captured significantly larger fish than the 23 mm mesh size net (0.54 mm ∅) probably due to the higher elasticity and flexibility of the thinner twine. Thus, fisheries managers should take into consideration the twine thickness while advising mesh size regulations in gillnet fisheries
Optically trapped atom interferometry using the clock transition of large Rb-87 Bose-Einstein condensates
We present a Ramsey-type atom interferometer operating with an optically
trapped sample of 10^6 Bose-condensed Rb-87 atoms. The optical trap allows us
to couple the |F =1, mF =0>\rightarrow |F =2, mF =0> clock states using a
single photon 6.8GHz microwave transition, while state selective readout is
achieved with absorption imaging. Interference fringes with contrast
approaching 100% are observed for short evolution times. We analyse the process
of absorption imaging and show that it is possible to observe atom number
variance directly, with a signal-to-noise ratio ten times better than the
atomic projection noise limit on 10^6 condensate atoms. We discuss the
technical and fundamental noise sources that limit our current system, and
outline the improvements that can be made. Our results indicate that, with
further experimental refinements, it will be possible to produce and measure
the output of a sub-shot-noise limited, large atom number BEC-based
interferometer.
In an addendum to the original paper, we attribute our inability to observe
quantum projection noise to the stability of our microwave oscillator and
background magnetic field. Numerical simulations of the Gross-Pitaevskii
equations for our system show that dephasing due to spatial dynamics driven by
interparticle interactions account for much of the observed decay in fringe
visibility at long interrogation times. The simulations show good agreement
with the experimental data when additional technical decoherence is accounted
for, and suggest that the clock states are indeed immiscible. With smaller
samples of 5 \times 10^4 atoms, we observe a coherence time of {\tau} =
(1.0+0.5-0.3) s.Comment: 22 pages, 6 figures Addendum: 11 pages, 6 figure
Gradient echo memory in an ultra-high optical depth cold atomic ensemble
Quantum memories are an integral component of quantum repeaters - devices
that will allow the extension of quantum key distribution to communication
ranges beyond that permissible by passive transmission. A quantum memory for
this application needs to be highly efficient and have coherence times
approaching a millisecond. Here we report on work towards this goal, with the
development of a Rb magneto-optical trap with a peak optical depth of
1000 for the D2 transition using spatial and temporal
dark spots. With this purpose-built cold atomic ensemble to implement the
gradient echo memory (GEM) scheme. Our data shows a memory efficiency of % and coherence times up to 195 s, which is a factor of four greater
than previous GEM experiments implemented in warm vapour cells.Comment: 15 pages, 5 figure
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