637 research outputs found
Efficient photon counting and single-photon generation using resonant nonlinear optics
The behavior of an atomic double lambda system in the presence of a strong
off-resonant classical field and a few-photon resonant quantum field is
examined. It is shown that the system possesses properties that allow a
single-photon state to be distilled from a multi-photon input wave packet. In
addition, the system is also capable of functioning as an efficient
photodetector discriminating between one- and two-photon wave packets with
arbitrarily high efficiency.Comment: 4 pages, 2 figure
Quantum theory of resonantly enhanced four-wave mixing: mean-field and exact numerical solutions
We present a full quantum analysis of resonant forward four-wave mixing based
on electromagnetically induced transparency (EIT). In particular, we study the
regime of efficient nonlinear conversion with low-intensity fields that has
been predicted from a semiclassical analysis. We derive an effective nonlinear
interaction Hamiltonian in the adiabatic limit. In contrast to conventional
nonlinear optics this Hamiltonian does not have a power expansion in the fields
and the conversion length increases with the input power. We analyze the
stationary wave-mixing process in the forward scattering configuration using an
exact numerical analysis for up to input photons and compare the results
with a mean-field approach. Due to quantum effects, complete conversion from
the two pump fields into the signal and idler modes is achieved only
asymptotically for large coherent pump intensities or for pump fields in
few-photon Fock states. The signal and idler fields are perfectly quantum
correlated which has potential applications in quantum communication schemes.
We also discuss the implementation of a single-photon phase gate for continuous
quantum computation.Comment: 10 pages, 11 figure
Low-light-level nonlinear optics with slow light
Electromagnetically induced transparency in an optically thick, cold medium
creates a unique system where pulse-propagation velocities may be orders of
magnitude less than and optical nonlinearities become exceedingly large. As
a result, nonlinear processes may be efficient at low-light levels. Using an
atomic system with three, independent channels, we demonstrate a quantum
interference switch where a laser pulse with an energy density of
photons per causes a 1/e absorption of a second pulse.Comment: to be published in PR
ANALISIS PERGERAKAN MATA UANG EUR/AUD DAN GBP/JPY DENGAN MENGGUNAKAN MOVING AVERAGE, PARABOLIC SAR DAN RELATIVE STRENGTH INDEX (RSI) PADA TIME FRAME 1 JAM PERIODE 4 MARET 2013 - 3 JUNI 2013
ANALISIS PERGERAKAN MATA UANG EUR/AUD DAN GBP/JPY DENGAN MENGGUNAKAN MOVING AVERAGE, PARABOLIC SAR DAN RELATIVE STRENGTH INDEX (RSI) PADA TIME FRAME 1 JAM PERIODE 4 MARET 2013 - 3 JUNI 2013
Effect of headlocks on milk production and feed intake of dairy cattle
Cows previously trained with headlocks
did not increase milk production or feed
intake when headlocks were removed. Twoyear-
old and older cows did not differ in
response to headlocks and neckrails. Prudent
use of headlocks increases labor efficiency
of a commercial dairy. Managing a dairy
without headlocks is a challenge because
cows must be sorted and worked off the
milking parlor flow. In the case of large
milking parlors, it may be necessary to process
50-200 cows per hour. Depending upon
the treatment facilities, this number of cows
may create a bottleneck in the dairy. For
many routine procedures, headlocks offer the
simplest and most cost-effective alternative.
It is important to note that headlocks can be
mismanaged. This is especially true during
summer months. Locking up cows for extended
periods without access to water or
shade may have adverse effects during summer
heat stress. It is important to minimize
lock-up time. Consideration should also be
given to training heifers to headlocks prior to
calving. It is very likely that untrained
heifers may be reluctant to be placed in
headlocks. If this occurs, intake could be
limited during their first exposure to
headlocks. If heifers are not trained to headlocks
prior to calving, one should determine
if they should be locked-up each day during
the first week of lactation. Headlocks can be
successfully used on a dairy. The critical
question is how will they be managed.
Successful managers of headlocks minimize
restraint time, push-up or feed pens often (6-
8 times per day), and avoid use of headlocks
during late morning and afternoon hours
during the summer months
Single photon production by rephased amplified spontaneous emission
The production of single photons using rephased amplified spontaneous emission is examined. This process produces single photons on demand with high efficiency by detecting the spontaneous emission from an atomic ensemble, then applying a population-inverting pulse to rephase the ensemble and produce a photon echo of the spontaneous emission events. The theoretical limits on the efficiency of the production are determined for several variants of the scheme. For an ensemble of uniform optical density, generating the initial spontaneous emission and its echo using transitions of different strengths is shown to produce single photons at 70% efficiency, limited by reabsorption. Tailoring the spatial and spectral density of the atomic ensemble is then shown to prevent reabsorption of the rephased photon, resulting in emission efficiency near unity
Nursing churn and turnover in Australian hospitals:Nurses perceptions and suggestions for supportive strategies
BACKGROUND: This study aimed to reveal nursesâ experiences and perceptions of turnover in Australian hospitals and identify strategies to improve retention, performance and job satisfaction. Nursing turnover is a serious issue that can compromise patient safety, increase health care costs and impact on staff morale. A qualitative design was used to analyze responses from 362 nurses collected from a national survey of nurses from medical and surgical nursing units across 3 Australian States/Territories. METHOD: A qualitative design was used to analyze responses from 362 nurses collected from a national survey of nurses from medical and surgical nursing units across 3 Australian States/Territories. RESULTS: Key factors affecting nursing turnover were limited career opportunities; poor support; a lack of recognition; and negative staff attitudes. The nursing working environment is characterised by inappropriate skill-mix and inadequate patient-staff ratios; a lack of overseas qualified nurses with appropriate skills; low involvement in decision-making processes; and increased patient demands. These issues impacted upon heavy workloads and stress levels with nurses feeling undervalued and disempowered. Nurses described supportive strategies: improving performance appraisals, responsive preceptorship and flexible employment options. CONCLUSION: Nursing turnover is influenced by the experiences of nurses. Positive steps can be made towards improving workplace conditions and ensuring nurse retention. Improving performance management and work design are strategies that nurse managers could harness to reduce turnover
Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets
We analyze both analytically and numerically the resonant four-wave mixing of
two co-propagating single-photon wave packets. We present analytic expressions
for the two-photon wave function and show that soliton-type quantum solutions
exist which display a shape-preserving oscillatory exchange of excitations
between the modes. Potential applications including quantum information
processing are discussed.Comment: 7 pages, 3 figure
The fossil record of early tetrapods: worker effort and the end-Permian mass extinction
It is important to understand the quality of the fossil record of early tetrapods (Tetrapoda, minus Lissamphibia and Amniota) because of their key role in the transition of vertebrates from water to land, their dominance of terrestrial faunas for over 100 million years of the late Palaeozoic and earlyMesozoic, and their variable fates during the endâPermian mass extinction. The first description of an early tetrapod dates back to 1824, and since then discoveries have occurred at a rather irregular pace, with peaks and troughs corresponding to some of the vicissitudes of human history through the past two centuries. As expected, the record is dominated by the wellâsampled sedimentary basins of Europe and North America, but finds from other continents are increasing rapidly. Comparisons of snapshots of knowledge in 1900, 1950, and 2000 show that discovery of new species has changed the shape of the speciesâlevel diversification curve, contrary to earlier studies of familyâlevel taxa. There is, however, little evidence that taxon counts relate to research effort (as counted by numbers of publications), and there are no biasing effects associated with differential study of different time intervals through the late Palaeozoic and Mesozoic. In fact, levels of effort are apparently not related to geological time, with no evidence that workers have spent more time on more recent parts of the record. In particular, the endâPermian mass extinction was investigated to determine whether diversity changes through that interval might reflect worker effort: it turns out that most records of early tetrapod taxa (when corrected for duration of geological series) occur in the Lower Triassic
The Grover algorithm with large nuclear spins in semiconductors
We show a possible way to implement the Grover algorithm in large nuclear
spins 1/2<I<9/2 in semiconductors. The Grover sequence is performed by means of
multiphoton transitions that distribute the spin amplitude between the nuclear
spin states. They are distinguishable due to the quadrupolar splitting, which
makes the nuclear spin levels non-equidistant. We introduce a generalized
rotating frame for an effective Hamiltonian that governs the non-perturbative
time evolution of the nuclear spin states for arbitrary spin lengths I. The
larger the quadrupolar splitting, the better the agreement between our
approximative method using the generalized rotating frame and exact numerical
calculations.Comment: 11 pages, 18 EPS figures, REVTe
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