323 research outputs found
Experimental Vacuum Squeezing in Rubidium Vapor via Self-Rotation
We report the generation of optical squeezed vacuum states by means of
polarization self-rotation in rubidium vapor following a proposal by Matsko et
al. [Phys. Rev. A 66, 043815 (2002)]. The experimental setup, involving in
essence just a diode laser and a heated rubidium gas cell, is simple and easily
scalable. A squeezing of 0.85+-0.05 dB was achieved
Conditional large Fock state preparation and field state reconstruction in Cavity QED
We propose a scheme for producing large Fock states in Cavity QED via the
implementation of a highly selective atom-field interaction. It is based on
Raman excitation of a three-level atom by a classical field and a quantized
field mode. Selectivity appears when one tunes to resonance a specific
transition inside a chosen atom-field subspace, while other transitions remain
dispersive, as a consequence of the field dependent electronic energy shifts.
We show that this scheme can be also employed for reconstructing, in a new and
efficient way, the Wigner function of the cavity field state.Comment: 4 Revtex pages with 3 postscript figures. Submitted for publicatio
Quantum correlations and fluctuations in the pulsed light produced by a synchronously pumped optical parametric oscillator below its oscillation threshold
We present a simple quantum theory for the pulsed light generated by a
synchronously pumped optical parametric oscillator (SPOPO) in the degenerate
case where the signal and idler trains of pulses coincide, below threshold and
neglecting all dispersion effects. Our main goal is to precise in the obtained
quantum effects, which ones are identical to the c.w. case and which ones are
specific to the SPOPO. We demonstrate in particular that the temporal
correlations have interesting peculiarities: the quantum fluctuations at
different times within the same pulse turn out to be totally not correlated,
whereas they are correlated between nearby pulses at times that are placed in
the same position relative to the centre of the pulses. The number of
significantly correlated pulses is of the order of cavity finesse. We show also
that there is perfect squeezing at noise frequencies multiple of the pulse
repetition frequency when one approaches the threshold from below on the signal
field quadrature measured by a balanced homodyne detection with a local
oscillator of very short duration compared to the SPOPO pulse length.Comment: 12 pages, 3 figure
In-loop squeezing is real squeezing to an in-loop atom
Electro-optical feedback can produce an in-loop photocurrent with arbitrarily
low noise. This is not regarded as evidence of `real' squeezing because
squeezed light cannot be extracted from the loop using a linear beam splitter.
Here I show that illuminating an atom (which is a nonlinear optical element)
with `in-loop' squeezed light causes line-narrowing of one quadrature of the
atom's fluorescence. This has long been regarded as an effect which can only be
produced by squeezing. Experiments on atoms using in-loop squeezing should be
much easier than those with conventional sources of squeezed light.Comment: 4 pages, 2 figures, submitted to PR
Four-Wave mixing in degenerate Fermi gases: Beyond the undepleted pump approximation
We analyze the full nonlinear dynamics of the four-wave mixing between an
incident beam of fermions and a fermionic density grating. We find that when
the number of atoms in the beam is comparable to the number of atoms forming
the grating, the dephasing of that grating, which normally leads to a decay of
its amplitude, is suppressed. Instead, the density grating and the beam density
exhibit large nonlinear coupled amplitude oscillations. In this case four-wave
mixing can persist for much longer times compared to the case of negligible
back-action. We also evaluate the efficiency of the four-wave mixing and show
that it can be enhanced by producing an initial density grating with an
amplitude that is less than the maximum value. These results indicate that
efficient four-wave mixing in fermionic alkali gases should be experimentally
observable.Comment: 9 pages, 8 figure
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An overview of ISCAT 2000
The Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) took place over the timer period of 15 November to 31 December in the year 2000. The study location was the Amundsen Scott Station in Antarctica. ISCAT 2000 defines the second phase of a program designed to explore tropospheric chemistry in Antarctica. As in 1998, the 2000 ISCAT study revealed a strong oxidizing environment at South Pole (SP). During the 2000 investigation, however, the suite of measurements was greatly expanded. These new measurements established the recycling of reactive nitrogen as a critical component of this unique environment. This paper first presents the historical background leading up to the ISCAT 2000 observations; then it focuses on providing a summary of the year 2000 results and contrasts these with those recorded during 1998. Important developments made during the 2000 study included the recording of SP data for several species being emitted from the snowpack. These included NO, H 2O2 and CH2O. In this context, eddy-diffusion flux measurements provided the first quantitative estimates of the SP NO and NOx snow-to-atmosphere fluxes. This study also revealed that HNO 3 and HO2NO2 were major sink species for HOx and NOx radicals. And, it identified the critical factors responsible for SP NO levels exceeding those at other polar sites by nearly an order of magnitude. Finally, it reports on the levels of gas phase sulfur species and provides evidence indicating that the absence of DMS at SP is most likely due to its greatly shorten chemical lifetime in the near vicinity of the plateau. It is proposed that this is due to the influence of NO on the distribution of OH in the lower free troposphere over a region that extends well beyond the plateau itself. Details related to each of the above findings plus others can be found in the 11 accompanying Special Issue papers. © 2004 Elsevier Ltd. All rights reserved
Neonatal jaundice and developmental impairment among infants in Kilifi, Kenya
Background: Neonatal jaundice (NNJ) is common in subâSaharan Africa (SSA), and it is associated with sepsis. Despite the high incidence, little has been documented about developmental impairments associated with NNJ in SSA. In particular, it is not clear if sepsis is associated with greater impairment following NNJ.
Methods: We followed up 169 participants aged 12 months (57 cases and 112 controls) within the Kilifi Health Demographic Surveillance System. The diagnosis of NNJ was based on clinical laboratory measurement of total serum bilirubin on admission, whereas the developmental outcomes were assessed using the Developmental Milestones Checklist and Kilifi Development Inventory.
Results: There were significant differences between the cases and controls in all developmental domains. Cases scored lower in language functioning (mean [M] = 6.5, standard deviation [SD] = 4.3 vs. M = 8.9, SD = 4.6; p \u3c .001); psychomotor functioning (Mdn = 23, interquartile range [IQR] = 17â34 vs. Mdn = 31.0, IQR = 22.0â44.0; MannâWhitney U = 4,122, p = .002); and socioâemotional functioning ([Mdn = 30.0, IQR = 27.0â33.0 vs. Mdn = 34.0, IQR = 30.0â37.0], MannâWhitney U = 4,289, p \u3c .001). There was no evidence of association between sepsis and psychomotor (rpb = â.2, p = .214), language (rpb = â.1, p = .510), and socioâemotional functioning (rpb = .0, p = .916). Significant and medium to large portions of the variance (34â64%) in the developmental outcomes among children who survived NNJ were associated with home birth, low maternal education, and feeding problems during the first days of life.
Conclusions: NNJ is associated with developmental impairments in the early childhood years; however, NNJ associated with sepsis does not lead to more severe impairment. Prenatal and postnatal care services are needed to reduce the negative impact of NNJ for children from low resourced settings
Frequency selection by soliton excitation in nondegenerate intracavity downconversion
We show that soliton excitation in intracavity downconversion naturally
selects a strictly defined frequency difference between the signal and idler
fields. In particular, this phenomenon implies that if the signal has smaller
losses than the idler then its frequency is pulled away from the cavity
resonance and the idler frequency is pulled towards the resonance and {\em vice
versa}. The frequency selection is shown to be closely linked with the relative
energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let
Spatiotemporally Localized Multidimensional Solitons in Self-Induced Transparency Media
"Light bullets" are multi-dimensional solitons which are localized in both
space and time. We show that such solitons exist in two- and three-dimensional
self-induced-transparency media and that they are fully stable. Our approximate
analytical calculation, backed and verified by direct numerical simulations,
yields the multi-dimensional generalization of the one-dimensional Sine-Gordon
soliton.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Demonstration of integrated microscale optics in surface-electrode ion traps
In ion trap quantum information processing, efficient fluorescence collection
is critical for fast, high-fidelity qubit detection and ion-photon
entanglement. The expected size of future many-ion processors require scalable
light collection systems. We report on the development and testing of a
microfabricated surface-electrode ion trap with an integrated high numerical
aperture (NA) micromirror for fluorescence collection. When coupled to a low NA
lens, the optical system is inherently scalable to large arrays of mirrors in a
single device. We demonstrate stable trapping and transport of 40Ca+ ions over
a 0.63 NA micromirror and observe a factor of 1.9 enhancement in photon
collection compared to the planar region of the trap.Comment: 15 pages, 8 figure
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