301 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
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
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
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
Nonclassical statistics of intracavity coupled waveguides: the quantum optical dimer
A model is proposed where two nonlinear waveguides are contained
in a cavity suited for second-harmonic generation. The evanescent wave coupling
between the waveguides is considered as weak, and the interplay between this
coupling and the nonlinear interaction within the waveguides gives rise to
quantum violations of the classical limit. These violations are particularly
strong when two instabilities are competing, where twin-beam behavior is found
as almost complete noise suppression in the difference of the fundamental
intensities. Moreover, close to bistable transitions perfect twin-beam
correlations are seen in the sum of the fundamental intensities, and also the
self-pulsing instability as well as the transition from symmetric to asymmetric
states display nonclassical twin-beam correlations of both fundamental and
second-harmonic intensities. The results are based on the full quantum Langevin
equations derived from the Hamiltonian and including cavity damping effects.
The intensity correlations of the output fields are calculated
semi-analytically using a linearized version of the Langevin equations derived
through the positive-P representation. Confirmation of the analytical results
are obtained by numerical simulations of the nonlinear Langevin equations
derived using the truncated Wigner representation.Comment: 15 pages, 8 figures, submitted to Phys. Rev.
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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
Spin-Nematic Squeezed Vacuum in a Quantum Gas
Using squeezed states it is possible to surpass the standard quantum limit of
measurement uncertainty by reducing the measurement uncertainty of one property
at the expense of another complementary property. Squeezed states were first
demonstrated in optical fields and later with ensembles of pseudo spin-1/2
atoms using non-linear atom-light interactions. Recently, collisional
interactions in ultracold atomic gases have been used to generate a large
degree of quadrature spin squeezing in two-component Bose condensates. For
pseudo spin-1/2 systems, the complementary properties are the different
components of the total spin vector , which fully characterize the state on
an SU(2) Bloch sphere. Here, we measure squeezing in a spin-1 Bose condensate,
an SU(3) system, which requires measurement of the rank-2 nematic or quadrupole
tensor as well to fully characterize the state. Following a quench
through a nematic to ferromagnetic quantum phase transition, squeezing is
observed in the variance of the quadratures up to -8.3(-0.7 +0.6) dB
(-10.3(-0.9 +0.7) dB corrected for detection noise) below the standard quantum
limit. This spin-nematic squeezing is observed for negligible occupation of the
squeezed modes and is analogous to optical two-mode vacuum squeezing. This work
has potential applications to continuous variable quantum information and
quantum-enhanced magnetometry
Alternative approach to electromagnetic field quantization in nonlinear and inhomogeneous media
A simple approach is proposed for the quantization of the electromagnetic
field in nonlinear and inhomogeneous media. Given the dielectric function and
nonlinear susceptibilities, the Hamiltonian of the electromagnetic field is
determined completely by this quantization method. From Heisenberg's equations
we derive Maxwell's equations for the field operators. When the nonlinearity
goes to zero, this quantization method returns to the generalized canonical
quantization procedure for linear inhomogeneous media [Phys. Rev. A, 43, 467,
1991]. The explicit Hamiltonians for the second-order and third-order nonlinear
quasi-steady-state processes are obtained based on this quantization procedure.Comment: Corrections in references and introductio
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
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