101 research outputs found
Stimulation of Beta Decay due to a Bose-Einstein Condensate
Nuclear processes can be stimulated by the presence of a macroscopic number
of bosons in one of the final states. We describe the conditions necessary to
observe the atom-stimulation of a beta decay process. The stimulation may be
observable if it becomes possible to produce a Bose-Einstein condensate with
the order of atoms in a trap.Comment: 7 pages, LaTeX, uses elsart.cls, home page at
http://online.anu.edu.au/Physics/Welcome.htm
The linewidth of a non-Markovian atom laser
We present a fully quantum mechanical treatment of a single mode atom laser
including pumping and output coupling. By ignoring atom-atom interactions, we
have solved this model without making the Born-Markov approximation. We find
substantially less gain narrowing than is predicted under that approximation.Comment: 4 pages, 1 encapsulated postscript figur
Formation of a molecular Bose-Einstein condensate and an entangled atomic gas by Feshbach resonance
Processes of association in an atomic Bose-Einstein condensate, and
dissociation of the resulting molecular condensate, due to Feshbach resonance
in a time-dependent magnetic field, are analyzed incorporating non-mean-field
quantum corrections and inelastic collisions. Calculations for the Na atomic
condensate demonstrate that there exist optimal conditions under which about
80% of the atomic population can be converted to a relatively long-lived
molecular condensate (with lifetimes of 10 ms and more). Entangled atoms in
two-mode squeezed states (with noise reduction of about 30 dB) may also be
formed by molecular dissociation. A gas of atoms in squeezed or entangled
states can have applications in quantum computing, communications, and
measurements.Comment: LaTeX, 5 pages with 4 figures, uses REVTeX
Stationary quantum statistics of a non-Markovian atom laser
We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers.Comment: 12 pages, 2 figures, submitted to PR
Quantum statistical measurements of an atom laser beam
We describe a scheme, operating in a manner analogous to a reversed Raman
output coupler, for measuring the phase-sensitive quadrature statistics of an
atom laser beam. This scheme allows for the transferral of the atomic field
statistics to an optical field, for which the quantum statistics may then be
measured using the well-developed technology of optical homodyne measurement.Comment: 4 pages, 2 fugure
Systematic Review of Peer Support for Breastfeeding Continuation: Metaregression Analysis of the Effect of Setting, Intensity, and Timing
Objective To examine the effect of setting, intensity, and timing of peer support on breast feeding.
Design Systematic review and metaregression analysis of randomised controlled trials.
Data sources Cochrane Library, Medline, CINAHL, the National Research Register, and British Nursing Index were searched from inception or from 1980 to 2011.
Review methods Study selection, data abstraction, and quality assessment were carried out independently and in duplicate. Risk ratios and 95% confidence intervals were calculated for individual studies and pooled. Effects were estimated for studies grouped according to setting (high income countries, low or middle income countries, and the United Kingdom), intensity (<5 and ≥5 planned contacts), and timing of peer support (postnatal period with or without antenatal care), and analysed using metaregression for any and exclusive breast feeding at last study follow-up.
Results Peer support interventions had a significantly greater effect on any breast feeding in low or middle income countries (P<0.001), reducing the risk of not breast feeding at all by 30% (relative risk 0.70, 95% confidence interval 0.60 to 0.82) compared with a reduction of 7% (0.93, 0.87 to 1.00) in high income countries. Similarly, the risk of non-exclusive breast feeding decreased significantly more in low or middle income countries than in high income countries: 37% (0.63, 0.52 to 0.78) compared with 10% (0.90, 0.85 to 0.97); P=0.01. No significant effect on breast feeding was observed in UK based studies. Peer support had a greater effect on any breastfeeding rates when given at higher intensity (P=0.02) and only delivered in the postnatal period (P<0.001), although no differences were observed of its effect on exclusive breastfeeding rates by intensity or timing.
Conclusion Although peer support interventions increase breastfeeding continuation in low or middle income countries, especially exclusive breast feeding, this does not seem to apply in high income countries, particularly the United Kingdom, where breastfeeding support is part of routine postnatal healthcare. Peer support of low intensity does not seem to be effective. Policy relating to provision of peer support should be based on more specific evidence on setting and any new peer services in high income countries need to undergo concurrent evaluation
Band Gaps for Atoms in Light based Waveguides
The energy spectrum for a system of atoms in a periodic potential can exhibit
a gap in the band structure. We describe a system in which a laser is used to
produce a mechanical potential for the atoms, and a standing wave light field
is used to shift the atomic levels using the Autler-Townes effect, which
produces a periodic potential. The band structure for atoms guided by a hollow
optical fiber waveguide is calculated in three dimensions with quantised
external motion. The size of the band gap is controlled by the light guided by
the fiber. This variable band structure may allow the construction of devices
which can cool atoms. The major limitation on this device would be the
spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through
http://online.anu.edu.au/Physics/papers/atom.htm
An Atom Laser Based on Raman Transitions
In this paper we present an atom laser scheme using a Raman transition for
the output coupling of atoms. A beam of thermal atoms (bosons) in a metastable
atomic state are pumped into a multimode atomic cavity. This cavity is
coupled through spontaneous emission to a single mode of another cavity for the
ground atomic state, . Above a certain threshold pumping rate a large
number of atoms, , builds up in this single quantum state and transitions
to the ground state of the cavity become enhanced by a factor .
Atoms in this state are then coupled to the outside of the cavity with a Raman
transition. This changes the internal state of the atom and imparts a momentum
kick, allowing the atoms to leave the system.Comment: 8 pages, 4 postscript figures, uses RevTex, home page at
http://online.anu.edu.au/Physics/Welcome.html (Some aspects of the exact
physical model have changed from original version. Other general improvements
included
Photon blockade and quantum dynamics in intracavity coherent photoassociation of Bose-Einstein condensates
We demonstrate that a photon blockade effect exists in the intracavity coherent photoassociation of an atomic Bose-Einstein condensate and that the dynamics of the coupled atomic and molecular condensates can only be successfully described by a quantum treatment of all the interacting fields. We show that the usual mean-field calculational approaches give answers that are qualitatively wrong, even for the mean fields. The quantization of the fields gives a degree of freedom that is not present in analogous nonlinear optical processes. The difference between the semiclassical and quantum predictions can actually increase as the three fields increase in size so that there is no obvious classical limit for this process
Quantum correlated twin atomic beams via photo-dissociation of a molecular Bose-Einstein condensate
We study the process of photo-dissociation of a molecular Bose-Einstein
condensate as a potential source of strongly correlated twin atomic beams. We
show that the two beams can possess nearly perfect quantum squeezing in their
relative numbers.Comment: Corrected LaTeX file layou
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