2,188 research outputs found
Comment on 'Quantum inversion of cold atoms in a microcavity: spatial dependence'
In a recent work, Abdel-Aty and Obada [2002 J. Phys. B 35 807-813] analyzed
the quantum inversion of cold atoms in a microcavity, the motion of the atoms
being described quantum mechanically. Two-level atoms were assumed to interact
with a single mode of the cavity, and the off-resonance case was considered
(namely the atomic transition frequency is detuned from the single mode cavity
frequency). We demonstrate in this paper that this case is incorrectly treated
by these authors and we question therefore their conclusions.Comment: 4 pages, no figure
Isotope shifts and hyperfine structure of the laser cooling Fe I 358-nm line
We report on the measurement of the isotope shifts of the Fe~I line at 358~nm between all four
stable isotopes Fe, Fe, Fe and Fe, as well
as the hyperfine structure of that line for Fe, the only stable
isotope having a nonzero nuclear spin. This line is of primary importance for
laser cooling applications. In addition, an experimental value of the field and
specific mass shift coefficients of the transition is reported as well as the
hyperfine structure magnetic dipole coupling constant of the transition
excited state in Fe, namely
MHz. The measurements were carried out by means of laser-induced fluorescence
spectroscopy performed on an isotope-enriched iron atomic beam. All measured
frequency shifts are reported with uncertainties below the third percent level.Comment: 5 pages, 5 figure
Operational Entanglement Families of Symmetric Mixed N-Qubit States
We introduce an operational entanglement classification of symmetric mixed
states for an arbitrary number of qubits based on stochastic local operations
assisted with classical communication (SLOCC operations). We define families of
SLOCC entanglement classes successively embedded into each other, we prove that
they are of non-zero measure, and we construct witness operators to distinguish
them. Moreover, we discuss how arbitrary symmetric mixed states can be realized
in the lab via a one-to-one correspondence between well-defined sets of
controllable parameters and the corresponding entanglement families.Comment: 6 pages, 2 figures, published version, Phys. Rev. A, in pres
Detuning effects in the one-photon mazer
The quantum theory of the mazer in the non-resonant case (a detuning between
the cavity mode and the atomic transition frequencies is present) is written.
The generalization from the resonant case is far from being direct. Interesting
effects of the mazer physics are pointed out. In particular, it is shown that
the cavity may slow down or speed up the atoms according to the sign of the
detuning and that the induced emission process may be completely blocked by use
of a positive detuning. It is also shown that the detuning adds a potential
step effect not present at resonance and that the use of positive detunings
defines a well-controlled cooling mechanism. In the special case of a mesa
cavity mode function, generalized expressions for the reflection and
transmission coefficients have been obtained. The general properties of the
induced emission probability are finally discussed in the hot, intermediate and
cold atom regimes. Comparison with the resonant case is given.Comment: 9 pages, 8 figure
Entanglement Equivalence of -qubit Symmetric States
We study the interconversion of multipartite symmetric -qubit states under
stochastic local operations and classical communication (SLOCC). We demonstrate
that if two symmetric states can be connected with a nonsymmetric invertible
local operation (ILO), then they belong necessarily to the separable, W, or GHZ
entanglement class, establishing a practical method of discriminating subsets
of entanglement classes. Furthermore, we prove that there always exists a
symmetric ILO connecting any pair of symmetric -qubit states equivalent
under SLOCC, simplifying the requirements for experimental implementations of
local interconversion of those states.Comment: Minor correction
Chemical abundances for Hf 2-2, a planetary nebula with the strongest known heavy element recombination lines
We present high quality optical spectroscopic observations of the planetary
nebula (PN) Hf 2-2. The spectrum exhibits many prominent optical recombination
lines (ORLs) from heavy element ions. Analysis of the H {\sc i} and He {\sc i}
recombination spectrum yields an electron temperature of K, a factor
of ten lower than given by the collisionally excited [O {\sc iii}] forbidden
lines. The ionic abundances of heavy elements relative to hydrogen derived from
ORLs are about a factor of 70 higher than those deduced from collisionally
excited lines (CELs) from the same ions, the largest abundance discrepancy
factor (adf) ever measured for a PN. By comparing the observed O {\sc ii}
4089/4649 ORL ratio to theoretical value as a function of
electron temperature, we show that the O {\sc ii} ORLs arise from ionized
regions with an electron temperature of only K. The current
observations thus provide the strongest evidence that the nebula contains
another previously unknown component of cold, high metallicity gas, which is
too cool to excite any significant optical or UV CELs and is thus invisible via
such lines. The existence of such a plasma component in PNe provides a natural
solution to the long-standing dichotomy between nebular plasma diagnostics and
abundance determinations using CELs on the one hand and ORLs on the other.Comment: 12 pages, 5 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Obtention d'alliages réfractaires SiCxNy(O) par dépôt chimique à oartir d'une gazeuse Si(CH3)4-NH3
By pure thermal CVD from Si(CH/sub 3/)/sub 4/NH/sub 3/ mixtures SiC/sub x/N/sub y/(O) films have been prepared at 1475 K. Using electron microprobe analysis a continuous composition variation between SiC and Si/sub 3/N/sub 4/ is shown. The difficulty of quantitative analysis due to the conductivity of the samples is underlined. By selecting the right conditions, precise measurements were obtained. These films have an optical energy band gap in the range 2.2-4.1 eV and a constant photoluminescence peak. The film structure is discussed and these materials may be probably ascribed to an alloy phas
Description and Predictive Factors of individual outcomes in a refugee camp based mental health intervention (Beirut, Lebanon)
There is little evidence on the effectiveness of services for the care of people with mental disorders among refugee populations. Médecins sans Frontières (MSF) has established a mental health centre in a mixed urban-refugee population in Beirut to respond to the significant burden of mental health problems. Patients received comprehensive care through a multidisciplinary team. A cohort of people with common and severe mental disorders has been analysed between December 2008 and June 2011 to evaluate individual outcomes of treatment in terms of functionality
Quantum Imaging with Incoherent Photons
We propose a technique to obtain sub-wavelength resolution in quantum imaging
with potentially 100% contrast using incoherent light. Our method requires
neither path-entangled number states nor multi-photon absorption. The scheme
makes use of N photons spontaneously emitted by N atoms and registered by N
detectors. It is shown that for coincident detection at particular detector
positions a resolution of \lambda / N can be achieved.Comment: 4 pages, 3 figures, improved presentation. Accepted in Physical
Review Letter
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