61 research outputs found
Correlated motion of two atoms trapped in a single mode cavity field
We study the motion of two atoms trapped at distant positions in the field of
a driven standing wave high-Q optical resonator. Even without any direct
atom-atom interaction the atoms are coupled through their position dependent
influence on the intracavity field. For sufficiently good trapping and low
cavity losses the atomic motion becomes significantly correlated and the two
particles oscillate in their wells preferentially with a 90 degrees relative
phase shift. The onset of correlations seriously limits cavity cooling
efficiency, raising the achievable temperature to the Doppler limit. The
physical origin of the correlation can be traced back to a cavity mediated
cross-friction, i.e. a friction force on one particle depending on the velocity
of the second particle. Choosing appropriate operating conditions allows for
engineering these long range correlations. In addition this cross-friction
effect can provide a basis for sympathetic cooling of distant trapped clouds.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev. A. Minor
grammatical changes to previous versio
Quantum rings as electron spin beam splitters
Quantum interference and spin-orbit interaction in a one-dimensional
mesoscopic semiconductor ring with one input and two output leads can act as a
spin beam splitter. Different polarization can be achieved in the two output
channels from an originally totally unpolarized incoming spin state, very much
like in a Stern-Gerlach apparatus. We determine the relevant parameters such
that the device has unit efficiency.Comment: 4 pages, 3 figures; minor change
Self-organization of a Bose-Einstein condensate in an optical cavity
The spatial self-organization of a Bose-Einstein condensate (BEC) in a
high-finesse linear optical cavity is discussed. The condensate atoms are
laser-driven from the side and scatter photons into the cavity. Above a
critical pump intensity the homogeneous condensate evolves into a stable
pattern bound by the cavity field. The transition point is determined
analytically from a mean-field theory. We calculate the lowest lying Bogoliubov
excitations of the coupled BEC-cavity system and the quantum depletion due to
the atom-field coupling.Comment: 11 pages, final version. Accepted for publication in EPJ
Multimode mean-field model for the quantum phase transition of a Bose-Einstein condensate in an optical resonator
We develop a mean-field model describing the Hamiltonian interaction of
ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate
is properly defined by means of a grand-canonical approach. The model is
efficient because only the relevant excitation modes are taken into account.
However, the model goes beyond the two-mode subspace necessary to describe the
self-organization quantum phase transition observed recently. We calculate all
the second-order correlations of the coupled atom field and radiation field
hybrid bosonic system, including the entanglement between the two types of
fields.Comment: 10 page
Transcription analysis of the myometrium of labouring and non-labouring women
An incomplete understanding of the molecular mechanisms that initiate normal human labour at term seriously hampers the development of effective ways to predict, prevent and treat disorders such as preterm labour. Appropriate analysis of large microarray experiments that compare gene expression in non-labouring and labouring gestational tissues is necessary to help bridge these gaps in our knowledge. In this work, gene expression in 48 (22 labouring, 26 non-labouring) lower-segment myometrial samples collected at Caesarean section were analysed using Illumina HT-12 v4.0 BeadChips. Normalised data were compared between labouring and non-labouring groups using traditional statistical methods and a novel network graph approach. We sought technical validation with quantitative real-time PCR, and biological replication through inverse variance-weighted meta-analysis with published microarray data. We have extended the list of genes suggested to be associated with labour: Compared to non-labouring samples, labouring samples showed apparent higher expression at 960 probes (949 genes) and apparent lower expression at 801 probes (789 genes) (absolute fold change ≥1.2, rank product percentage of false positive value (RP-PFP) <0.05). Although half of the women in the labouring group had received pharmaceutical treatment to induce or augment labour, sensitivity analysis suggested that this did not confound our results. In agreement with previous studies, functional analysis suggested that labour was characterised by an increase in the expression of inflammatory genes and network analysis suggested a strong neutrophil signature. Our analysis also suggested that labour is characterised by a decrease in the expression of muscle-specific processes, which has not been explicitly discussed previously. We validated these findings through the first formal meta-analysis of raw data from previous experiments and we hypothesise that this represents a change in the composition of myometrial tissue at labour. Further work will be necessary to reveal whether these results are solely due to leukocyte infiltration into the myometrium as a mechanism initiating labour, or in addition whether they also represent gene changes in the myocytes themselves. We have made all our data available at www.ebi.ac.uk/arrayexpress/ (accession number E-MTAB-3136) to facilitate progression of this work
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