3,121 research outputs found
Observation of coherent many-body Rabi oscillations
A two-level quantum system coherently driven by a resonant electromagnetic
field oscillates sinusoidally between the two levels at frequency
which is proportional to the field amplitude [1]. This phenomenon, known as the
Rabi oscillation, has been at the heart of atomic, molecular and optical
physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi
oscillations in isolated single atoms or dilute gases form the basis for
metrological applications such as atomic clocks and precision measurements of
physical constants [3]. Both inhomogeneous distribution of coupling strength to
the field and interactions between individual atoms reduce the visibility of
the oscillation and may even suppress it completely. A remarkable
transformation takes place in the limit where only a single excitation can be
present in the sample due to either initial conditions or atomic interactions:
there arises a collective, many-body Rabi oscillation at a frequency
involving all N >> 1 atoms in the sample [4]. This is true even
for inhomogeneous atom-field coupling distributions, where single-atom Rabi
oscillations may be invisible. When one of the two levels is a strongly
interacting Rydberg level, many-body Rabi oscillations emerge as a consequence
of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to
quantum information processing based on this effect [5]. Here we report initial
observations of coherent many-body Rabi oscillations between the ground level
and a Rydberg level using several hundred cold rubidium atoms. The strongly
pronounced oscillations indicate a nearly complete excitation blockade of the
entire mesoscopic ensemble by a single excited atom. The results pave the way
towards quantum computation and simulation using ensembles of atoms
Postural instability in an immersive Virtual Reality adapts with repetition and includes directional and gender specific effects
The ability to handle sensory conflicts and use the most appropriate sensory information is vital for successful recovery of human postural control after injury. The objective was to determine if virtual reality (VR) could provide a vehicle for sensory training, and determine the temporal and spatial nature of such adaptive changes. Twenty healthy subjects participated in the study (10 females). The subjects watched a 90-second VR simulation of railroad (rollercoaster) motion in mountainous terrain during five repeated simulations, while standing on a force platform that recorded their stability. The immediate response to watching the VR movie was an increased level of postural instability. Repeatedly watching the same VR movie significantly reduced both the anteroposterior (62%, p < 0.001) and lateral (47%, p = 0.001) energy used. However, females adapted more slowly to the VR stimuli as reflected by higher use of total (p = 0.007), low frequency (p = 0.027) and high frequency (p = 0.026) energy. Healthy subjects can significantly adapt to a multidirectional, provocative, visual environment after 4–5 repeated sessions of VR. Consequently, VR technology might be an effective tool for rehabilitation involving visual desensitisation. However, some females may require more training sessions to achieve effects with VR
Can spacetime curvature induced corrections to Lamb shift be observable?
The Lamb shift results from the coupling of an atom to vacuum fluctuations of
quantum fields, so corrections are expected to arise when the spacetime is
curved since the vacuum fluctuations are modified by the presence of spacetime
curvature. Here, we calculate the curvature-induced correction to the Lamb
shift outside a spherically symmetric object and demonstrate that this
correction can be remarkably significant outside a compact massive
astrophysical body. For instance, for a neutron star or a stellar mass black
hole, the correction is 25% at a radial distance of ,
16% at and as large as 1.6% even at , where is
the mass of the object, the Newtonian constant, and the speed of light.
In principle, we can look at the spectra from a distant compact super-massive
body to find such corrections. Therefore, our results suggest a possible way of
detecting fundamental quantum effects in astronomical observations.Comment: 13 pages, 3 figures, slight title change, clarifications and more
discussions added, version to be published in JHE
Gastric Outlet Obstruction at Bugando Medical Centre in Northwestern Tanzania: A Prospective Review of 184 Cases.
Gastric outlet obstruction poses diagnostic and therapeutic challenges to general surgeons practicing in resource-limited countries. There is a paucity of published data on this subject in our setting. This study was undertaken to highlight the etiological spectrum and treatment outcome of gastric outlet obstruction in our setting and to identify prognostic factors for morbidity and mortality. This was a descriptive prospective study which was conducted at Bugando Medical Centre between March 2009 and February 2013. All patients with a clinical diagnosis of gastric outlet obstruction were, after informed consent for the study, consecutively enrolled into the study. Statistical data analysis was done using SPSS computer software version 17.0. A total of 184 patients were studied. More than two-third of patients were males. Patients with malignant gastric outlet obstruction were older than those of benign type. This difference was statistically significant (p < 0.001). Gastric cancer was the commonest malignant cause of gastric outlet obstruction where as peptic ulcer disease was the commonest benign cause. In children, the commonest cause of gastric outlet obstruction was congenital pyloric stenosis (13.0%). Non-bilious vomiting (100%) and weight loss (93.5%) were the most frequent symptoms. Eighteen (9.8%) patients were HIV positive with the median CD 4+ count of 282 cells/μl. A total of 168 (91.3%) patients underwent surgery. Of these, gastro-jejunostomy (61.9%) was the most common surgical procedure performed. The complication rate was 32.1 % mainly surgical site infections (38.2%). The median hospital stay and mortality rate were 14 days and 18.5% respectively. The presence of postoperative complication was the main predictor of hospital stay (p = 0.002), whereas the age > 60 years, co-existing medical illness, malignant cause, HIV positivity, low CD 4 count (<200 cells/μl), high ASA class and presence of surgical site infection significantly predicted mortality ( p< 0.001). The follow up of patients was generally poor as more than 60% of patients were lost to follow up. Gastric outlet obstruction in our setting is more prevalent in males and the cause is mostly malignant. The majority of patients present late with poor general condition. Early recognition of the diagnosis, aggressive resuscitation and early institution of surgical management is of paramount importance if morbidity and mortality associated with gastric outlet obstruction are to be avoided
Cryotomography of budding influenza a virus reveals filaments with diverse morphologies that mostly do not bear a genome at their distal end
Influenza viruses exhibit striking variations in particle morphology between strains. Clinical isolates of influenza A virus have been shown to produce long filamentous particles while laboratory-adapted strains are predominantly spherical. However, the role of the filamentous phenotype in the influenza virus infectious cycle remains undetermined. We used cryo-electron tomography to conduct the first three-dimensional study of filamentous virus ultrastructure in particles budding from infected cells. Filaments were often longer than 10 microns and sometimes had bulbous heads at their leading ends, some of which contained tubules we attribute to M1 while none had recognisable ribonucleoprotein (RNP) and hence genome segments. Long filaments that did not have bulbs were infrequently seen to bear an ordered complement of RNPs at their distal ends. Imaging of purified virus also revealed diverse filament morphologies; short rods (bacilliform virions) and longer filaments. Bacilliform virions contained an ordered complement of RNPs while longer filamentous particles were narrower and mostly appeared to lack this feature, but often contained fibrillar material along their entire length. The important ultrastructural differences between these diverse classes of particles raise the possibility of distinct morphogenetic pathways and functions during the infectious process
Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled Optical Lattices
We show that the recent experimental realization of spin-orbit coupling in
ultracold atomic gases can be used to study different types of spin spiral
order and resulting multiferroic effects. Spin-orbit coupling in optical
lattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which
is essential for spin spiral order. By taking into account spin-orbit coupling
and an external Zeeman field, we derive an effective spin model in the Mott
insulator regime at half filling and demonstrate that the DM interaction in
optical lattices can be made extremely strong with realistic experimental
parameters. The rich finite temperature phase diagrams of the effective spin
models for fermions and bosons are obtained via classical Monte Carlo
simulations.Comment: 7 pages, 5 figure
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