318 research outputs found
Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity
We study the interaction of an atom with a quantum guided field in a weakly
driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian
and derive the density-matrix equations for the combined atom-cavity system. We
calculate the mean photon number, the second-order photon correlation function,
and the atomic excited-state population. We show that, due to the confinement
of the guided cavity field in the fiber cross-section plane and in the space
between the FBG mirrors, the presence of the atom in the FBG cavity can
significantly affect the mean photon number and the photon statistics even
though the cavity finesse is moderate, the cavity is long, and the probe field
is weak.Comment: Accepted for Phys. Rev.
Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas
We experimentally study the group time delay for a light pulse propagating
through hot Rb vapor in the presence of a strong coupling field in a
configuration. We demonstrate that the ultra-slow pulse propagation is
transformed into superluminal propagation as the one-photon detuning of the
light increases due to the change in the transmission resonance lineshape.
Negative group velocity as low as -c/10^6=-80 m/s is recorded. We also find
that the advance time in the regime of the superluminal propagation grows
linearly with increasing laser field power.Comment: 5 pages, 6 figure
The effect of magnesium vacancies on the intraband scattering in MgxB2 as determined by point contact Andreev reflection
In order to introduce structural defects into the band with minimal distortions in the band, bulk samples of varying magnesium content were prepared. Point contact Andreev reflection measurements reveal that the density of states of the band and the behavior of the energy gaps in
field imply a relative increase of band to band scattering with increasing magnesium deficiency.
The results are consistent with the observed increase of the low temperature Hc2 value in magnesium deficient MgB2
Slow Light Propagation in a Thin Optical Fiber via Electromagnetically Induced Transparency
We propose a novel configuration that utilizes electromagnetically induced
transparency (EIT) to tailor a fiber mode propagating inside a thin optical
fiber and coherently control its dispersion properties to drastically reduce
the group velocity of the fiber mode. The key to this proposal is: the
evanescent-like field of the thin fiber strongly couples with the surrounding
active medium, so that the EIT condition is met by the medium. We show how the
properties of the fiber mode is modified due to the EIT medium, both
numerically and analytically. We demonstrate that the group velocity of the new
modified fiber mode can be drastically reduced (approximately 44 m/sec) using
the coherently prepared orthohydrogen doped in a matrix of parahydrogen crystal
as the EIT medium.Comment: 10 pages in two column RevTex4, 6 Figure
Linear atomic quantum coupler
In this paper, we develop the notion of the linear atomic quantum coupler.
This device consists of two modes propagating into two waveguides, each of them
includes a localized and/or a trapped atom. These waveguides are placed close
enough to allow exchanging energy between them via evanescent waves. Each mode
interacts with the atom in the same waveguide in the standard way, i.e. as the
Jaynes-Cummings model (JCM), and with the atom-mode in the second waveguide via
evanescent wave. We present the Hamiltonian for the system and deduce the exact
form for the wavefunction. We investigate the atomic inversions and the
second-order correlation function. In contrast to the conventional linear
coupler, the atomic quantum coupler is able to generate nonclassical effects.
The atomic inversions can exhibit long revival-collapse phenomenon as well as
subsidiary revivals based on the competition among the switching mechanisms in
the system. Finally, under certain conditions, the system can yield the results
of the two-mode JCM.Comment: 14 pages, 3 figures; comments are most welcom
Optical nanofibers and spectroscopy
We review our recent progress in the production and characterization of
tapered optical fibers with a sub-wavelength diameter waist. Such fibers
exhibit a pronounced evanescent field and are therefore a useful tool for
highly sensitive evanescent wave spectroscopy of adsorbates on the fiber waist
or of the medium surrounding. We use a carefully designed flame pulling process
that allows us to realize preset fiber diameter profiles. In order to determine
the waist diameter and to verify the fiber profile, we employ scanning electron
microscope measurements and a novel accurate in situ optical method based on
harmonic generation. We use our fibers for linear and non-linear absorption and
fluorescence spectroscopy of surface-adsorbed organic molecules and investigate
their agglomeration dynamics. Furthermore, we apply our spectroscopic method to
quantum dots on the surface of the fiber waist and to caesium vapor surrounding
the fiber. Finally, towards dispersive measurements, we present our first
results on building and testing a single-fiber bi-modal interferometer.Comment: 13 pages, 18 figures. Accepted for publication in Applied Physics B.
Changes according to referee suggestions: changed title, clarification of
some points in the text, added references, replacement of Figure 13
Scattering of massless particles in one-dimensional chiral channel
We present a general formalism describing a propagation of an arbitrary
multiparticle wave packet in a one-dimensional multimode chiral channel coupled
to an ensemble of emitters which are distributed at arbitrary positions. The
formalism is based on a direct and exact resummation of diagrammatic series for
the multiparticle scattering matrix. It is complimentary to the Bethe Ansatz
and to approaches based on equations of motion, and it reveals a simple and
transparent structure of scattering states. In particular, we demonstrate how
this formalism works on various examples, including scattering of one- and
two-photon states off two- and three-level emitters, off an array of emitters
as well as scattering of coherent light. We argue that this formalism can be
constructively used for study of scattering of an arbitrary initial photonic
state off emitters with arbitrary degree of complexity.Comment: 25 pages, 5 figure
Differential maturation and subcellular localization of severe acute respiratory syndrome coronavirus surface proteins S, M and E
Post-translational modifications and correct subcellular localization of viral structural proteins are prerequisites for assembly and budding of enveloped viruses. Coronaviruses, like the severe acute respiratory syndrome-associated virus (SARS-CoV), bud from the endoplasmic reticulum-Golgi intermediate compartment. In this study, the subcellular distribution and maturation of SARS-CoV surface proteins S, M and E were analysed by using C-terminally tagged proteins. As early as 30 min post-entry into the endoplasmic reticulum, high-mannosylated S assembles into trimers prior to acquisition of complex N-glycans in the Golgi. Like S, M acquires high-mannose N-glycans that are subsequently modified into complex N-glycans in the Golgi. The N-glycosylation profile and the absence of O-glycosylation on M protein relate SARS-CoV to the previously described group 1 and 3 coronaviruses. Immunofluorescence analysis shows that S is detected in several compartments along the secretory pathway from the endoplasmic reticulum to the plasma membrane while M predominantly localizes in the Golgi, where it accumulates, and in trafficking vesicles. The E protein is not glycosylated. Pulse-chase labelling and confocal microscopy in the presence of protein translation inhibitor cycloheximide revealed that the E protein has a short half-life of 30 min. E protein is found in bright perinuclear patches colocalizing with endoplasmic reticulum markers. In conclusion, SARS-CoV surface proteins S, M and E show differential subcellular localizations when expressed alone suggesting that additional cellular or viral factors might be required for coordinated trafficking to the virus assembly site in the endoplasmic reticulum-Golgi intermediate compartment. © 2005 SGM.postprin
An approach to exact solutions of the time-dependent supersymmetric two-level three-photon Jaynes-Cummings model
By utilizing the property of the supersymmetric structure in the two-level
multiphoton Jaynes-Cummings model, an invariant is constructed in terms of the
supersymmetric generators by working in the sub-Hilbert-space corresponding to
a particular eigenvalue of the conserved supersymmetric generators. We obtain
the exact solutions of the time-dependent Schr\"{o}dinger equation which
describes the time-dependent supersymmetric two-level three-photon
Jaynes-Cummings model (TLTJCM) by using the invariant-related unitary
transformation formulation. The case under the adiabatic approximation is also
discussed.
Keywords: Supersymmetric Jaynes-Cummings model; exact solutions; invariant
theory; geometric phase factor; adiabatic approximationComment: 7 pages, Late
Comparative susceptibility of mosquito populations in North Queensland, Australia to oral infection with dengue virus.
Dengue is the most prevalent arthropod-borne virus, with at least 40% of the world's population at risk of infection each year. In Australia, dengue is not endemic, but viremic travelers trigger outbreaks involving hundreds of cases. We compared the susceptibility of Aedes aegypti mosquitoes from two geographically isolated populations to two strains of dengue virus serotype 2. We found, interestingly, that mosquitoes from a city with no history of dengue were more susceptible to virus than mosquitoes from an outbreak-prone region, particularly with respect to one dengue strain. These findings suggest recent evolution of population-based differences in vector competence or different historical origins. Future genomic comparisons of these populations could reveal the genetic basis of vector competence and the relative role of selection and stochastic processes in shaping their differences. Lastly, we show the novel finding of a correlation between midgut dengue titer and titer in tissues colonized after dissemination
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