1,740 research outputs found
Electro-Optical Nanotraps for Neutral Atoms
We propose a new class of nanoscale electro-optical traps for neutral atoms.
A prototype is the toroidal trap created by a suspended, charged carbon
nanotube decorated with a silver nanosphere dimer. An illuminating laser field,
blue detuned from an atomic resonance frequency, is strongly focused by
plasmons induced in the dimer and generates both a repulsive potential barrier
near the nanostructure surface and a large viscous damping force that
facilitates trap loading. Atoms with velocities of several meters per second
may be loaded directly into the trap via spontaneous emission of just two
photons.Comment: 5 pages, 3 figures. Fig. 1 appeared on the cover of the January 23,
2009 issue of PR
Biomolecular imaging and electronic damage using X-ray free-electron lasers
Proposals to determine biomolecular structures from diffraction experiments
using femtosecond X-ray free-electron laser (XFEL) pulses involve a conflict
between the incident brightness required to achieve diffraction-limited atomic
resolution and the electronic and structural damage induced by the
illumination. Here we show that previous estimates of the conditions under
which biomolecular structures may be obtained in this manner are unduly
restrictive, because they are based on a coherent diffraction model that is not
appropriate to the proposed interaction conditions. A more detailed imaging
model derived from optical coherence theory and quantum electrodynamics is
shown to be far more tolerant of electronic damage. The nuclear density is
employed as the principal descriptor of molecular structure. The foundations of
the approach may also be used to characterize electrodynamical processes by
performing scattering experiments on complex molecules of known structure.Comment: 16 pages, 2 figure
Enhancing capacity of coherent optical information storage and transfer in a Bose-Einstein condensate
Coherent optical information storage capacity of an atomic Bose-Einstein
condensate is examined. Theory of slow light propagation in atomic clouds is
generalized to short pulse regime by taking into account group velocity
dispersion. It is shown that the number of stored pulses in the condensate can
be optimized for a particular coupling laser power, temperature and interatomic
interaction strength. Analytical results are derived for semi-ideal model of
the condensate using effective uniform density zone approximation. Detailed
numerical simulations are also performed. It is found that axial density
profile of the condensate protects the pulse against the group velocity
dispersion. Furthermore, taking into account finite radial size of the
condensate, multi-mode light propagation in atomic Bose-Einstein condensate is
investigated. The number of modes that can be supported by a condensate is
found. Single mode condition is determined as a function of experimentally
accessible parameters including trap size, temperature, condensate number
density and scattering length. Quantum coherent atom-light interaction schemes
are proposed for enhancing multi-mode light propagation effects.Comment: 12pages. Laser Physics, in pres
Immunospecific Antibody Concentration in Egg Yolk of Chickens Orally Immunised with Varying Doses of Bovine Serum Albumin and the Mucosal Adjuvant, RhinoVax®, using Different Immunization Regimes
Antibody harvested from eggs of immunised chickens, IgY, has proven to be a non-invasive alternative to antibodies purified from serum of mammals. Taking the non-invasive concept further, the development of oral immunization techniques combined with IgY harvest from chicken eggs may subsequently eliminate all regulated procedures from polyclonal antibody production. In the present study, we report the effects of varying the temporal administration mode of the antigen (immunogen) comparing dosing on three consecutive days with dosing on five consecutive days, and of incorporating a mucosal adjuvant. Two antigen doses were compared: 30 mg bovine serum albumin (BSA) and 300 mg BSA, with and without the mucosal adjuvant, RhinoVax®, administered to laying chickens. The egg yolk of chickens dosed with BSA in combination with 20% RhinoVax®, contained significantly higher concentrations of immunospecific IgY than did egg yolks of chickens fed with BSA without adjuvant. The most efficient dose in the RhinoVax®-treated groups was 300 mg BSA regardless of whether the chickens were initially immunised daily for three or five days. A 3-day dosing regime with BSA alone also induced immunospecific IgY production. This study confirms that RhinoVax® is an efficient oral adjuvant. It also demonstrates the efficacy of daily immunizations on three or five consecutive days on immunospecific IgY production. The chickens received oral booster immunizations one and two months after the initial immunization. No real effect could be recorded after the second and third immunization, although the study did provide some evidence of memory based on an optimum IgY concentration recorded after the 2nd immunization.
Making SPIFFI SPIFFIER: Upgrade of the SPIFFI instrument for use in ERIS and performance analysis from re-commissioning
SPIFFI is an AO-fed integral field spectrograph operating as part of SINFONI
on the VLT, which will be upgraded and reused as SPIFFIER in the new VLT
instrument ERIS. In January 2016, we used new technology developments to
perform an early upgrade to optical subsystems in the SPIFFI instrument so
ongoing scientific programs can make use of enhanced performance before ERIS
arrives in 2020. We report on the upgraded components and the performance of
SPIFFI after the upgrade, including gains in throughput and spatial and
spectral resolution. We show results from re-commissioning, highlighting the
potential for scientific programs to use the capabilities of the upgraded
SPIFFI. Finally, we discuss the additional upgrades for SPIFFIER which will be
implemented before it is integrated into ERIS.Comment: 20 pages, 12 figures. Proceedings from SPIE Astronomical Telescopes
and Instrumentation 201
Relativistic Effects of Light in Moving Media with Extremely Low Group Velocity
A moving dielectric medium acts as an effective gravitational field on light.
One can use media with extremely low group velocities [Lene Vestergaard Hau et
al., Nature 397, 594 (1999)] to create dielectric analogs of astronomical
effects on Earth. In particular, a vortex flow imprints a long-ranging
topological effect on incident light and can behave like an optical black hole.Comment: Physical Review Letters (accepted
Stability of Bose-Einstein Condensates Confined in Traps
Bose-Einstein condensation has been realized in dilute atomic vapors. This
achievement has generated immerse interest in this field. Presented is a review
of recent theoretical research into the properties of trapped dilute-gas
Bose-Einstein condensates. Among them, stability of Bose-Einstein condensates
confined in traps is mainly discussed. Static properties of the ground state
are investigated by use of the variational method. The anlysis is extended to
the stability of two-component condensates. Time-development of the condensate
is well-described by the Gross-Pitaevskii equation which is known in nonlinear
physics as the nonlinear Schr\"odinger equation. For the case that the
inter-atomic potential is effectively attractive, a singularity of the solution
emerges in a finite time. This phenomenon which we call collapse explains the
upper bound for the number of atoms in such condensates under traps.Comment: 74 pages with 12 figures, submitted to the review section of
International Journal of Modern Physics
Limitations of light delay and storage times in EIT experiments with condensates
We investigate the limitations arising from atomic collisions on the storage
and delay times of probe pulses in EIT experiments. We find that the atomic
collisions can be described by an effective decay rate that limits storage and
delay times. We calculate the momentum and temperature dependence of the decay
rate and find that it is necessary to excite atoms at a particular momentum
depending on temperature and spacing of the energy levels involved in order to
minimize the decoherence effects of atomic collisions.Comment: 4 pages RevTeX, 4 figures. Send correspondence to
[email protected]
Storage of light in atomic vapor
We report an experiment in which a light pulse is decelerated and trapped in
a vapor of Rb atoms, stored for a controlled period of time, and then released
on demand. We accomplish this storage of light by dynamically reducing the
group velocity of the light pulse to zero, so that the coherent excitation of
the light is reversibly mapped into a collective Zeeman (spin) coherence of the
Rb vapor
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