3,665 research outputs found
Multiphoton resonance in a three-level system with nearly degenerate excited states
An analytic study is presented of the efficient multiphoton excitation and
strong harmonic generation in three-level systems specified by a pair of nearly
degenerate, strongly dipole-coupled excited states. Such systems are physically
formed by the three lowest states in, e.g., the hydrogen atom or evenly charged
homonuclear diatomic molecular ions under reasonably chosen laser intensities.
As a detailed analytic result, we found that the laser pulse of photon energy
, duration and intensity is able to produce complete inversion of
the initial population in the hydrogen atom through the 5-photon excitation. At
the same photon energy, the pulse of duration and intensity
was found to produce the
same effect in the molecular ion but through the 9-photon excitation. We show
that the accompanying scattering of light has very rich spectrum differing
substantially from that of the two-level system.Comment: 9 pages, 5 figures,submitted to Phys. Rev. A, comments welcom
Interacting double dark resonances in a hot atomic vapor of helium
We experimentally and theoretically study two different tripod configurations
using metastable helium (He*), with the probe field polarization
perpendicular and parallel to the quantization axis, defined by an applied weak
magnetic field. In the first case, the two dark resonances interact
incoherently and merge together into a single EIT peak with increasing coupling
power. In the second case, we observe destructive interference between the two
dark resonances inducing an extra absorption peak at the line center.Comment: 7 pages, 7 figure
Atom-molecule coexistence and collective dynamics near a Feshbach resonance of cold fermions
Degenerate Fermi gas interacting with molecules near Feshbach resonance is
unstable with respect to formation of a mixed state in which atoms and
molecules coexist as a coherent superposition. Theory of this state is
developed using a mapping to the Dicke model, treating molecular field in the
single mode approximation. The results are accurate in the strong coupling
regime relevant for current experimental efforts. The exact solution of the
Dicke model is exploited to study stability, phase diagram, and nonadiabatic
dynamics of molecular field in the mixed state.Comment: 5 pages, 2 figure
Correlations in atomic systems: Diagnosing coherent superpositions
While investigating quantum correlations in atomic systems, we note that
single measurements contain information about these correlations. Using a
simple model of measurement -- analogous to the one used in quantum optics --
we show how to extract higher order correlation functions from individual
"phtotographs" of the atomic sample. As a possible application we apply the
method to detect a subtle phase coherence in mesoscopic superpostitions.Comment: 4 pages, 2 figures, provisionally accepted to Physical Review Letter
Modification of radiation pressure due to cooperative scattering of light
Cooperative spontaneous emission of a single photon from a cloud of N atoms
modifies substantially the radiation pressure exerted by a far-detuned laser
beam exciting the atoms. On one hand, the force induced by photon absorption
depends on the collective decay rate of the excited atomic state. On the other
hand, directional spontaneous emission counteracts the recoil induced by the
absorption. We derive an analytical expression for the radiation pressure in
steady-state. For a smooth extended atomic distribution we show that the
radiation pressure depends on the atom number via cooperative scattering and
that, for certain atom numbers, it can be suppressed or enhanced.Comment: 8 pages, 2 Figure
Photonic band gap via quantum coherence in vortex lattices of Bose gases
We investigate the optical response of an atomic Bose-Einstein condensate
with a vortex lattice. We find that it is possible for the vortex lattice to
act as a photonic crystal and create photonic band gaps, by enhancing the
refractive index of the condensate via a quantum coherent scheme. If high
enough index contrast between the vortex core and the atomic sample is
achieved, a photonic band gap arises depending on the healing length and the
lattice spacing. A wide range of experimentally accessible parameters are
examined and band gaps in the visible region of the electromagnetic spectrum
are found. We also show how directional band gaps can be used to directly
measure the rotation frequency of the condensate.Comment: 4 pages, 4 figures, Final version to appear in PR
Hydrogen interactions in aluminum-lithium alloys
A program is described which seeks to develop an understanding of the effects of dissolved and trapped hydrogen on the mechanical properties of selected Al-Li-Cu-X alloys. A proposal is made to distinguish hydrogen (H2) induced EAC from aqueous dissolution controlled EAC, to correlate H2 induced EAC with mobile and trapped concentrations, and to identify significant trap sites and hydride phases (if any) through use of model alloys and phases. A literature review shows three experimental factors which have impeded progress in the area of H2 EAC for this class of alloys. These are as listed: (1) inter-subgranular fracture in Al-Li alloys when tested in the S-T orientation in air or vacuum make it difficult to readily detect H2 induced fracture based on straight forward changes in fractography; (2) the inherently low H2 diffusivity and solubility in Al alloys is further compounded by a native oxide which acts as a H2 permeation barrier; and (3) H2 effects are masked by dissolution assisted processes when mechanical testing is performed in aqueous solutions
Heat Capacity Mapping Mission
The Tasman Front was delineated by airborne expendable bathythermograph survey; and an Heat Capacity Mapping Mission (HCMM) IR image on the same day shows the same principal features as determined from ground-truth. It is clear that digital enhancement of HCMM images is necessary to map ocean surface temperatures and when done, the Tasman Front and other oceanographic features can be mapped by this method, even through considerable scattered cloud cover
Witnessing Entanglement of EPR States With Second-Order Interference
The separability of the continuous-variable EPR state can be tested with
Hanbury-Brown and Twiss type interference. The second-order visibility of such
interference can provide an experimental test of entanglement. It is shown that
time-resolved interference leads to the Hong, Ou and Mandel deep, that provides
a signature of quantum non-separability for pure and mixed EPR states. A
Hanbury-Brown and Twiss type witness operator can be constructed to test the
quantum nature of the EPR entanglement.Comment: 9 pages, 5 figure
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