5,983 research outputs found
Optical Lenses for Atomic Beams
Superpositions of paraxial laser beam modes to generate atom-optical lenses
based on the optical dipole force are investigated theoretically. Thin, wide,
parabolic, cylindrical and circular atom lenses with numerical apertures much
greater than those reported in the literature to date can be synthesized. This
superposition approach promises to make high quality atom beam imaging and
nano-deposition feasible.Comment: 10 figure
Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County
This study examines the nature of water-soluble organic aerosol measured in Pasadena, CA, under typical conditions and under the influence of a large wildfire (the 2009 Station Fire). During non-fire periods, water-soluble organic carbon (WSOC) variability was driven by photochemical production processes and sea breeze transport, resulting in an average diurnal cycle with a maximum at 15:00 local time (up to 4.9 μg C m^(−3)). During the Station Fire, primary production was a key formation mechanism for WSOC. High concentrations of WSOC (up to 41 μg C m^(−3)) in smoke plumes advected to the site in the morning hours were tightly correlated with nitrate and chloride, numerous aerosol mass spectrometer (AMS) organic mass spectral markers, and total non-refractory organic mass. Processed residual smoke was transported to the measurement site by the sea breeze later in the day, leading to higher afternoon WSOC levels than on non-fire days. Parameters representing higher degrees of oxidation of organics, including the ratios of the organic metrics m/z 44:m/z 57 and m/z 44:m/z 43, were elevated in those air masses. Intercomparisons of relative amounts of WSOC, organics, m/z 44, and m/z 43 show that the fraction of WSOC comprising acid-oxygenates increased as a function of photochemical aging owing to the conversion of aliphatic and non-acid oxygenated organics to more acid-like organics. The contribution of water-soluble organic species to the organic mass budget (10th–90th percentile values) ranged between 27 %–72 % and 27 %–68 % during fire and non-fire periods, respectively. The seasonal incidence of wildfires in the Los Angeles Basin greatly enhances the importance of water-soluble organics, which has implications for the radiative and hygroscopic properties of the regional aerosol
Probing -Spin Correlations in Optical Lattices
We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to -spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.Comment: 7 pages, 4 figure
Compression of Atomic Phase Space Using an Asymmetric One-Way Barrier
We show how to construct asymmetric optical barriers for atoms. These
barriers can be used to compress phase space of a sample by creating a confined
region in space where atoms can accumulate with heating at the single photon
recoil level. We illustrate our method with a simple two-level model and then
show how it can be applied to more realistic multi-level atoms
Universality and Critical Behavior at the Mott transition
We report conductivity measurements of Cr-doped V2O3 using a variable
pressure technique. The critical behavior of the conductivity near the
Mott-insulator to metal critical endpoint is investigated in detail as a
function of pressure and temperature. The critical exponents are determined, as
well as the scaling function associated with the equation of state. The
universal properties of a liquid-gas transition are found. This is potentially
a generic description of the Mott critical endpoint in correlated electron
materials.Comment: 3 figure
Andreev reflection in bosonic condensates
We study the bosonic analog of Andreev reflection at a normal-superfluid
interface where the superfluid is a boson condensate. We model the normal
region as a zone where nonlinear effects can be neglected. Against the
background of a decaying condensate, we identify a novel contribution to the
current of reflected atoms. The group velocity of this Andreev reflected
component differs from that of the normally reflected one. For a
three-dimensional planar or two-dimensional linear interface Andreev reflection
is neither specular nor conjugate.Comment: 5 pages, 3 figures. Text revise
Atom cooling by non-adiabatic expansion
Motivated by the recent discovery that a reflecting wall moving with a
square-root in time trajectory behaves as a universal stopper of classical
particles regardless of their initial velocities, we compare linear in time and
square-root in time expansions of a box to achieve efficient atom cooling. For
the quantum single-atom wavefunctions studied the square-root in time expansion
presents important advantages: asymptotically it leads to zero average energy
whereas any linear in time (constant box-wall velocity) expansion leaves a
non-zero residual energy, except in the limit of an infinitely slow expansion.
For finite final times and box lengths we set a number of bounds and cooling
principles which again confirm the superior performance of the square-root in
time expansion, even more clearly for increasing excitation of the initial
state. Breakdown of adiabaticity is generally fatal for cooling with the linear
expansion but not so with the square-root expansion.Comment: 4 pages, 4 figure
Laser cooling of new atomic and molecular species with ultrafast pulses
We propose a new laser cooling method for atomic species whose level
structure makes traditional laser cooling difficult. For instance, laser
cooling of hydrogen requires single-frequency vacuum-ultraviolet light, while
multielectron atoms need single-frequency light at many widely separated
frequencies. These restrictions can be eased by laser cooling on two-photon
transitions with ultrafast pulse trains. Laser cooling of hydrogen,
antihydrogen, and many other species appears feasible, and extension of the
technique to molecules may be possible.Comment: revision of quant-ph/0306099, submitted to PR
Three-Way Entanglement and Three-Qubit Phase Gate Based on a Coherent Six-Level Atomic System
We analyze the nonlinear optical response of a six-level atomic system under
a configuration of electromagnetically induced transparency. The giant
fifth-order nonlinearity generated in such a system with a relatively large
cross-phase modulation effect can produce efficient three-way entanglement and
may be used for realizing a three-qubit quantum phase gate. We demonstrate that
such phase gate can be transferred to a Toffoli gate, facilitating practical
applications in quantum information and computation.Comment: 10 pages, 2 figure
NonClassicality Criteria in Multiport Interferometry
Interference lies at the heart of the behavior of classical and quantum
light. It is thus crucial to understand the boundaries between which
interference patterns can be explained by a classical electromagnetic
description of light and which, on the other hand, can only be understood with
a proper quantum mechanical approach. While the case of two-mode interference
has received a lot of attention, the multimode case has not yet been fully
explored. Here we study a general scenario of intensity interferometry: we
derive a bound on the average correlations between pairs of output intensities
for the classical wavelike model of light, and we show how it can be violated
in a quantum framework. As a consequence, this violation acts as a
nonclassicality witness, able to detect the presence of sources with
sub-Poissonian photon-number statistics. We also develop a criterion that can
certify the impossibility of dividing a given interferometer into two
independent subblocks.Comment: 5 + 3 pages, published versio
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