669 research outputs found
Light forces in ultracold photoassociation
We study the time-resolved photoassociation of ultracold sodium in an optical
dipole trap. The photoassociation laser excites pairs of atoms to molecular
states of large total angular momentum at high intensities (above 20
kW/cm). Such transitions are generally suppressed at ultracold
temperatures by the centrifugal barriers for high partial waves. Time-resolved
ionization measurements reveal that the atoms are accelerated by the dipole
potential of the photoassociation beam. We change the collision energy by
varying the potential depth, and observe a strong variation of the
photoassociation rate. These results demonstrate the important role of light
forces in cw photoassociation at high intensities.Comment: 7 pages, 3 figure
Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate
We observe coherent spin oscillations in an antiferromagnetic spin-1
Bose-Einstein condensate of sodium. The variation of the spin oscillations with
magnetic field shows a clear signature of nonlinearity, in agreement with
theory, which also predicts anharmonic oscillations near a critical magnetic
field. Measurements of the magnetic phase diagram agree with predictions made
in the approximation of a single spatial mode. The oscillation period yields
the best measurement to date of the sodium spin-dependent interaction
coefficient, determining that the difference between the sodium spin-dependent
s-wave scattering lengths is Bohr radii.Comment: 5 pages, 2 figures. Changes: added reference, minor correction
All-optical generation and photoassociative probing of sodium Bose-Einstein condensates
We demonsatrate an all optical technique to evaporatively produce sodium
Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light
near 1060 nm, and a simple ramp of the intensity to force evaporation. In
addition, we introduce photoassociation as diagnostic of the trap loading
process, and show that it can be used to detect the onset of Bose-Einstein
condensation. Finally, we demonstrate the straightforward production of
multiple traps with condensates using this technique, and that some control
over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure
Ultraslow propagation of matched pulses by four-wave mixing in an atomic vapor
We have observed the ultraslow propagation of matched pulses in nondegenerate
four-wave mixing in a hot atomic vapor. Probe pulses as short as 70 ns can be
delayed by a tunable time of up to 40 ns with little broadening or distortion.
During the propagation, a probe pulse is amplified and generates a conjugate
pulse which is faster and separates from the probe pulse before getting locked
to it at a fixed delay. The precise timing of this process allows us to
determine the key coefficients of the susceptibility tensor. The presence of
gain in this system makes this system very interesting in the context of
all-optical information processing.Comment: 5 pages, 4 figure
Effects of a physiotherapy and occupational therapy intervention on mobility and activity in care home residents: a cluster randomised controlled trial
Objective To compare the clinical effectiveness of a programme of physiotherapy and occupational therapy with standard care in care home residents who have mobility limitations and are dependent in performing activities of daily living
Narrow Line Cooling: Finite Photon Recoil Dynamics
We present an extensive study of the unique thermal and mechanical dynamics
for narrow-line cooling on the 1S0 - 3P1 88Sr transition. For negative
detuning, trap dynamics reveal a transition from the semiclassical regime to
the photon-recoil-dominated quantum regime, yielding an absolute minima in the
equilibrium temperature below the single-photon recoil limit. For positive
detuning, the cloud divides into discrete momentum packets whose alignment
mimics lattice points on a face-centered-cubic crystal. This novel behavior
arises from velocity selection and "positive feedback" acceleration due to a
finite number of photon recoils. Cooling is achieved with blue-detuned light
around a velocity where gravity balances the radiative force.Comment: 4 pages, 3 figures, Phys. Rev. Lett., in pres
Properties of Two-Mode Quadrature Squeezing from Four-wave Mixing in Rubidium Vapor
We present a study of homodyne measurements of two-mode, vacuum-seeded,
quadrature-squeezed light generated by four-wave mixing in warm rubidium vapor.
Our results reveal that the vacuum squeezing can extend down to measurement
frequencies of less than 1 Hz, and the squeezing bandwidth, similar to the
seeded intensity-difference squeezing measured in this system, reaches up to
approximately 20 MHz for typical pump parameters. By dividing the squeezing
bandwidth into smaller frequency bins, we show that different sideband
frequencies represent independent sources of two-mode squeezing. Such frequency
bins may provide useful qumodes for quantum information processing experiments.
We also investigate the impact of group velocity delays on the correlations in
the system
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