558 research outputs found
Strong low-frequency quantum correlations from a four-wave mixing amplifier
We show that a simple scheme based on nondegenerate four-wave mixing in a hot
atomic vapor behaves like a near-perfect phase-insensitive optical amplifier,
which can generate bright twin beams with a measured quantum noise reduction in
the intensity difference of more than 8 dB, close to the best optical
parametric amplifiers and oscillators. The absence of a cavity makes the system
immune to external perturbations, and the strong quantum noise reduction is
observed over a large frequency range.Comment: 4 pages, 4 figures. Major rewrite of the previous version. New
experimental results and further analysi
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
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
Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas
By driving photoassociation transitions we form electronically excited
molecules (Na) from ultra-cold (50-300 K) Na atoms. Using a second
laser to drive transitions from the excited state to a level in the molecular
ground state, we are able to split the photoassociation line and observe
features with a width smaller than the natural linewidth of the excited
molecular state. The quantum interference which gives rise to this effect is
analogous to that which leads to electromagnetically induced transparency in
three level atomic systems, but here one of the ground states is a
pair of free atoms while the other is a bound molecule. The linewidth is
limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 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
Trapping of Neutral Rubidium with a Macroscopic Three-Phase Electric Trap
We trap neutral ground-state rubidium atoms in a macroscopic trap based on
purely electric fields. For this, three electrostatic field configurations are
alternated in a periodic manner. The rubidium is precooled in a magneto-optical
trap, transferred into a magnetic trap and then translated into the electric
trap. The electric trap consists of six rod-shaped electrodes in cubic
arrangement, giving ample optical access. Up to 10^5 atoms have been trapped
with an initial temperature of around 20 microkelvin in the three-phase
electric trap. The observations are in good agreement with detailed numerical
simulations.Comment: 4 pages, 4 figure
Coulomb crystallization in expanding laser-cooled neutral plasmas
We present long-time simulations of expanding ultracold neutral plasmas,
including a full treatment of the strongly coupled ion dynamics. Thereby, the
relaxation dynamics of the expanding laser-cooled plasma is studied, taking
into account elastic as well as inelastic collisions. It is demonstrated that,
depending on the initial conditions, the ionic component of the plasma may
exhibit short-range order or even a superimposed long-range order resulting in
concentric ion shells. In contrast to ionic plasmas confined in traps, the
shell structures are built up from the center of the plasma cloud rather than
from the periphery
Dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor
We present an analysis of the dynamics of a nanomechanical resonator coupled
to a superconducting single electron transistor (SSET) in the vicinity of the
Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP)
resonances. For weak coupling and wide separation of dynamical timescales, we
find that for either superconducting resonance the dynamics of the resonator is
given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an
equilibrium heat bath, characterised by an effective temperature, which also
damps the resonator and renormalizes its frequency. Depending on the gate and
drain-source voltage bias points with respect to the superconducting resonance,
the SSET can also give rise to an instability in the mechanical resonator
marked by negative damping and temperature within the appropriate Fokker-Planck
equation. Furthermore, sufficiently close to a resonance, we find that the
Fokker-Planck description breaks down. We also point out that there is a close
analogy between coupling a nanomechanical resonator to a SSET in the vicinity
of the JQP resonance and Doppler cooling of atoms by means of lasers
Spinor dynamics in an antiferromagnetic spin-1 thermal Bose gas
We present experimental observations of coherent spin-population oscillations
in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population
oscillations in a multi-spatial-mode thermal gas have the same behavior as
those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein
condensate. We demonstrate this by showing that the two situations are
described by the same dynamical equations, with a factor of two change in the
spin-dependent interaction coefficient, which results from the change to
particles with distinguishable momentum states in the thermal gas. We compare
this theory to the measured spin population evolution after times up to a few
hundreds of ms, finding quantitative agreement with the amplitude and period.
We also measure the damping time of the oscillations as a function of magnetic
field.Comment: 5 pages, 3 figure
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