2,121 research outputs found
Confinement effects in a guided-wave interferometer with millimeter-scale arm separation
Guided-wave atom interferometers measure interference effects using atoms
held in a confining potential. In one common implementation, the confinement is
primarily two-dimensional, and the atoms move along the nearly free dimension
under the influence of an off-resonant standing wave laser beam. In this
configuration, residual confinement along the nominally free axis can introduce
a phase gradient to the atoms that limits the arm separation of the
interferometer. We experimentally investigate this effect in detail, and show
that it can be alleviated by having the atoms undergo a more symmetric motion
in the guide. This can be achieved by either using additional laser pulses or
by allowing the atoms to freely oscillate in the potential. Using these
techniques, we demonstrate interferometer measurement times up to 72 ms and arm
separations up to 0.42 mm with a well controlled phase, or times of 0.91 s and
separations of 1.7 mm with an uncontrolled phase.Comment: 14 pages, 6 figure
Stabilizing an Attractive Bose-Einstein Condensate by Driving a Surface Collective Mode
Bose-Einstein condensates of Li have been limited in number due to
attractive interatomic interactions. Beyond this number, the condensate
undergoes collective collapse. We study theoretically the effect of driving
low-lying collective modes of the condensate by a weak asymmetric sinusoidally
time-dependent field. We find that driving the radial breathing mode further
destabilizes the condensate, while excitation of the quadrupolar surface mode
causes the condensate to become more stable by imparting quasi-angular momentum
to it. We show that a significantly larger number of atoms may occupy the
condensate, which can then be sustained almost indefinitely. All effects are
predicted to be clearly visible in experiments and efforts are under way for
their experimental realization.Comment: 4 ReVTeX pages + 2 postscript figure
A Time-Orbiting Potential Trap for Bose-Einstein Condensate Interferometry
We describe a novel atom trap for Bose-Einstein condensates of 87Rb to be
used in atom interferometry experiments. The trap is based on a time-orbiting
potential waveguide. It supports the atoms against gravity while providing weak
confinement to minimize interaction effects. We observe harmonic oscillation
frequencies omega_x, omega_y, omega_z as low as 2 pi times (6.0,1.2,3.3) Hz. Up
to 2 times 10^4 condensate atoms have been loaded into the trap, at estimated
temperatures as low as 850 pK. We anticipate that interferometer measurement
times of 1 s or more should be achievable in this device.Comment: 9 pages, 3 figure
Explosion of a collapsing Bose-Einstein condensate
We show that elastic collisions between atoms in a Bose-Einstein condensate
with attractive interactions lead to an explosion that ejects a large fraction
of the collapsing condensate. We study variationally the dynamics of this
explosion and find excellent agreement with recent experiments on magnetically
trapped Rubidium-85. We also determine the energy and angular distribution of
the ejected atoms during the collapse.Comment: Four pages of ReVTeX and five postscript figure
Instantons and radial excitations in attractive Bose-Einstein condensates
Imaginary- and real-time versions of an equation for the condensate density
are presented which describe dynamics and decay of any spherical Bose-Einstein
condensate (BEC) within the mean field appraoch. We obtain quantized energies
of collective finite amplitude radial oscillations and exact numerical
instanton solutions which describe quantum tunneling from both the metastable
and radially excited states of the BEC of 7Li atoms. The mass parameter for the
radial motion is found different from the gaussian value assumed hitherto, but
the effect of this difference on decay exponents is small. The collective
breathing states form slightly compressed harmonic spectrum, n=4 state lying
lower than the second Bogolyubov (small amplitude) mode. The decay of these
states, if excited, may simulate a shorter than true lifetime of the metastable
state. By scaling arguments, results extend to other attractive BEC-s.Comment: 6 pages, 3 figure
Intermittent implosion and pattern formation of trapped Bose-Einstein condensates with attractive interaction
The collapsing dynamics of a trapped Bose-Einstein condensate (BEC) with
attractive interaction are revealed to exhibit two previously unknown
phenomena. During the collapse, BEC undergoes a series of rapid implosions that
occur {\it intermittently} within a very small region. When the sign of the
interaction is suddenly switched from repulsive to attractive, e.g., by the
Feshbach resonance, density fluctuations grow to form various patterns such as
a shell structure.Comment: 5 pages, 2 figures, RevTeX, epsf.sty, corrected loss rate
Heating of trapped ions from the quantum ground state
We have investigated motional heating of laser-cooled 9Be+ ions held in
radio-frequency (Paul) traps. We have measured heating rates in a variety of
traps with different geometries, electrode materials, and characteristic sizes.
The results show that heating is due to electric-field noise from the trap
electrodes which exerts a stochastic fluctuating force on the ion. The scaling
of the heating rate with trap size is much stronger than that expected from a
spatially uniform noise source on the electrodes (such as Johnson noise from
external circuits), indicating that a microscopic uncorrelated noise source on
the electrodes (such as fluctuating patch-potential fields) is a more likely
candidate for the source of heating.Comment: With minor changes. 24 pages, including 7 figures. Submitted by Phys.
Rev.
Power laws and collapsing dynamics of a trapped Bose-Einstein condensate with attractive interactions
The critical behavior of collective modes and the collapsing dynamics of
trapped Bose-Einstein condensates with attractive interactions are studied
analytically and numerically. The time scales of these dynamics both below and
above the critical point of the collapse are found to obey power laws with a
single parameter of N/N_c - 1, where N is the number of condensate atoms and
N_c is the critical number. The collapsing condensate eventually undergoes
rapid implosion, which occurs several times intermittently, and then the
implosion turns to an explosion. The release energy of the explosion is found
to be proportional to the square of the interaction strength, inversely
proportional to the three-body recombination rate, and independent of the
number of condensate atoms and the trap frequency.Comment: 9 pages, RevTeX, 7 figures, epsf.sty, corrected loss rate
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