276 research outputs found
Scattering of plasmons at the intersection of two metallic nanotubes: Implications for tunnelling
We study theoretically the plasmon scattering at the intersection of two
metallic carbon nanotubes. We demonstrate that for a small angle of crossing,
, the transmission coefficient is an oscillatory function of
, where is the interaction parameter of the Luttinger
liquid in an individual nanotube. We calculate the tunnel density of states,
, as a function of energy, , and distance, , from the
intersection. In contrast to a single nanotube, we find that, in the geometry
of crossed nanotubes, conventional "rapid" oscillations in due
to the plasmon scattering acquire an aperiodic "slow-breathing" envelope which
has nodes.Comment: 4 pages, 2 figures (revised version
Triplet s-wave resonance in 6Li collisions and scattering lengths of 6Li and 7Li
Journal ArticleThe triplet s-wave scattering length of 6Li is determined using two-photon photoassociative spectroscopy of the diatomic α 3Σu+ state of 6Li2. The measured binding energy of the highest-lying bound state, combined with knowledge of the potential, determines the s-wave scattering length to be -2160±250)α0, where α0 is the Bohr radius. This extraordinarily large scattering length signifies a near-threshold resonance. A complete table of singlet and triplet scattering lengths for collisions involving 6Li and 7Li determined from this and our previous spectroscopic investigations is given
Singlet s-wave scattering lengths of 6Li and 7Li
Journal ArticlePhotoassociation of ultracold lithium atoms into bound vibrational levels of the A 1Σu+ excited state is used to probe the X1Σg+ ground-state interaction potential of 6Li2 and 7Li2 . It had been predicted that the s-wave photoassociation signal strength would pass through a minimum as a function of vibrational level for positive s-wave scattering length. We report the observation of this novel effect, and use the location of the minimum to precisely determine the singlet s-wave scattering length for both isotopes. The sensitivity of this technique is demonstrated by distinguishing the minima for collisions involving 7Li atoms in different hyperfine states
The need of continuous focus on improved mentoring of trainees and young investigators in the field of andrology: highlights of current programs and opportunities for the future
Photoassociation of sodium in a Bose-Einstein condensate
We report on the formation of ultra-cold Na molecules using single-photon
photoassociation of a Bose-Einstein condensate. The photoassociation rate,
linewidth and light shift of the J=1, vibrational level of the
\mterm{A}{1}{+}{u} molecular bound state have been measured. We find that the
photoassociation rate constant increases linearly with intensity, even where it
is predicted that many-body effects might limit the rate. Our observations are
everywhere in good agreement with a two-body theory having no free parameters.Comment: Fixes to the figures and references. Just the normal human stupidity
type stuff, nothing Earth-shatterin
Spectroscopic Temperature Determination of Degenerate Fermi Gases
We suggest a simple method for measuring the temperature of ultra-cold gases
made of fermions. We show that by using a two-photon Raman probe, it is
possible to obtain lineshapes which reveal properties of the degenerate sample,
notably its temperature . The proposed method could be used with identical
fermions in different hyperfine states interacting via s-wave scattering or
identical fermions in the same hyperfine state via p-wave scattering. We
illustrate the applicability of the method in realistic conditions for Li
prepared in two different hyperfine states. We find that temperatures down to
0.05 can be determined by this {\it in-situ} method.Comment: 7 pages, 4 figures, Revtex
Mean-field analysis of collapsing and exploding Bose-Einstein condensates
The dynamics of collapsing and exploding trapped Bose-Einstein condensat es
caused by a sudden switch of interactions from repulsive to attractive a re
studied by numerically integrating the Gross-Pitaevskii equation with atomic
loss for an axially symmetric trap. We investigate the decay rate of
condensates and the phenomena of bursts and jets of atoms, and compare our
results with those of the experiments performed by E. A. Donley {\it et al.}
[Nature {\bf 412}, 295 (2001)]. Our study suggests that the condensate decay
and the burst production is due to local intermittent implosions in the
condensate, and that atomic clouds of bursts and jets are coherent. We also
predict nonlinear pattern formation caused by the density instability of
attractive condensates.Comment: 7 pages, 8 figures, axi-symmetric results are adde
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
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
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
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