2,564 research outputs found
Tuning the scattering length with an optically induced Feshbach resonance
We demonstrate optical tuning of the scattering length in a Bose-Einstein
condensate as predicted by Fedichev {\em et al.} [Phys. Rev. Lett. {\bf 77},
2913 (1996)]. In our experiment atoms in a Rb condensate are exposed to
laser light which is tuned close to the transition frequency to an excited
molecular state. By controlling the power and detuning of the laser beam we can
change the atomic scattering length over a wide range. In view of laser-driven
atomic losses we use Bragg spectroscopy as a fast method to measure the
scattering length of the atoms.Comment: submitted to PRL, 5 pages, 5 figure
A hatvani SzĂ©chenyi Zsigmond VadĂĄszati MĂșzeum = The SzĂ©chenyi Zsigmond Hunting Museum in Hatvan
Th e opening of the Széchenyi Zsigmond Hunting Museum in the baroque Grassalkovich Mansion in Hatvan, Hungary was the realisation of a 100-year-old dream. Th e Hungarian hunting and fi shing culture and traditions are shown through nine exhibitions on three floors: game species of the Carpathian Basin, clothing, music, art pieces etc. related to or inspired by hunting.
Th e museum uniquely combines traditional elements like display cabinets with interactive computers, which allow the visitor a playful learning experience and thorough understanding of
the role of hunting in our modern, mostly urbanised society. In the park of the castle, in two modern buildings, the so-called âAdventure Placeâ provides the chance for everyone to try shooting with laser guns and bowhunting, which gives an insight into the practices of modern hunting. With 9 figures
Comment on "Conductance fluctuations in mesoscopic normal-metal/superconductor samples"
Recently, Hecker et al. [Phys. Rev. Lett. 79, 1547 (1997)] experimentally
studied magnetoconductance fluctuations in a mesoscopic Au wire connected to a
superconducting Nb contact. They claimed to have observed an enhancement of the
rms magnitude of these conductance fluctuations in the superconducting state
(rms(Gns)) relative to that in the normal state (rms(Gn)) by a factor of 2.8.
In this comment, we argue that the measured rms(Gns) is NOT significantly
enhanced compared to rms(Gn) when we correct for the presence of an incoherent
series resistance from the contacts, which is different when Nb is in the
superconducting or normal state.Comment: 1 pag
Coherent optical transfer of Feshbach molecules to a lower vibrational state
Using the technique of stimulated Raman adiabatic passage (STIRAP) we have
coherently transferred ultracold 87Rb2 Feshbach molecules into a more deeply
bound vibrational quantum level. Our measurements indicate a high transfer
efficiency of up to 87%. As the molecules are held in an optical lattice with
not more than a single molecule per lattice site, inelastic collisions between
the molecules are suppressed and we observe long molecular lifetimes of about 1
s. Using STIRAP we have created quantum superpositions of the two molecular
states and tested their coherence interferometrically. These results represent
an important step towards Bose-Einstein condensation (BEC) of molecules in the
vibrational ground state.Comment: 4 pages, 5 figure
Repulsively bound atom pairs: Overview, Simulations and Links
We review the basic physics of repulsively bound atom pairs in an optical
lattice, which were recently observed in the laboratory, including the theory
and the experimental implementation. We also briefly discuss related many-body
numerical simulations, in which time-dependent Density Matrix Renormalisation
Group (DMRG) methods are used to model the many-body physics of a collection of
interacting pairs, and give a comparison of the single-particle quasimomentum
distribution measured in the experiment and results from these simulations. We
then give a short discussion of how these repulsively bound pairs relate to
bound states in some other physical systems.Comment: 7 pages, 3 figures, Proceedings of ICAP-2006 (Innsbruck
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Cruising through molecular bound state manifolds with radio frequency
The emerging field of ultracold molecules with their rich internal structure
is currently attracting a lot of interest. Various methods have been developed
to produce ultracold molecules in pre-set quantum states. For future
experiments it will be important to efficiently transfer these molecules from
their initial quantum state to other quantum states of interest. Optical Raman
schemes are excellent tools for transfer, but can be involved in terms of
equipment, laser stabilization and finding the right transitions. Here we
demonstrate a very general and simple way for transfer of molecules from one
quantum state to a neighboring quantum state with better than 99% efficiency.
The scheme is based on Zeeman tuning the molecular state to avoided level
crossings where radio-frequency transitions can then be carried out. By
repeating this process at different crossings, molecules can be successively
transported through a large manifold of quantum states. As an important
spin-off of our experiments, we demonstrate a high-precision spectroscopy
method for investigating level crossings.Comment: 5 pages, 5 figures, submitted for publicatio
Collective oscillations of a Fermi gas in the unitarity limit: Temperature effects and the role of pair correlations
We present detailed measurements of the frequency and damping of three
different collective modes in an ultracold trapped Fermi gas of Li atoms
with resonantly tuned interactions. The measurements are carried out over a
wide range of temperatures. We focus on the unitarity limit, where the
scattering length is much greater than all other relevant length scales. The
results are compared to theoretical calculations that take into account Pauli
blocking and pair correlations in the normal state above the critical
temperature for superfluidity. We show that these two effects nearly compensate
each other and the behavior of the gas is close to the one of a classical gas.Comment: 8 pages, 5 figure
Pure Gas of Optically Trapped Molecules Created from Fermionic Atoms
We report on the production of a pure sample of up to 3x10^5 optically
trapped molecules from a Fermi gas of 6Li atoms. The dimers are formed by
three-body recombination near a Feshbach resonance. For purification a
Stern-Gerlach selection technique is used that efficiently removes all trapped
atoms from the atom-molecule mixture. The behavior of the purified molecular
sample shows a striking dependence on the applied magnetic field. For very
weakly bound molecules near the Feshbach resonance, the gas exhibits a
remarkable stability with respect to collisional decay.Comment: 4 pages, 5 figure
Atom-molecule dark states in a Bose-Einstein condensate
We have created a dark quantum superposition state of a Rb Bose-Einstein
condensate (BEC) and a degenerate gas of Rb ground state molecules in a
specific ro-vibrational state using two-color photoassociation. As a signature
for the decoupling of this coherent atom-molecule gas from the light field we
observe a striking suppression of photoassociation loss. In our experiment the
maximal molecule population in the dark state is limited to about 100 Rb
molecules due to laser induced decay. The experimental findings can be well
described by a simple three mode model.Comment: 4 pages, 6 figure
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