3,615 research outputs found
Bose-Einstein Condensation of Sr Through Sympathetic Cooling with Sr
We report Bose-Einstein condensation of Sr, which has a small,
negative s-wave scattering length (\,). We overcome the poor
evaporative cooling characteristics of this isotope by sympathetic cooling with
Sr atoms. Sr is effective in this role in spite of the fact that
it is a fermion because of the large ground state degeneracy arising from a
nuclear spin of , which reduces the impact of Pauli blocking of
collisions. We observe a limited number of atoms in the condensate
() that is consistent with the value of and the
optical dipole trap parameters.Comment: 4 pages, 4 figure
Degenerate Fermi Gas of Sr
We report quantum degeneracy in a gas of ultra-cold fermionic Sr
atoms. By evaporatively cooling a mixture of spin states in an optical dipole
trap for 10.5\,s, we obtain samples well into the degenerate regime with
. The main signature of degeneracy is a change in the
momentum distribution as measured by time-of-flight imaging, and we also
observe a decrease in evaporation efficiency below .Comment: 4 pages, 3 figure
Inelastic and elastic collision rates for triplet states of ultracold strontium
We report measurement of the inelastic and elastic collision rates for
^{88}Sr atoms in the (5s5p)^3P_0 state in a crossed-beam optical dipole trap.
This is the first measurement of ultracold collision properties of a ^3P_0
level in an alkaline-earth atom or atom with similar electronic structure.
Since the (5s5p)^3P_0 state is the lowest level of the triplet manifold, large
loss rates indicate the importance of principle-quantum-number-changing
collisions at short range. We also provide an estimate of the collisional loss
rates for the (5s5p){^3P_2} state.Comment: 4 pages 5 figure
Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p)3P2 - (5s4d)3D2 transition
We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms
using the (5s5p)3P2 - (5s4d)3D2 transition. Atom number in a magneto-optical
trap is enhanced by driving this transition because Sr atoms that have decayed
into the (5s5p)3P2 dark state are repumped back into the (5s2)1S0 ground state.
Spectroscopy of 84Sr, 86Sr, 87Sr, and 88Sr improves the value of the (5s5p)3P2
- (5s4d)3D2 transition frequency for 88Sr and determines the isotope shifts for
the transition.Comment: 4 pages, 5 figure
Two-photon photoassociative spectroscopy of ultracold 88-Sr
We present results from two-photon photoassociative spectroscopy of the
least-bound vibrational level of the X state of the Sr
dimer. Measurement of the binding energy allows us to determine the s-wave
scattering length, . For the intermediate state, we use a
bound level on the metastable - potential, which provides large
Franck-Condon transition factors and narrow one-photon photoassociative lines
that are advantageous for observing quantum-optical effects such as
Autler-Townes resonance splittings.Comment: 9 pages, 9 figure
Bose-Einstein Condensation of 84Sr
We report Bose-Einstein condensation of Sr84 in an optical dipole trap. Efficient laser cooling on the narrow intercombination line and an ideal s-wave scattering length allow the creation of large condensates (N0∼3×105) even though the natural abundance of this isotope is only 0.6%. Condensation is heralded by the emergence of a low-velocity component in time-of-flight images
Numerical modeling of collisional dynamics of Sr in an optical dipole trap
We describe a model of inelastic and elastic collisional dynamics of atoms in an optical dipole trap that utilizes numerical evaluation of statistical mechanical quantities and numerical solution of equations for the evolution of number and temperature of trapped atoms. It can be used for traps that possess little spatial symmetry and when the ratio of trap depth to sample temperature is relatively small. We compare simulation results with experiments on Sr88 and Sr84, which have well-characterized collisional properties
An SU(N) Mott insulator of an atomic Fermi gas realized by large-spin Pomeranchuk cooling
The Hubbard model, containing only the minimum ingredients of nearest
neighbor hopping and on-site interaction for correlated electrons, has
succeeded in accounting for diverse phenomena observed in solid-state
materials. One of the interesting extensions is to enlarge its spin symmetry to
SU(N>2), which is closely related to systems with orbital degeneracy. Here we
report a successful formation of the SU(6) symmetric Mott insulator state with
an atomic Fermi gas of ytterbium (173Yb) in a three-dimensional optical
lattice. Besides the suppression of compressibility and the existence of charge
excitation gap which characterize a Mott insulating phase, we reveal an
important difference between the cases of SU(6) and SU(2) in the achievable
temperature as the consequence of different entropy carried by an isolated
spin. This is analogous to Pomeranchuk cooling in solid 3He and will be helpful
for investigating exotic quantum phases of SU(N) Hubbard system at extremely
low temperatures.Comment: 20 pages, 6 figures, to appear in Nature Physic
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
- …