22 research outputs found
High-precision spectroscopy of the forbidden 2 3S1 - 2 1P1 transition in quantum degenerate metastable helium
We have measured the forbidden 2 3S1 - 2 1P1 transition at 887 nm in a
quantum degenerate gas of metastable He-4 atoms confined in an optical dipole
trap. The determined transition frequency is 338 133 594.4 (0.5) MHz, from
which we obtain an ionization energy of the 2 1P1 state of 814 709 148.6 (0.5)
MHz. This ionization energy is in disagreement by > 3 sigma with the most
accurate quantum electrodynamics (QED) calculations available. Our measurements
also provide a new determination of the lifetime of the 2 1P1 state of 0.551
(0.004)stat (+ 0.013,- 0.000)syst ns, which is the most accurate determination
to date and in excellent agreement with theory.Comment: 10 pages, 13 figures, paper includes supplemental information. Paper
submitted for revie
Quantum-State Controlled Penning Ionization Reactions between Ultracold Alkali and Metastable Helium Atoms
In an ultracold, optically trapped mixture of Rb and metastable
triplet He atoms we have studied trap loss for different spin-state
combinations, for which interspecies Penning ionization is the main two-body
loss process. We observe long trapping lifetimes for the purely quartet
spin-state combination, indicating strong suppression of Penning ionization
loss by at least two orders of magnitude. For the other spin-mixtures we
observe short lifetimes that depend linearly on the doublet character of the
entrance channel. We compare the extracted loss rate coefficient with recent
predictions of multichannel quantum-defect theory for reactive collisions
involving a strong exothermic loss channel and find near-universal loss for
doublet scattering. Our work demonstrates control of reactive collisions by
internal atomic state preparation.Comment: 5 pages, 5 figures + Supplemental Material
Theory of evaporative cooling with energy-dependent elastic scattering cross section and application to metastable helium
The kinetic theory of evaporative cooling developed by Luiten et al. [Phys.
Rev. A 53, 381 (1996)] is extended to include the dependence of the elastic
scattering cross section on collision energy. We introduce a simple
approximation by which the transition range between the low-temperature limit
and the unitarity limit is described as well. Applying the modified theory to
our measurements on evaporative cooling of metastable helium we find a
scattering length |a| = 10(5) nm
Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate in a hybrid trap
We have realized Bose-Einstein condensation (BEC) of 87Rb in the F=2, m_F=2
hyperfine substate in a hybrid trap, consisting of a quadrupole magnetic field
and a single optical dipole beam. The symmetry axis of the quadrupole magnetic
trap coincides with the optical beam axis, which gives stronger axial
confinement than previous hybrid traps. After loading 2x10^6 atoms at 14 muK
from a quadrupole magnetic trap into the hybrid trap, we perform efficient
forced evaporation and reach the onset of BEC at a temperature of 0.5 muK and
with 4x10^5 atoms. We also obtain thermal clouds of 1x10^6 atoms below 1 muK in
a pure single beam optical dipole trap, by ramping down the magnetic field
gradient after evaporative cooling in the hybrid trap.Comment: 8 pages, 8 figures, improved on basis of referee comment
HYPERFINE-STRUCTURE IN THE 6SNH (1 = 5) RYDBERG SERIES OF BARIUM
The hyperfine structure in the odd-parity 6snh (9 ≤ n ≤ 40) Rydberg series of barium has been investigated, using a single cw ring dye laser and a beam of neutral atoms in the metastable 5
Effect of atomic transfer on the decay of a Bose-Einstein condensate
We present a model describing the decay of a Bose-Einstein condensate, which
assumes the system to remain in thermal equilibrium during the decay. We show
that under this assumption transfer of atoms occurs from the condensate to the
thermal cloud enhancing the condensate decay rate
Producing and Detecting Correlated atoms
We discuss experiments to produce and detect atom correlations in a
degenerate or nearly degenerate gas of neutral atoms. First we treat the atomic
analog of the celebrated Hanbury Brown Twiss experiment, in which atom
correlations result simply from interference effects without any atom
interactions.We have performed this experiment for both bosons and fermions.
Next we show how atom interactions produce correlated atoms using the atomic
analog of spontaneous four-wavemixing. Finally, we briefly mention experiments
on a one dimensional gas on an atom chip in which correlation effects due to
both interference and interactions have been observed.Comment: to appear in conference proceedings "Atomic Physics 20
Cold and trapped metastable noble gases
We review experimental and theoretical work on cold, trapped metastable noble
gases. We em- phasize the aspects which distinguish work with these atoms from
the large body of work on cold, trapped atoms in general. These aspects include
detection techniques and collision processes unique to metastable atoms. We
describe several experiments exploiting these unique features in fields
including atom optics and statistical physics. We also discuss precision
measurements on these atoms including fine structure splittings, isotope
shifts, and atomic lifetimes