29 research outputs found
Response to Comment on "Pairing and Phase Separation in a Polarized Fermi Gas"
Zwierlein and Ketterle rely on subjective arguments and fail to recognize
important differences in physical parameters between our experiment and theirs.
We stand by the conclusions of our original report
An acoustic analog to the dynamical Casimir effect in a Bose-Einstein condensate
We have realized an acoustic analog to the Dynamical Casimir effect. The
density of a trapped Bose-Einstein condensate is modulated by changing the trap
stiffness. We observe the creation of correlated excitations with equal and
opposite momenta, and show that for a well defined modulation frequency, the
frequency of the excitations is half that of the trap modulation frequency.Comment: Includes supplemental informatio
Sub-Poissonian number differences in four-wave mixing of matter waves
We demonstrate sub-Poissonian number differences in four-wave mixing of
Bose-Einstein condensates of metastable helium. The collision between two
Bose-Einstein condensates produces a scattering halo populated by pairs of
atoms of opposing velocities, which we divide into several symmetric zones. We
show that the atom number difference for opposing zones has sub-Poissonian
noise fluctuations whereas that of nonopposing zones is well described by shot
noise. The atom pairs produced in a dual number state are well adapted to sub
shot-noise interferometry and studies of Einstein-Podolsky-Rosen-type
nonlocality tests.Comment: 4 pages, 3 figure
Pairing and Phase Separation in a Polarized Fermi Gas
We report the observation of a pairing in a number polarized two-component
gas of atomic fermions. Beyond a critical polarization, the gas separates into
a superfluid paired core surrounded by a shell of normal unpaired fermions. The
critical polarization diminishes with decreasing attractive interaction. We
also measure the parameter \beta = 0.54 (5) describing the universal energy of
a strongly interacting Fermi gas, and find good agreement with most recent
theory. These results are relevant to predictions of exotic new phases of quark
matter and of strongly magnetized superconductors
Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics
We investigate the atom-optical analog of degenerate four-wave mixing of
photons by colliding two Bose-Einstein condensates (BECs) of metastable helium
and measuring the resulting momentum distribution of the scattered atoms with a
time and space resolved detector. For the case of photons, phase matching
conditions completely define the final state of the system, and in the case of
two colliding BECs, simple analogy implies a spherical momentum distribution of
scattered atoms. We find, however, that the final momenta of the scattered
atoms instead lie on an ellipsoid whose radii are smaller than the initial
collision momentum. Numerical and analytical calculations agree well with the
measurements, and reveal the interplay between many-body effects, mean-field
interaction, and the anisotropy of the source condensate
Conversion of an Atomic Fermi Gas to a Long-Lived Molecular Bose Gas
We have converted an ultracold Fermi gas of Li atoms into an ultracold
gas of Li molecules by adiabatic passage through a Feshbach resonance.
Approximately molecules in the least-bound, ,
vibrational level of the X singlet state are produced with an
efficiency of 50%. The molecules remain confined in an optical trap for times
of up to 1 s before we dissociate them by a reverse adiabatic sweep.Comment: Accepted for publication in Phys. Rev. Letter
Spin-Imbalance in a One-Dimensional Fermi Gas
Superconductivity and magnetism generally do not coexist. Changing the
relative number of up and down spin electrons disrupts the basic mechanism of
superconductivity, where atoms of opposite momentum and spin form Cooper pairs.
Nearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an
exotic pairing mechanism (FFLO) where magnetism is accommodated by formation of
pairs with finite momentum. Despite intense theoretical and experimental
efforts, however, polarized superconductivity remains largely elusive. Here we
report experimental measurements of density profiles of a two spin mixture of
ultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system
analogous to electrons in 1D wires. At finite spin imbalance, the system phase
separates with an inverted phase profile in comparison to the three-dimensional
case. In 1D we find a partially polarized core surrounded by wings composed of
either a completely paired BCS superfluid or a fully polarized Fermi gas,
depending on the degree of polarization. Our observations are in quantitative
agreement with theoretical calculations in which the partially polarized phase
is found to be a 1D analogue of the FFLO state. This study demonstrates how
ultracold atomic gases in 1D may be used to create non-trivial new phases of
matter, and also paves the way for direct observation and further study of the
FFLO phase.Comment: 30 pages, 7 figure
Formation and Propagation of Matter Wave Soliton Trains
Attraction between atoms in a Bose-Einstein-Condensate renders the condensate
unstable to collapse. Confinement in an atom trap, however, can stabilize the
condensate for a limited number of atoms, as was observed with 7Li, but beyond
this number, the condensate collapses. Attractive condensates constrained to
one-dimensional motion are predicted to form stable solitons for which the
attractive interactions exactly compensate for the wave packet dispersion. Here
we report the formation or bright solitons of 7Li atoms created in a quasi-1D
optical trap. The solitons are created from a stable Bose-Einstein condensate
by magnetically tuning the interactions from repulsive to attractive. We
observe a soliton train, containing many solitons. The solitons are set in
motion by offsetting the optical potential and are observed to propagate in the
potential for many oscillatory cycles without spreading. Repulsive interactions
between neighboring solitons are inferred from their motion
Effects of fluoxetine on functional outcomes after acute stroke (FOCUS): a pragmatic, double-blind, randomised, controlled trial
Background
Results of small trials indicate that fluoxetine might improve functional outcomes after stroke. The FOCUS trial aimed to provide a precise estimate of these effects.
Methods
FOCUS was a pragmatic, multicentre, parallel group, double-blind, randomised, placebo-controlled trial done at 103 hospitals in the UK. Patients were eligible if they were aged 18 years or older, had a clinical stroke diagnosis, were enrolled and randomly assigned between 2 days and 15 days after onset, and had focal neurological deficits. Patients were randomly allocated fluoxetine 20 mg or matching placebo orally once daily for 6 months via a web-based system by use of a minimisation algorithm. The primary outcome was functional status, measured with the modified Rankin Scale (mRS), at 6 months. Patients, carers, health-care staff, and the trial team were masked to treatment allocation. Functional status was assessed at 6 months and 12 months after randomisation. Patients were analysed according to their treatment allocation. This trial is registered with the ISRCTN registry, number ISRCTN83290762.
Findings
Between Sept 10, 2012, and March 31, 2017, 3127 patients were recruited. 1564 patients were allocated fluoxetine and 1563 allocated placebo. mRS data at 6 months were available for 1553 (99·3%) patients in each treatment group. The distribution across mRS categories at 6 months was similar in the fluoxetine and placebo groups (common odds ratio adjusted for minimisation variables 0·951 [95% CI 0·839–1·079]; p=0·439). Patients allocated fluoxetine were less likely than those allocated placebo to develop new depression by 6 months (210 [13·43%] patients vs 269 [17·21%]; difference 3·78% [95% CI 1·26–6·30]; p=0·0033), but they had more bone fractures (45 [2·88%] vs 23 [1·47%]; difference 1·41% [95% CI 0·38–2·43]; p=0·0070). There were no significant differences in any other event at 6 or 12 months.
Interpretation
Fluoxetine 20 mg given daily for 6 months after acute stroke does not seem to improve functional outcomes. Although the treatment reduced the occurrence of depression, it increased the frequency of bone fractures. These results do not support the routine use of fluoxetine either for the prevention of post-stroke depression or to promote recovery of function.
Funding
UK Stroke Association and NIHR Health Technology Assessment Programme