68 research outputs found
Bose gas: Theory and Experiment
For many years, He typified Bose-Einstein superfluids, but recent
advances in dilute ultra-cold alkali-metal gases have provided new neutral
superfluids that are particularly tractable because the system is dilute. This
chapter starts with a brief review of the physics of superfluid He,
followed by the basic ideas of Bose-Einstein condensation (BEC), first for an
ideal Bose gas and then considering the effect of interparticle interactions,
including time-dependent phenomena. Extensions to more exotic condensates
include magnetic dipolar gases, mixtures of two components, and spinor
condensates that require a focused infrared laser for trapping of all the
various hyperfine magnetic states in a particular hyperfine manifold of
states. With an applied rotation, the trapped BECs nucleate quantized
vortices. Recent theory and experiment have shown that laser coupling fields
can mimic the effect of rotation. The resulting synthetic gauge fields have
produced vortices in a nonrotating condensate
Ultracold atoms in multiple-radiofrequency dressed adiabatic potentials
We present the first experimental demonstration of a multiple-radiofrequency
dressed potential for the configurable magnetic confinement of ultracold atoms.
We load cold Rb atoms into a double well potential with an adjustable
barrier height, formed by three radiofrequencies applied to atoms in a static
quadrupole magnetic field. Our multiple-radiofrequency approach gives precise
control over the double well characteristics, including the depth of individual
wells and the height of the barrier, and enables reliable transfer of atoms
between the available trapping geometries. We have characterised the
multiple-radiofrequency dressed system using radiofrequency spectroscopy,
finding good agreement with the eigenvalues numerically calculated using
Floquet theory. This method creates trapping potentials that can be
reconfigured by changing the amplitudes, polarizations and frequencies of the
applied dressing fields, and easily extended with additional dressing
frequencies.Comment: 16 pages, 6 figure
Probing multiple-frequency atom-photon interactions with ultracold atoms
We dress atoms with multiple-radiofrequency fields and investigate the
spectrum of transitions driven by an additional probe field. A complete
theoretical description of this rich spectrum is presented, in which we find
allowed transitions and determine their amplitudes using the resolvent
formalism. Experimentally, we observe transitions up to sixth order in the
probe field using radiofrequency spectroscopy of Bose-Einstein condensates
trapped in single- and multiple-radiofrequency-dressed potentials. We find
excellent agreement between theory and experiment, including the prediction and
verification of previously unobserved transitions, even in the
single-radiofrequency case.Comment: 20 pages, 7 figure
Applying machine learning optimization methods to the production of a quantum gas
We apply three machine learning strategies to optimize the atomic cooling
processes utilized in the production of a Bose-Einstein condensate (BEC). For
the first time, we optimize both laser cooling and evaporative cooling
mechanisms simultaneously. We present the results of an evolutionary
optimization method (Differential Evolution), a method based on non-parametric
inference (Gaussian Process regression) and a gradient-based function
approximator (Artificial Neural Network). Online optimization is performed
using no prior knowledge of the apparatus, and the learner succeeds in creating
a BEC from completely randomized initial parameters. Optimizing these cooling
processes results in a factor of four increase in BEC atom number compared to
our manually-optimized parameters. This automated approach can maintain
close-to-optimal performance in long-term operation. Furthermore, we show that
machine learning techniques can be used to identify the main sources of
instability within the apparatus.Comment: 19 pages, 7 figures, 1 tabl
Decision-making and referral processes for patients with motor neurone disease: a qualitative study of GP experiences and evaluation of a new decision-support tool
Background
The diagnosis of motor neurone disease (MND) is known to be challenging and there may be delay in patients receiving a correct diagnosis. This study investigated the referral process for patients who had been diagnosed with MND, and whether a newly-developed tool (The Red Flags checklist) might help General Practitioners (GPs) in making referral decisions.
Methods
We carried out interviews with GPs who had recently referred a patient diagnosed with MND, and interviews/surveys with GPs who had not recently referred a patient with suspected MND. We collected data before the Red Flags checklist was introduced; and again one year later. We analysed the data to identify key recurring themes.
Results
Forty two GPs took part in the study. The presence of fasciculation was the clinical feature that most commonly led to consideration of a potential MND diagnosis. GPs perceived that their role was to make onward referrals rather than attempting to make a diagnosis, and delays in correct diagnosis tended to occur at the specialist level. A quarter of participants had some awareness of the newly-developed tool; most considered it useful, if incorporated into existing systems.
Conclusions
While fasciculation is the most common symptom associated with MND, other bulbar, limb or respiratory features, together with progression should be considered. There is a need for further research into how decision-support tools should be designed and provided, in order to best assist GPs with referral decisions. There is also a need for further work at the level of secondary care, in order that referrals made are re-directed appropriately
Matter-wave Atomic Gradiometer Interferometric Sensor (MAGIS-100)
MAGIS-100 is a next-generation quantum sensor under construction at Fermilab
that aims to explore fundamental physics with atom interferometry over a
100-meter baseline. This novel detector will search for ultralight dark matter,
test quantum mechanics in new regimes, and serve as a technology pathfinder for
future gravitational wave detectors in a previously unexplored frequency band.
It combines techniques demonstrated in state-of-the-art 10-meter-scale atom
interferometers with the latest technological advances of the world's best
atomic clocks. MAGIS-100 will provide a development platform for a future
kilometer-scale detector that would be sufficiently sensitive to detect
gravitational waves from known sources. Here we present the science case for
the MAGIS concept, review the operating principles of the detector, describe
the instrument design, and study the detector systematics.Comment: 65 pages, 18 figure
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