421 research outputs found
Approaching the adiabatic timescale with machine-learning
The control and manipulation of quantum systems without excitation is
challenging, due to the complexities in fully modeling such systems accurately
and the difficulties in controlling these inherently fragile systems
experimentally. For example, while protocols to decompress Bose-Einstein
condensates (BEC) faster than the adiabatic timescale (without excitation or
loss) have been well developed theoretically, experimental implementations of
these protocols have yet to reach speeds faster than the adiabatic timescale.
In this work, we experimentally demonstrate an alternative approach based on a
machine learning algorithm which makes progress towards this goal. The
algorithm is given control of the coupled decompression and transport of a
metastable helium condensate, with its performance determined after each
experimental iteration by measuring the excitations of the resultant BEC. After
each iteration the algorithm adjusts its internal model of the system to create
an improved control output for the next iteration. Given sufficient control
over the decompression, the algorithm converges to a novel solution that sets
the current speed record in relation to the adiabatic timescale, beating out
other experimental realizations based on theoretical approaches. This method
presents a feasible approach for implementing fast state preparations or
transformations in other quantum systems, without requiring a solution to a
theoretical model of the system. Implications for fundamental physics and
cooling are discussed.Comment: 7 pages main text, 2 pages supporting informatio
Production of a highly degenerate Fermi gas of metastable helium-3 atoms
We report on the achievement of quantum degeneracy in both components of a
Bose-Fermi mixture of metastable helium atoms, He* and He*. Degeneracy
is achieved via Doppler cooling and forced evaporation for He*, and
sympathetically cooling He* with He*. We discuss our simplified
implementation, along with the high versatility of our system. This technique
is able to produce a degenerate Fermi gas with a minimum reduced temperature of
, consisting of He* atoms. Due to the high
internal energy of both isotopes single atom detection is possible, opening the
possibility of a large number of experiments into Bose-Fermi mixtures.Comment: 13 pages, 8 figure
Biannual versus annual mass azithromycin distribution and malaria seroepidemiology among preschool children in Niger: a sub-study of a cluster randomized trial.
BACKGROUND: Biannual mass azithromycin administration to preschool children reduces all-cause mortality, but the mechanism for the effect is not understood. Azithromycin has activity against malaria parasites, and malaria is a leading cause of child mortality in the Sahel. The effect of biannual versus annual azithromycin distribution for trachoma control on serological response to merozoite surface protein 1 (MSP-119), a surrogate for malaria incidence, was evaluated among children in Niger. METHODS: Markers of malaria exposure were measured in two arms of a factorial randomized controlled trial designed to evaluate targeted biannual azithromycin distribution to children under 12Â years of age compared to annual azithromycin to the entire community for trachoma control (Nâ=â12 communities per arm). Communities were treated for 36Â months (6 versus 3 distributions). Dried blood spots were collected at 36Â months among children ages 1-5Â years, and MSP-119 antibody levels were assessed using a bead-based multiplex assay to measure malaria seroprevalence. RESULTS: Antibody results were available for 991 children. MSP-119 seropositivity was 62.7% in the biannual distribution arm compared to 68.7% in the annual arm (prevalence ratio 0.91, 95% CI 0.83 to 1.00). Mean semi-quantitative antibody levels were lower in the biannual distribution arm compared to the annual arm (mean difference -â0.39, 95% CI -â0.05 to -â0.72). CONCLUSIONS: Targeted biannual azithromycin distribution was associated with lower malaria seroprevalence compared to that in a population that received annual distribution. Trial Registration Clinicaltrials.gov NCT00792922
Voltage scanning and technical upgrades at the Collinear Resonance Ionization Spectroscopy experiment
To optimize the performance of the Collinear Resonance Ionization
Spectroscopy (CRIS) experiment at CERN-ISOLDE, technical upgrades are
continuously introduced, aiming to enhance its sensitivity, precision,
stability, and efficiency. Recently, a voltage-scanning setup was developed and
commissioned at CRIS, which improved the scanning speed by a factor of three as
compared to the current laser-frequency scanning approach. This leads to faster
measurements of the hyperfine structure for systems with high yields (more than
a few thousand ions per second). Additionally, several beamline sections have
been redesigned and manufactured, including a new field-ionization unit, a
sharper electrostatic bend, and improved ion optics. The beamline upgrades are
expected to yield an improvement of at least a factor of 5 in the
signal-to-noise ratio by suppressing the non-resonant laser ions and providing
time-of-flight separation between the resonant ions and the collisional
background. Overall, the presented developments will further improve the
selectivity, sensitivity, and efficiency of the CRIS technique.Comment: 10 pages. Under review at NIM B as part of the proceedings of EMIS
2022 at RAON, South Kore
Radio source calibration for the VSA and other CMB instruments at around 30 GHz
Accurate calibration of data is essential for the current generation of CMB
experiments. Using data from the Very Small Array (VSA), we describe procedures
which will lead to an accuracy of 1 percent or better for experiments such as
the VSA and CBI. Particular attention is paid to the stability of the receiver
systems, the quality of the site and frequent observations of reference
sources. At 30 GHz the careful correction for atmospheric emission and
absorption is shown to be essential for achieving 1 percent precision. The
sources for which a 1 percent relative flux density calibration was achieved
included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and
Saturn. A flux density, or brightness temperature in the case of the planets,
was derived at 33 GHz relative to Jupiter which was adopted as the fundamental
calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027
and Venus were examined for variability. Cas A was found to be decreasing at
percent per year over the period March 2001 to August 2004.
In the same period Tau A was decreasing at percent per year. A
survey of the published data showed that the planetary nebula NGC7027 decreased
at percent per year over the period 1967 to 2003. Venus showed
an insignificant ( percent) variation with Venusian illumination.
The integrated polarization of Tau A at 33 GHz was found to be
percent at pa .}Comment: 13 pages, 15 figures, submitted to MNRA
Zn loading effects on the selectivity of PdZn catalysts for CO2 hydrogenation to methanol
PdZn/TiO2 catalysts have been investigated for the hydrogenation of CO2 to methanol. Varying the ratio of Pd and Zn using TiO2 as a support has a dramatic effect on catalytic performance. Chemical vapour impregnation was used to produce PdZn alloys on TiO2 and X-ray diffraction, X-ray photoelectron spectroscopy, and scanning transmission electron microscopy revealed changes in the structure at varying total PdZn molar ratios. Compared to monometallic Pd/TiO2, introducing a low loading of Zn drastically changes product selectivity. When Pd is alloyed with Zn above a total Zn/Pdâ=â1 molar ratio, methanol selectivity is improved. Therefore, for enhanced methanol productivity, it is crucial for the Zn loading to be higher than that required for the stoichiometric formation of the 1:1 ÎČ-PdZn alloy
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