350 research outputs found
Lasing on a narrow transition in a cold thermal strontium ensemble
Highly stable laser sources based on narrow atomic transitions provide a
promising platform for direct generation of stable and accurate optical
frequencies. Here we investigate a simple system operating in the
high-temperature regime of cold atoms. The interaction between a thermal
ensemble of Sr at mK temperatures and a medium-finesse cavity produces
strong collective coupling and facilitates high atomic coherence which causes
lasing on the dipole forbidden SP transition. We
experimentally and theoretically characterize the lasing threshold and
evolution of such a system, and investigate decoherence effects in an
unconfined ensemble. We model the system using a Tavis-Cummings model, and
characterize velocity-dependent dynamics of the atoms as well as the dependency
on the cavity-detuning.Comment: 9 pages, 7 figure
Observation of Motion Dependent Nonlinear Dispersion with Narrow Linewidth Atoms in an Optical Cavity
As an alternative to state-of-the-art laser frequency stabilisation using
ultra-stable cavities, it has been proposed to exploit the non-linear effects
from coupling of atoms with a narrow transition to an optical cavity. Here we
have constructed such a system and observed non-linear phase shifts of a narrow
optical line by strong coupling of a sample of strontium-88 atoms to an optical
cavity. The sample temperature of a few mK provides a domain where the Doppler
energy scale is several orders of magnitude larger than the narrow linewidth of
the optical transition. This makes the system sensitive to velocity dependent
multi-photon scattering events (Dopplerons) that affect the cavity field
transmission and phase. By varying the number of atoms and the intra-cavity
power we systematically study this non-linear phase signature which displays
roughly the same features as for much lower temperature samples. This
demonstration in a relatively simple system opens new possibilities for
alternative routes to laser stabilization at the sub 100 mHz level and
superradiant laser sources involving narrow line atoms. The understanding of
relevant motional effects obtained here has direct implications for other
atomic clocks when used in relation with ultranarrow clock transitions.Comment: 9 pages (including 4 pages of Supplemental Information), 6 figures.
Updated to correspond to the published versio
Non-linear Spectroscopy of Sr Atoms in an Optical Cavity for Laser Stabilization
We study the non-linear interaction of a cold sample of strontium-88 atoms
coupled to a single mode of a low finesse optical cavity in the so-called bad
cavity limit and investigate the implications for applications to laser
stabilization. The atoms are probed on the weak inter-combination line \lvert
5s^{2} \, ^1 \textrm{S}_0 \rangle \,-\, \lvert 5s5p \, ^3 \textrm{P}_1 \rangle
at 689 nm in a strongly saturated regime. Our measured observables include the
atomic induced phase shift and absorption of the light field transmitted
through the cavity represented by the complex cavity transmission coefficient.
We demonstrate high signal-to-noise-ratio measurements of both quadratures -
the cavity transmitted phase and absorption - by employing FM spectroscopy
(NICE-OHMS). We also show that when FM spectroscopy is employed in connection
with a cavity locked to the probe light, observables are substantially modified
compared to the free space situation where no cavity is present. Furthermore,
the non-linear dynamics of the phase dispersion slope is experimentally
investigated and the optimal conditions for laser stabilization are
established. Our experimental results are compared to state-of-the-art cavity
QED theoretical calculations.Comment: 7 pages, 4 figure
Isotope shifts of the (3s3p)P - (3s4s)S Mg I transitions
We report measurements of the isotope shifts of the (3s3p)P -
(3s4s)S Mg I transitions for the stable isotopes Mg (I=0),
Mg (I=5/2) and Mg (I=0). Furthermore the Mg S
hyperfine coefficient A(S) = (-321.6 1.5) MHz is extracted and
found to be in excellent agreement with state-of-the-art theoretical
predictions giving A(S) = -325 MHz and B(S)
MHz. Compared to previous measurements, the data presented in this work is
improved up to a factor of ten.Comment: 4 pages, 4 figures submitted to PR
Collectively enhanced Ramsey readout by cavity sub- to superradiant transition
When an inverted ensemble of atoms is tightly packed on the scale of its
emission wavelength or when the atoms are collectively strongly coupled to a
single cavity mode, their dipoles will align and decay rapidly via a
superradiant burst. However, a spread-out dipole phase distribution theory
predicts a required minimum threshold of atomic excitation for superradiance to
occur. Here we experimentally confirm this predicted threshold for superradiant
emission on a narrow optical transition when exciting the atoms transversely
and show how to take advantage of the resulting sub- to superradiant
transition. A -pulse places the atoms in a subradiant state, protected
from collective cavity decay, which we exploit during the free evolution period
in a corresponding Ramsey pulse sequence. The final excited state population is
read out via superradiant emission from the inverted atomic ensemble after a
second -pulse, and with minimal heating this allows for multiple Ramsey
sequences within one experimental cycle. Our scheme is a fundamentally new
approach to atomic state readout characterized by its speed, simplicity, and
high sensitivity. It demonstrates the potential of sensors using collective
effects in cavity-coupled quantum emitters
SARS-CoV-2 vaccination and myocarditis or myopericarditis:population based cohort study
OBJECTIVE: To investigate the association between SARS-CoV-2 vaccination and myocarditis or myopericarditis. DESIGN: Population based cohort study. SETTING: Denmark. PARTICIPANTS: 4â931â775 individuals aged 12 years or older, followed from 1 October 2020 to 5 October 2021. MAIN OUTCOME MEASURES: The primary outcome, myocarditis or myopericarditis, was defined as a combination of a hospital diagnosis of myocarditis or pericarditis, increased troponin levels, and a hospital stay lasting more than 24 hours. Follow-up time before vaccination was compared with follow-up time 0-28 days from the day of vaccination for both first and second doses, using Cox proportional hazards regression with age as an underlying timescale to estimate hazard ratios adjusted for sex, comorbidities, and other potential confounders. RESULTS: During follow-up, 269 participants developed myocarditis or myopericarditis, of whom 108 (40%) were 12-39 years old and 196 (73%) were male. Of 3â482â295 individuals vaccinated with BNT162b2 (Pfizer-BioNTech), 48 developed myocarditis or myopericarditis within 28 days from the vaccination date compared with unvaccinated individuals (adjusted hazard ratio 1.34 (95% confidence interval 0.90 to 2.00); absolute rate 1.4 per 100â000 vaccinated individuals within 28 days of vaccination (95% confidence interval 1.0 to 1.8)). Adjusted hazard ratios among female participants only and male participants only were 3.73 (1.82 to 7.65) and 0.82 (0.50 to 1.34), respectively, with corresponding absolute rates of 1.3 (0.8 to 1.9) and 1.5 (1.0 to 2.2) per 100â000 vaccinated individuals within 28 days of vaccination, respectively. The adjusted hazard ratio among 12-39 year olds was 1.48 (0.74 to 2.98) and the absolute rate was 1.6 (1.0 to 2.6) per 100â000 vaccinated individuals within 28 days of vaccination. Among 498â814 individuals vaccinated with mRNA-1273 (Moderna), 21 developed myocarditis or myopericarditis within 28 days from vaccination date (adjusted hazard ratio 3.92 (2.30 to 6.68); absolute rate 4.2 per 100â000 vaccinated individuals within 28 days of vaccination (2.6 to 6.4)). Adjusted hazard ratios among women only and men only were 6.33 (2.11 to 18.96) and 3.22 (1.75 to 5.93), respectively, with corresponding absolute rates of 2.0 (0.7 to 4.8) and 6.3 (3.6 to 10.2) per 100â000 vaccinated individuals within 28 days of vaccination, respectively. The adjusted hazard ratio among 12-39 year olds was 5.24 (2.47 to 11.12) and the absolute rate was 5.7 (3.3 to 9.3) per 100â000 vaccinated individuals within 28 days of vaccination. CONCLUSIONS: Vaccination with mRNA-1273 was associated with a significantly increased risk of myocarditis or myopericarditis in the Danish population, primarily driven by an increased risk among individuals aged 12-39 years, while BNT162b2 vaccination was only associated with a significantly increased risk among women. However, the absolute rate of myocarditis or myopericarditis after SARS-CoV-2 mRNA vaccination was low, even in younger age groups. The benefits of SARS-CoV-2 mRNA vaccination should be taken into account when interpreting these findings. Larger multinational studies are needed to further investigate the risks of myocarditis or myopericarditis after vaccination within smaller subgroups
Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru
The intraseasonal evolution of physical and biogeochemical properties during a coastal trapped wave event off central Peru is analysed using data from an extensive shipboard observational programme conducted between April and June 2017, and remote sensing data. The poleward velocities in the PeruâChile Undercurrent were highly variable and strongly intensified to above 0.5âmâsâ1 between the middle and end of May. This intensification was likely caused by a first-baroclinic-mode downwelling coastal trapped wave, excited by a westerly wind anomaly at the Equator and originating at about 95ââW. Local winds along the South American coast did not impact the wave. Although there is general agreement between the observed cross-shore-depth velocity structure of the coastal trapped wave and the velocity structure of first vertical mode solution of a linear wave model, there are differences in the details of the two flow distributions. The enhanced poleward flow increased water mass advection from the equatorial current system to the study site. The resulting shorter alongshore transit times between the Equator and the coast off central Peru led to a strong increase in nitrate concentrations, less anoxic water, likely less fixed nitrogen loss to N2 and a decrease of the nitrogen deficit compared to the situation before the poleward flow intensification. This study highlights the role of changes in the alongshore advection due to coastal trapped waves for the nutrient budget and the cumulative strength of N cycling in the Peruvian oxygen minimum zone. Enhanced availability of nitrate may impact a range of pelagic and benthic elemental cycles, as it represents a major electron acceptor for organic carbon degradation during denitrification and is involved in sulfide oxidation in sediments
Circulating Lipoproteins Are a Crucial Component of Host Defense against Invasive Salmonella typhimurium Infection
Contains fulltext :
79883.pdf (Publisherâs version ) (Open Access)BACKGROUND: Circulating lipoproteins improve the outcome of severe Gram-negative infections through neutralizing lipopolysaccharides (LPS), thus inhibiting the release of proinflammatory cytokines. METHODS/PRINCIPAL FINDINGS: Low density lipoprotein receptor deficient (LDLR-/-) mice, with a 7-fold increase in LDL, are resistant against infection with Salmonella typhimurium (survival 100% vs 5%, p<0.001), and 100 to 1000-fold lower bacterial burden in the organs, compared with LDLR+/+ mice. Protection was not due to differences in cytokine production, phagocytosis, and killing of Salmonella organisms. The differences were caused by the excess of lipoproteins, as hyperlipoproteinemic ApoE-/- mice were also highly resistant to Salmonella infection. Lipoproteins protect against infection by interfering with the binding of Salmonella to host cells, and preventing organ invasion. This leads to an altered biodistribution of the microorganisms during the first hours of infection: after intravenous injection of Salmonella into LDLR+/+ mice, the bacteria invaded the liver and spleen within 30 minutes of infection. In contrast, in LDLR-/- mice, Salmonella remained constrained to the circulation from where they were efficiently cleared, with decreased organ invasion. CONCLUSIONS: plasma lipoproteins are a potent host defense mechanism against invasive Salmonella infection, by blocking adhesion of Salmonella to the host cells and subsequent tissue invasion
Guidelines for developing optical clocks with fractional frequency uncertainty
There has been tremendous progress in the performance of optical frequency
standards since the first proposals to carry out precision spectroscopy on
trapped, single ions in the 1970s. The estimated fractional frequency
uncertainty of today's leading optical standards is currently in the
range, approximately two orders of magnitude better than that of the best
caesium primary frequency standards. This exceptional accuracy and stability is
resulting in a growing number of research groups developing optical clocks.
While good review papers covering the topic already exist, more practical
guidelines are needed as a complement. The purpose of this document is
therefore to provide technical guidance for researchers starting in the field
of optical clocks. The target audience includes national metrology institutes
(NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD
students and postdocs entering the field. Another potential audience is
academic groups with experience in atomic physics and atom or ion trapping, but
with less experience of time and frequency metrology and optical clock
requirements. These guidelines have arisen from the scope of the EMPIR project
"Optical clocks with uncertainty" (OC18). Therefore, the
examples are from European laboratories even though similar work is carried out
all over the world. The goal of OC18 was to push the development of optical
clocks by improving each of the necessary subsystems: ultrastable lasers,
neutral-atom and single-ion traps, and interrogation techniques. This document
shares the knowledge acquired by the OC18 project consortium and gives
practical guidance on each of these aspects
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