Spin Squeezing by Rydberg Dressing in an Array of Atomic Ensembles.

We report on the creation of an array of spin-squeezed ensembles of cesium atoms via Rydberg dressing, a technique that offers optical control over local interactions between neutral atoms. We optimize the coherence of the interactions by a stroboscopic dressing sequence that suppresses super-Poissonian loss. We thereby prepare squeezed states of N=200 atoms with a metrological squeezing parameter ξ^{2}=0.77(9) quantifying the reduction in phase variance below the standard quantum limit. We realize metrological gain across three spatially separated ensembles in parallel, with the strength of squeezing controlled by the local intensity of the dressing light. Our method can be applied to enhance the precision of tests of fundamental physics based on arrays of atomic clocks and to enable quantum-enhanced imaging of electromagnetic fields.

Contamination of multiuse eyedrop bottles by exhaled air from patients wearing face masks during the COVID-19 pandemic: Schlieren imaging analysis.

PURPOSE: To determine whether mask-induced redirected exhaled air through the superior mask gap contacts multiuse eyedrop bottles during drop administration and the efficacy of interventions to reduce such exposure. SETTING: Academic ophthalmology center. DESIGN: Interventional analysis. METHODS: Schlieren airflow imaging was taken of an examinee wearing frequently used face masks and enacting common clinical scenarios-with and without manual occlusion of the superior mask gap and/or neck extension-and maximum visible vertical breath plume height was quantified. Bottle height during eyedrop administration was measured for 4 ophthalmologists during instillation to 8 eyes of 4 subjects. RESULTS: Breath plume height (mean ± SD 275.5 ± 16.3 mm) was significantly greater than mean bottle height (13.9 ± 4.7 mm; P < .01). Plume height was reduced with manual mask occlusion vs without (P < .01) and was also lower than mean bottle height with manual mask occlusion (P < .01) but not in the absence of occlusion (P < .01). Neck extension alone did not adequately redirect liberated breath to prevent contact with a bottle. CONCLUSIONS: Exhaled air liberated from commonly worn patient face masks was able to contact multiuse eyedrop bottles during eyedrop administration. These findings have important patient safety implications during the coronavirus disease 2019 pandemic and with other respiratory pathogens because these multiuse bottles could potentially serve as vectors of disease. Occlusion of the superior mask gap significantly reduces breath contamination and should be strongly considered by eyecare providers during drop administration in eye clinics.

On the feasibility of life-saving locomotive bumpers.

Motivated by the thousands of pedestrians killed each year in train impacts, this paper investigates the life-saving capability of four high-level locomotive bumper concepts. The head motions produced by the four concepts are modeled as one or two square acceleration pulses and are analyzed using the Head Injury Criterion (HIC). Surprisingly, the analyses show that all four concepts can achieve HIC values of less than 200 for an impact with a locomotive traveling at 100 km/h. Two of the concepts eject the pedestrian trackside with at a velocity of roughly 40 km/h and the risk of ground-impact injury is discussed in the context of related automobile accident data. The computed bumper lengths are a fraction of the overall length of a locomotive and are thus feasible for practical implementation. One concept involves an oblique impact and the potential for rotational head injury is analyzed. This basic feasibility research motivates future investigations into the detailed design of bumper shapes, multi-body pedestrian simulations, and finite-element injury models.