Effect of Predeparture Testing on Postarrival SARS-CoV-2-Positive Test Results Among International Travelers - CDC Traveler-Based Genomic Surveillance Program, Four U.S. Airports, March-September 2022.

Beginning December 6, 2021, all international air passengers boarding flights to the United States were required to show either a negative result from a SARS-CoV-2 viral test taken ≤1 day before departure or proof of recovery from COVID-19 within the preceding 90 days (1). As of June 12, 2022, predeparture testing was no longer mandatory but remained recommended by CDC (2,3). Various modeling studies have estimated that predeparture testing the day before or the day of air travel reduces transmission or importation of SARS-CoV-2 by 31%-76% (4-7). Postarrival SARS-CoV-2 pooled testing data from CDC's Traveler-based Genomic Surveillance program were used to compare SARS-CoV-2 test results among volunteer travelers arriving at four U.S. airports during two 12-week periods: March 20-June 11, 2022, when predeparture testing was required, and June 12-September 3, 2022, when predeparture testing was not required. In a multivariable logistic regression model, pooled nasal swab specimens collected during March 20-June 11 were 52% less likely to be positive for SARS-CoV-2 than were those collected during June 12-September 3, after adjusting for COVID-19 incidence in the flight's country of origin, sample pool size, and collection airport (adjusted odds ratio [aOR] = 0.48, 95% CI = 0.39-0.58) (p<0.001). These findings support predeparture testing as a tool for reducing travel-associated SARS-CoV-2 transmission and provide important real-world evidence that can guide decisions for future outbreaks and pandemics.

Single-photon emission from single InGaAs/GaAs quantum dots grown by droplet epitaxy at high substrate temperature.

The authors report single-photon emission from InGaAs quantum dots grown by droplet epitaxy on (100) GaAs substrates using a solid-source molecular beam epitaxy system at elevated substrate temperatures above 400°C without post-growth annealing. High-resolution micro-photoluminescence spectroscopy exhibits sharp excitonic emissions with lifetimes ranging from 0.7 to 1.1 ns. The coherence properties of the emitted photons are investigated by measuring the first-order field correlation function.

A scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid devices.

Integrated quantum optical hybrid devices consist of fundamental constituents such as single emitters and tailored photonic nanostructures. A reliable fabrication method requires the controlled deposition of active nanoparticles on arbitrary nanostructures with highest precision. Here, we describe an easily adaptable technique that employs picking and placing of nanoparticles with an atomic force microscope combined with a confocal setup. In this way, both the topography and the optical response can be monitored simultaneously before and after the assembly. The technique can be applied to arbitrary particles. Here, we focus on nanodiamonds containing single nitrogen vacancy centers, which are particularly interesting for quantum optical experiments on the single photon and single emitter level.

Single defect centers in diamond nanocrystals as quantum probes for plasmonic nanostructures.

We present two applications of a single nitrogen vacancy center in a nanodiamond as quantum probe for plasmonic nanostructures. Coupling to the nanostructures is achieved in a highly controlled manner by picking up a pre-characterized nanocrystal with an atomic force microscope and placing it at the desired position. Local launching of single excitations into a nanowire with a spatial control of few nanometers is demonstrated. Further, a two dimensional map of the electromagnetic environment of a plasmonic bowtie antenna was derived, resembling an ultimate limit of fluorescence lifetime nanoscopy.

Fiber-integrated diamond-based single photon source.

An alignment free, micrometer-scale single photon source consisting of a single quantum emitter on an optical fiber operating at room temperature is demonstrated. It easily integrates into fiber optic networks for quantum cryptography or quantum metrology applications.(1) Near-field coupling of a single nitrogen-vacancy center is achieved in a bottom-up approach by placing a preselected nanodiamond directly on the fiber facet. Its high photon collection efficiency is equivalent to a far-field collection via an objective with a numerical aperture of 0.82. Furthermore, simultaneous excitation and re-collection through the fiber is possible by introducing a fiber-connected single emitter sensor.

Nanoassembled plasmonic-photonic hybrid cavity for tailored light-matter coupling.

We propose and demonstrate a hybrid cavity system in which metal nanoparticles are evanescently coupled to a dielectric photonic crystal cavity using a nanoassembly method. While the metal constituents lead to strongly localized fields, optical feedback is provided by the surrounding photonic crystal structure. The combined effect of plasmonic field enhancement and high quality factor (Q approximately 900) opens new routes for the control of light-matter interaction at the nanoscale.

Plasmon-enhanced upconversion in single NaYF4:Yb3+/Er3+ codoped nanocrystals.

In this Letter we report the plasmon-enhanced upconversion in single NaYF(4) nanocrystals codoped with Yb(3+)/Er(3+). Single nanocrystals and gold nanospheres are investigated and assembled in a combined confocal and atomic force microscope setup. The nanocrystals show strong upconversion emission in the green and red under excitation with a continuous wave laser in the near-infrared at 973 nm. By the use of the atomic force microscope, we couple single nanocrystals with gold spheres (30 and 60 nm in diameter) to obtain enhanced upconversion emission. An overall enhancement factor of 3.8 is reached. A comparison of time-resolved measurements on the bare nanocrystal and the coupled nanocrystal-gold sphere systems unveil that faster excitation as well as faster emission occurs in the nanocrystals.

Plasmon-enhanced single photon emission from a nanoassembled metal-diamond hybrid structure at room temperature.

In this Letter we present the controlled coupling of a single nitrogen vacancy center to a plasmonic structure. With the help of an atomic force microscope, a single nanodiamond containing a single nitrogen vacancy center and two gold nanospheres are assembled step-by-step. We show that both the excitation rate and the radiative decay rate of the color center are enhanced by about 1 order of magnitude, while the single photon character of the emission is maintained. Hot spots between diamond and gold nanoparticles provide an efficient near-field coupling, despite the mismatch in size and shape. Our approach provides hybrid systems as important building blocks for novel nanophotonic light sources in advanced plasmonic devices stable even at room temperature.

A high-temperature single-photon source from nanowire quantum dots.

We present a high-temperature single-photon source based on a quantum dot inside a nanowire. The nanowires were grown by molecular beam epitaxy in the vapor-liquid-solid growth mode. We utilize a two-step process that allows a thin, defect-free ZnSe nanowire to grow on top of a broader, cone-shaped nanowire. Quantum dots are formed by incorporating a narrow zone of CdSe into the nanowire. We observe intense and highly polarized photoluminescence even from a single emitter. Efficient photon antibunching is observed up to 220 K, while conserving a normalized antibunching dip of at most 36%. This is the highest reported temperature for single-photon emission from a nonblinking quantum-dot source and principally allows compact and cheap operation by using Peltier cooling.