Optimized Protocols for Duplex Quantum Transduction.

Quantum transducers convert quantum signals through hybrid interfaces of physical platforms in quantum networks. Modeled as quantum communication channels, performance of unidirectional quantum transduction can be measured by the quantum channel capacity. However, characterizing performance of quantum transducers used for duplex quantum transduction where signals are converted bidirectionally remains an open question. Here, we propose rate regions to characterize the performance of duplex quantum transduction. Using this tool, we find that quantum transducers optimized for simultaneous duplex transduction can outperform strategies based on the standard protocol of time-shared unidirectional transduction. Integrated over the frequency domain, we demonstrate that the rate region can also characterize quantum transducers with finite bandwidth.

Effect of Fluoride Varnish in Preventing Dental Caries of First Permanent Molars: A 24-Month Cluster Randomized Controlled Trial.

BACKGROUND: Caries is a prevalent health problem. This study evaluated the effect of fluoride varnish in preventing dental caries of first permanent molars. METHODS: The study was designed as a stratified cluster randomized controlled trial, with classes as the unit of randomization. Classes stratified by district were followed for 24 months. All eligible children of the selected classes were included for the trial. The children in the test group were biannually applied fluoride varnish. The outcomes were measured at an individual level. RESULTS: In total, 107 classes (51 in the test group, 56 in the control group) were recruited for the trial. Of the 5397 participants, 5005 children (2385 in the test group, 2620 in the control group) completed the study. At the 24-month follow-up, the mean decayed and filled surface increment of the first permanent molars of the children in the test group was significantly lower than that of the children in the control group (0.38 versus 0.61). The caries incidence of the first permanent molars in the test group was 17.0%, while that of the control group was 23.7%, with a PF of 28.3%. CONCLUSIONS: Semi-annual application of fluoride varnish is effective in reducing the caries increments of first permanent molars.

Skopi: a simulation package for diffractive imaging of noncrystalline biomolecules.

X-ray free-electron lasers (XFELs) have the ability to produce ultra-bright femtosecond X-ray pulses for coherent diffraction imaging of biomolecules. While the development of methods and algorithms for macromolecular crystallography is now mature, XFEL experiments involving aerosolized or solvated biomolecular samples offer new challenges in terms of both experimental design and data processing. Skopi is a simulation package that can generate single-hit diffraction images for reconstruction algorithms, multi-hit diffraction images of aggregated particles for training machine learning classifiers using labeled data, diffraction images of randomly distributed particles for fluctuation X-ray scattering algorithms, and diffraction images of reference and target particles for holographic reconstruction algorithms. Skopi is a resource to aid feasibility studies and advance the development of algorithms for noncrystalline experiments at XFEL facilities.

Quantum state preparation and tomography of entangled mechanical resonators.

Precisely engineered mechanical oscillators keep time, filter signals and sense motion, making them an indispensable part of the technological landscape of today. These unique capabilities motivate bringing mechanical devices into the quantum domain by interfacing them with engineered quantum circuits. Proposals to combine microwave-frequency mechanical resonators with superconducting devices suggest the possibility of powerful quantum acoustic processors1-3. Meanwhile, experiments in several mechanical systems have demonstrated quantum state control and readout4,5, phonon number resolution6,7 and phonon-mediated qubit-qubit interactions8,9. At present, these acoustic platforms lack processors capable of controlling the quantum states of several mechanical oscillators with a single qubit and the rapid quantum non-demolition measurements of mechanical states needed for error correction. Here we use a superconducting qubit to control and read out the quantum state of a pair of nanomechanical resonators. Our device is capable of fast qubit-mechanics swap operations, which we use to deterministically manipulate the mechanical states. By placing the qubit into the strong dispersive regime with both mechanical resonators simultaneously, we determine the phonon number distributions of the resonators by means of Ramsey measurements. Finally, we present quantum tomography of the prepared nonclassical and entangled mechanical states. Our result represents a concrete step towards feedback-based operation of a quantum acoustic processor.

Room-Temperature Mechanical Resonator with a Single Added or Subtracted Phonon.

A room-temperature mechanical oscillator undergoes thermal Brownian motion with an amplitude much larger than the amplitude associated with a single phonon of excitation. This motion can be read out and manipulated using laser light using a cavity-optomechanical approach. By performing a strong quantum measurement (i.e., counting single photons in the sidebands imparted on a laser), we herald the addition and subtraction of single phonons on the 300 K thermal motional state of a 4 GHz mechanical oscillator. To understand the resulting mechanical state, we implement a tomography scheme and observe highly non-Gaussian phase-space distributions. Using a maximum likelihood method, we infer the density matrix of the oscillator, and we confirm the counterintuitive doubling of the mean phonon number resulting from phonon addition and subtraction.

Effect of Fluoride Varnish in Caries Prevention on Permanent First Molars: A 36-Month Cluster Randomized Controlled Trial.

Purpose: The purpose of this study was to evaluate the effect of fluoride varnish in preventing dental caries of permanent first molars (PFMs). Methods: The study was designed to be a stratified-cluster randomized controlled trial with classes used as the unit of randomization. Classes stratified by district were followed for 36 months. All eligible children of the selected classes were included in the trial. The children in the test group were applied fluoride varnish biannually. The outcomes were measured at the individual level. Results: In total, 107 classes (51 in the test group, 56 in the control group) were recruited for the trial. Among the 5,397 total subjects, 5,005 and 4,596 children completed the 24-month and 36-month course, respectively. There were no group differences at baseline (P>0.05). The mean decayed and filled surfaces scores of the test group were significantly lower than those of the control group at the 36-month follow-up (P<0.05). The caries processing speed of PFMs increased from 24 months to 36 months; however, group differences were not significant (ß equals 0.01; P>0.05). Conclusions: Biannual application of fluoride varnish can effectively prevent dental caries of six- to seven-year-old children. Nevertheless, the use of fluoride varnish with additional treatments (such as pit and fissure sealants) should be considered for optimized benefit after 24 months.

Resolving the energy levels of a nanomechanical oscillator.

The quantum nature of an oscillating mechanical object is anything but apparent. The coherent states that describe the classical motion of a mechanical oscillator do not have a well defined energy, but are quantum superpositions of equally spaced energy eigenstates. Revealing this quantized structure is only possible with an apparatus that measures energy with a precision greater than the energy of a single phonon. One way to achieve this sensitivity is by engineering a strong but nonresonant interaction between the oscillator and an atom. In a system with sufficient quantum coherence, this interaction allows one to distinguish different energy eigenstates using resolvable differences in the atom's transition frequency. For photons, such dispersive measurements have been performed in cavity1,2 and circuit quantum electrodynamics3. Here we report an experiment in which an artificial atom senses the motional energy of a driven nanomechanical oscillator with sufficient sensitivity to resolve the quantization of its energy. To realize this, we build a hybrid platform that integrates nanomechanical piezoelectric resonators with a microwave superconducting qubit on the same chip. We excite phonons with resonant pulses and probe the resulting excitation spectrum of the qubit to observe phonon-number-dependent frequency shifts that are about five times larger than the qubit linewidth. Our result demonstrates a fully integrated platform for quantum acoustics that combines large couplings, considerable coherence times and excellent control over the mechanical mode structure. With modest experimental improvements, we expect that our approach will enable quantum nondemolition measurements of phonons4 and will lead to quantum sensors and information-processing approaches5 that use chip-scale nanomechanical devices.

Prevalence and contributing factors of dental caries of 6-year-old children in four regions of China.

BACKGROUND: From 2005 to 2015, the prevalence of dental caries in both primary and permanent dentitions was significantly increased in China. Previous studies have shown that the prevalence of permanent dental caries in school-aged children had already reached 19.7%-54.0%, 97.5% affecting first permanent molars. This study aimed to investigate the prevalence and contributing factors of dental caries in 6-year-old children in four regions of China to provide information for oral health promotion programs. METHODS: A randomized cluster sampling method was employed in the study. All 6-year-old first grade children from the selected schools were invited to receive a clinical oral examination. Dental caries were diagnosed according to the World Health Organization criteria. The erupting first permanent molars were recorded using the modified International Caries Detection Assessment System. Questionnaires assessing children's oral health-related behaviors and their caretakers' oral health awareness and attitudes were completed by the children's parents or guardians. RESULTS: Overall, 4,936 6-year-old school children participated in the survey. The prevalence of caries among these children was 87.7%, with a mean number of decayed, missing and filled teeth of 6.04 (SD, 4.24). In primary dentition, the caries prevalence was 87.7%, and the mean dmft score was 6.01 (SD, 4.22). In permanent dentition, the caries prevalence was 2.0%, the mean DFS score was 0.04 (SD, 0.31). All permanent dental caries occurred on the first permanent molars. Carious tooth surfaces were identified as modified ICDAS code "A" to indicate initial caries and distinct visual change in enamel. The mean DAS score of non-cavitated caries in the first permanent molars was 0.18 (SD, 0.67). Logistic regression analysis showed that regional and gender factors were significantly related to the caries experience of these children. CONCLUSIONS: The 6-year-old children from four regions of China had sever primary dental caries and the first permanent molars were at high risk for dental caries. It is critical to protect permanent teeth from caries as early as the eruption of the first permanent molars.

Painting Nonclassical States of Spin or Motion with Shaped Single Photons.

We propose a robust scheme for generating macroscopic superposition states of spin or motion with the aid of a single photon. Shaping the wave packet of the photon enables high-fidelity preparation of nonclassical states of matter even in the presence of photon loss. Success is heralded by photodetection, enabling the scheme to be implemented with a weak coherent field. We analyze applications to preparing Schrödinger cat states of a collective atomic spin or of a mechanical oscillator coupled to an optical resonator. The method generalizes to preparing arbitrary superpositions of coherent states, enabling full quantum control. We illustrate this versatility by showing how to prepare Dicke or Fock states, as well as superpositions in the Dicke or Fock basis.

Single-Mode Phononic Wire.

Photons and electrons transmit information to form complex systems and networks. Phonons on the other hand, the quanta of mechanical motion, are often considered only as carriers of thermal energy. Nonetheless, their flow can also be molded in fabricated nanoscale circuits. We design and experimentally demonstrate wires for phonons by patterning the surface of a silicon chip. Our device eliminates all but one channel of phonon conduction, allowing coherent phonon transport over millimeter length scales. We characterize the phononic wire optically, by coupling it strongly to an optomechanical transducer. The phononic wire enables new ways to manipulate information and energy on a chip. In particular, our result is an important step towards realizing on-chip phonon networks, in which quantum information is transmitted between nodes via phonons.

Enhancing a slow and weak optomechanical nonlinearity with delayed quantum feedback.

A central goal of quantum optics is to generate large interactions between single photons so that one photon can strongly modify the state of another one. In cavity optomechanics, photons interact with the motional degrees of freedom of an optical resonator, for example, by imparting radiation pressure forces on a movable mirror or sensing minute fluctuations in the position of the mirror. Here, we show that the optical nonlinearity arising from these effects, typically too small to operate on single photons, can be sufficiently enhanced with feedback to generate large interactions between single photons. We propose a protocol that allows photons propagating in a waveguide to interact with each other through multiple bounces off an optomechanical system. The protocol is analysed by evolving the full many-body quantum state of the waveguide-coupled system, illustrating that large photon-photon interactions mediated by mechanical motion may be within experimental reach.