190 research outputs found
Shooting for Equity: Division II Basketball Coaches\u27 Perspectives of Gender Discrimination
Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs
We advance all optical spin noise spectroscopy (SNS) in semiconductors to
detection bandwidths of several hundred gigahertz by employing an ingenious
scheme of pulse trains from ultrafast laser oscillators as an optical probe.
The ultrafast SNS technique avoids the need for optical pumping and enables
nearly perturbation free measurements of extremely short spin dephasing times.
We employ the technique to highly n-doped bulk GaAs where magnetic field
dependent measurements show unexpected large g-factor fluctuations.
Calculations suggest that such large g-factor fluctuations do not necessarily
result from extrinsic sample variations but are intrinsically present in every
doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure
Mid-infrared spectroscopy with a broadly tunable thin-film lithium niobate optical parametric oscillator
Mid-infrared spectroscopy, an important and widespread technique for sensing
molecules, has encountered barriers stemming from sources either limited in
tuning range or excessively bulky for practical field use. We present a
compact, efficient, and broadly tunable optical parametric oscillator (OPO)
device surmounting these challenges. Leveraging a dispersion-engineered
singly-resonant OPO implemented in thin-film lithium niobate-on-sapphire, we
achieve broad and controlled tuning over an octave, from 1.5 to 3.3 microns by
combining laser and temperature tuning. The device generates > 25 mW of
mid-infrared light at 3.2 microns, offering a power conversion efficiency of
15% (45% quantum efficiency). We demonstrate the tuning and performance of the
device by successfully measuring the spectra of methane and ammonia, verifying
our approach's relevance for gas sensing. Our device signifies an important
advance in nonlinear photonics miniaturization and brings practical field
applications of high-speed and broadband mid-infrared spectroscopy closer to
reality.Comment: 19 pages, 11 figure
Integrated Quantum Optical Phase Sensor
The quantum noise of light fundamentally limits optical phase sensors. A
semiclassical picture attributes this noise to the random arrival time of
photons from a coherent light source such as a laser. An engineered source of
squeezed states suppresses this noise and allows sensitivity beyond the
standard quantum limit (SQL) for phase detection. Advanced gravitational wave
detectors like LIGO have already incorporated such sources, and nascent efforts
in realizing quantum biological measurements have provided glimpses into new
capabilities emerging in quantum measurement. We need ways to engineer and use
quantum light within deployable quantum sensors that operate outside the
confines of a lab environment. Here we present a photonic integrated circuit
fabricated in thin-film lithium niobate that provides a path to meet these
requirements. We use the second-order nonlinearity to produce a squeezed state
at the same frequency as the pump light and realize circuit control and sensing
with electro-optics. Using a 26.2 milliwatts of optical power, we measure (2.7
0.2 ) squeezing and apply it to increase the signal-to-noise ratio of
phase measurement. We anticipate that on-chip photonic systems like this, which
operate with low power and integrate all of the needed functionality on a
single die, will open new opportunities for quantum optical sensing.Comment: 14 pages, 3+3 figure
Integrated frequency-modulated optical parametric oscillator
Optical frequency combs have revolutionized precision measurement,
time-keeping, and molecular spectroscopy. A substantial effort has developed
around "microcombs": integrating comb-generating technologies into compact,
reliable photonic platforms. Current approaches for generating these microcombs
involve either the electro-optic (EO) or Kerr mechanisms. Despite rapid
progress, maintaining high efficiency and wide bandwidth remains challenging.
Here, we introduce a new class of microcomb -- an integrated optical frequency
comb generator that combines electro-optics and parametric amplification to
yield a frequency-modulated optical parametric oscillator (FM-OPO). In stark
contrast to EO and Kerr combs, the FM-OPO microcomb does not form pulses but
maintains operational simplicity and highly efficient pump power utilization
with an output resembling a frequency-modulated laser. We outline the working
principles of FM-OPO and demonstrate them by fabricating the complete optical
system in thin-film lithium niobate (LNOI). We measure pump to comb internal
conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top
spectral distribution spanning approximately 1,000 modes (approximately 6 THz).
Compared to an EO comb, the cavity dispersion rather than loss determines the
FM-OPO bandwidth, enabling broadband combs with a smaller RF modulation power.
The FM-OPO microcomb, with its robust operational dynamics, high efficiency,
and large bandwidth, contributes a new approach to the field of microcombs and
promises to herald an era of miniaturized precision measurement, and
spectroscopy tools to accelerate advancements in metrology, spectroscopy,
telecommunications, sensing, and computing.Comment: 8 pages, 4 figures main text; another 19 pages and 9 figures in
methods and supplementar
Single-Mode Squeezed Light Generation and Tomography with an Integrated Optical Parametric Oscillator
Quantum optical technologies promise advances in sensing, computing, and
communication. A key resource is squeezed light, where quantum noise is
redistributed between optical quadratures. We introduce a monolithic,
chip-scale platform that exploits the nonlinearity of a thin-film
lithium niobate (TFLN) resonator device to efficiently generate squeezed states
of light. Our system integrates all essential components -- except for the
laser and two detectors -- on a single chip with an area of one square
centimeter, significantly reducing the size, operational complexity, and power
consumption associated with conventional setups. Our work addresses challenges
that have limited previous integrated nonlinear photonic implementations that
rely on either nonlinear resonators or on integrated waveguide
parametric amplifiers. Using the balanced homodyne measurement
subsystem that we implemented on the same chip, we measure a squeezing of 0.55
dB and an anti-squeezing of 1.55 dB. We use 20 mW of input power to generate
the parametric oscillator pump field by employing second harmonic generation on
the same chip. Our work represents a substantial step toward compact and
efficient quantum optical systems posed to leverage the rapid advances in
integrated nonlinear and quantum photonics.Comment: 21 pages; 4 figures in main body, 8 supplementary figure
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Advances in optical materials for large aperture lasers
Lawrence Livermore National Laboratory (LLNL) is using large aperture Nd: glass lasers to investigate the feasibility of inertial confinement fusion. In our experiments high power laser light is focussed onto a small (100 to 500 micron) target containing a deuterium-tritium fuel mixture. During the short (1 to 5 ns) laser pulse the fuel is compressed and heated, resulting in fusion reactions. The generation and control of the powerful laser pulses for these experiments is a challenging scientific and engineering task, which requires the development of new optical materials, fabrication techniques, and coatings. LLNL with the considerable cooperation and support from the optical industry, where most of the research and development and almost all the manufacturing is done, has successfully applied several new developments in these areas
Efficient Photonic Integration of Diamond Color Centers and Thin-Film Lithium Niobate
On-chip photonic quantum circuits with integrated quantum memories have the
potential to radically progress hardware for quantum information processing. In
particular, negatively charged group-IV color centers in diamond are promising
candidates for quantum memories, as they combine long storage times with
excellent optical emission properties and an optically-addressable spin state.
However, as a material, diamond lacks many functionalities needed to realize
scalable quantum systems. Thin-film lithium niobate (TFLN), in contrast, offers
a number of useful photonic nonlinearities, including the electro-optic effect,
piezoelectricity, and capabilities for periodically-poled quasi-phase matching.
Here, we present highly efficient heterogeneous integration of diamond
nanobeams containing negatively charged silicon-vacancy (SiV) centers with TFLN
waveguides. We observe greater than 90\% transmission efficiency between the
diamond nanobeam and TFLN waveguide on average across multiple measurements. By
comparing saturation signal levels between confocal and integrated collection,
we determine a -fold increase in photon counts channeled into TFLN
waveguides versus that into out-of-plane collection channels. Our results
constitute a key step for creating scalable integrated quantum photonic
circuits that leverage the advantages of both diamond and TFLN materials
Estimates of array and pool-construction variance for planning efficient DNA-pooling genome wide association studies
<p>Abstract</p> <p>Background</p> <p>Until recently, genome-wide association studies (GWAS) have been restricted to research groups with the budget necessary to genotype hundreds, if not thousands, of samples. Replacing individual genotyping with genotyping of DNA pools in Phase I of a GWAS has proven successful, and dramatically altered the financial feasibility of this approach. When conducting a pool-based GWAS, how well SNP allele frequency is estimated from a DNA pool will influence a study's power to detect associations. Here we address how to control the variance in allele frequency estimation when DNAs are pooled, and how to plan and conduct the most efficient well-powered pool-based GWAS.</p> <p>Methods</p> <p>By examining the variation in allele frequency estimation on SNP arrays between and within DNA pools we determine how array variance [var(e<sub>array</sub>)] and pool-construction variance [var(e<sub>construction</sub>)] contribute to the total variance of allele frequency estimation. This information is useful in deciding whether replicate arrays or replicate pools are most useful in reducing variance. Our analysis is based on 27 DNA pools ranging in size from 74 to 446 individual samples, genotyped on a collective total of 128 Illumina beadarrays: 24 1M-Single, 32 1M-Duo, and 72 660-Quad.</p> <p>Results</p> <p>For all three Illumina SNP array types our estimates of var(e<sub>array</sub>) were similar, between 3-4 Ă— 10<sup>-4 </sup>for normalized data. Var(e<sub>construction</sub>) accounted for between 20-40% of pooling variance across 27 pools in normalized data.</p> <p>Conclusions</p> <p>We conclude that relative to var(e<sub>array</sub>), var(e<sub>construction</sub>) is of less importance in reducing the variance in allele frequency estimation from DNA pools; however, our data suggests that on average it may be more important than previously thought. We have prepared a simple online tool, PoolingPlanner (available at <url>http://www.kchew.ca/PoolingPlanner/</url>), which calculates the effective sample size (ESS) of a DNA pool given a range of replicate array values. ESS can be used in a power calculator to perform pool-adjusted calculations. This allows one to quickly calculate the loss of power associated with a pooling experiment to make an informed decision on whether a pool-based GWAS is worth pursuing.</p
Genetic Admixture and Population Substructure in Guanacaste Costa Rica
The population of Costa Rica (CR) represents an admixture of major continental populations. An investigation of the CR population structure would provide an important foundation for mapping genetic variants underlying common diseases and traits. We conducted an analysis of 1,301 women from the Guanacaste region of CR using 27,904 single nucleotide polymorphisms (SNPs) genotyped on a custom Illumina InfiniumII iSelect chip. The program STRUCTURE was used to compare the CR Guanacaste sample with four continental reference samples, including HapMap Europeans (CEU), East Asians (JPT+CHB), West African Yoruba (YRI), as well as Native Americans (NA) from the Illumina iControl database. Our results show that the CR Guanacaste sample comprises a three-way admixture estimated to be 43% European, 38% Native American and 15% West African. An estimated 4% residual Asian ancestry may be within the error range. Results from principal components analysis reveal a correlation between genetic and geographic distance. The magnitude of linkage disequilibrium (LD) measured by the number of tagging SNPs required to cover the same region in the genome in the CR Guanacaste sample appeared to be weaker than that observed in CEU, JPT+CHB and NA reference samples but stronger than that of the HapMap YRI sample. Based on the clustering pattern observed in both STRUCTURE and principal components analysis, two subpopulations were identified that differ by approximately 20% in LD block size averaged over all LD blocks identified by Haploview. We also show in a simulated association study conducted within the two subpopulations, that the failure to account for population stratification (PS) could lead to a noticeable inflation in the false positive rate. However, we further demonstrate that existing PS adjustment approaches can reduce the inflation to an acceptable level for gene discovery
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