94 research outputs found
Sampling Bias Overestimates Climate Change Impacts on Forest Growth in the Southwestern United States
Climate−tree growth relationships recorded in annual growth rings have recently been the basis for projecting climate change impacts on forests. However, most trees and sample sites represented in the International Tree-Ring Data Bank (ITRDB) were chosen to maximize climate signal and are characterized by marginal growing conditions not representative of the larger forest ecosystem. We evaluate the magnitude of this potential bias using a spatially unbiased tree-ring network collected by the USFS Forest Inventory and Analysis (FIA) program. We show that U.S. Southwest ITRDB samples overestimate regional forest climate sensitivity by 41–59%, because ITRDB trees were sampled at warmer and drier locations, both at the macro- and micro-site scale, and are systematically older compared to the FIA collection. Although there are uncertainties associated with our statistical approach, projection based on representative FIA samples suggests 29% less of a climate change-induced growth decrease compared to projection based on climate-sensitive ITRDB samples
Metropolitan quantum key distribution with silicon photonics
Photonic integrated circuits (PICs) provide a compact and stable platform for
quantum photonics. Here we demonstrate a silicon photonics quantum key
distribution (QKD) transmitter in the first high-speed polarization-based QKD
field tests. The systems reach composable secret key rates of 950 kbps in a
local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 106
kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss).
Our results represent the highest secret key generation rate for
polarization-based QKD experiments at a standard telecom wavelength and
demonstrate PICs as a promising, scalable resource for future formation of
metropolitan quantum-secure communications networks
High Speed Travelling Wave Carrier Depletion Silicon Mach-Zehnder Modulator
Abstract: We present the first demonstration of a travelling wave carrier depletion Mach-Zehnder modulator impedance matched to 50 : This device has a bandwidth of 24 GHz and a halfwave voltage length product of 0.7 V-cm, placing it among the best in its class
Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere
Motivated by the recognition that variation in the optical transmission of
the atmosphere is probably the main limitation to the precision of ground-based
CCD measurements of celestial fluxes, we review the physical processes that
attenuate the passage of light through the Earth's atmosphere. The next
generation of astronomical surveys, such as PanSTARRS and LSST, will greatly
benefit from dedicated apparatus to obtain atmospheric transmission data that
can be associated with each survey image. We review and compare various
approaches to this measurement problem, including photometry, spectroscopy, and
LIDAR. In conjunction with careful measurements of instrumental throughput,
atmospheric transmission measurements should allow next-generation imaging
surveys to produce photometry of unprecedented precision. Our primary concerns
are the real-time determination of aerosol scattering and absorption by water
along the line of sight, both of which can vary over the course of a night's
observations.Comment: 41 pages, 14 figures. Accepted PAS
High-Performance Silicon Photonic Single-Sideband Modulators for Cold Atom Interferometry
The most complicated and challenging system within a light-pulse atom
interferometer (LPAI) is the laser system, which controls the frequencies and
intensities of multiple laser beams over time to configure quantum gravity and
inertial sensors. The main function of an LPAI laser system is to perform
cold-atom generation and state-selective detection and to generate coherent
two-photon process for the light-pulse sequence. Substantial miniaturization
and ruggedization of the laser system can be achieved by bringing together most
key functions of the laser and optical system onto a photonic integrated
circuit (PIC). Here we demonstrate a high-performance silicon photonic
carrier-suppressed single-sideband (CS-SSB) modulator PIC with dual-parallel
Mach-Zehnder modulators (DP-MZMs) operating near 1560 nm, which can dynamically
shift the frequency of the light for the desired function within the LPAI.
Independent RF control of channels in SSB modulator enables the extensive study
of imbalances in both the optical and RF phases and amplitudes to
simultaneously reach 30 dB carrier suppression and unprecedented 47.8 dB
sideband suppression with peak conversion efficiency of -6.846 dB (20.7 %).
Using a silicon photonic SSB modulator with time-multiplexed frequency shifting
in an LPAI laser system, we demonstrate cold-atom generation, state-selective
detection, and the realization of atom interferometer fringes to estimate
gravitational acceleration, , in a
Rubidium (Rb) atom system.Comment: 18 pages, 9 figure
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