1,646 research outputs found
Measuring orbital angular momentum superpositions of light by mode transformation
We recently reported on a method for measuring orbital angular momentum (OAM) states of light based on the transformation of helically phased beams to tilted plane waves [Phys. Rev. Lett.105, 153601 (2010)]. Here we consider the performance of such a system for superpositions of OAM states by measuring the modal content of noninteger OAM states and beams produced by a Heaviside phase plate
Divergence of an orbital-angular-momentum-carrying beam upon propagation
There is recent interest in the use of light beams carrying orbital angular
momentum (OAM) for creating multiple channels within free-space optical
communication systems. One limiting issue is that, for a given beam size at the
transmitter, the beam divergence angle increases with increasing OAM, thus
requiring a larger aperture at the receiving optical system if the efficiency
of detection is to be maintained. Confusion exists as to whether this
divergence scales linarly with, or with the square root of, the beam's OAM. We
clarify how both these scaling laws are valid, depending upon whether it is the
radius of the Gaussian beam waist or the rms intensity which is kept constant
while varying the OAM.Comment: 4 pages, 2 figure
Direct Measurement of a 27-Dimensional Orbital-Angular-Momentum State Vector
The measurement of a quantum state poses a unique challenge for
experimentalists. Recently, the technique of "direct measurement" was proposed
for characterizing a quantum state in-situ through sequential weak and strong
measurements. While this method has been used for measuring polarization
states, its real potential lies in the measurement of states with a large
dimensionality. Here we show the practical direct measurement of a
high-dimensional state vector in the discrete basis of orbital-angular
momentum. Through weak measurements of orbital-angular momentum and strong
measurements of angular position, we measure the complex probability amplitudes
of a pure state with a dimensionality, d=27. Further, we use our method to
directly observe the relationship between rotations of a state vector and the
relative phase between its orbital-angular-momentum components. Our technique
has important applications in high-dimensional classical and quantum
information systems, and can be extended to characterize other types of large
quantum states.Comment: 8 pages, 3 figure
Influence of Atmospheric Turbulence on Optical Communications using Orbital Angular Momentum for Encoding
We describe an experimental implementation of a free-space 11-dimensional
communication system using orbital angular momentum (OAM) modes. This system
has a maximum measured OAM channel capacity of 2.12 bits/photon. The effects of
Kolmogorov thin-phase turbulence on the OAM channel capacity are quantified. We
find that increasing the turbulence leads to a degradation of the channel
capacity. We are able to mitigate the effects of turbulence by increasing the
spacing between detected OAM modes. This study has implications for
high-dimensional quantum key distribution (QKD) systems. We describe the sort
of QKD system that could be built using our current technology.Comment: 6 pages, 5 figure
Free-space propagation of high dimensional structured optical fields in an urban environment
Spatially structured optical fields have been used to enhance the functionality of a wide variety of systems that use
light for sensing or information transfer. As higher-dimensional modes become a solution of choice in optical
systems, it is important to develop channel models that suitably predict the effect of atmospheric turbulence on
these modes. We investigate the propagation of a set of orthogonal spatial modes across a free-space channel
between two buildings separated by 1.6 km. Given the circular geometry of a common optical lens, the orthogonal
mode set we choose to implement is that described by the Laguerre-Gaussian (LG) field equations. Our study focuses
on the preservation of phase purity, which is vital for spatial multiplexing and any system requiring full quantumstate
tomography. We present experimental data for the modal degradation in a real urban environment and draw a
comparison to recognized theoretical predictions of the link. Our findings indicate that adaptations to channel
models are required to simulate the effects of atmospheric turbulence placed on high-dimensional structured
modes that propagate over a long distance. Our study indicates that with mitigation of vortex splitting, potentially
through precorrection techniques, one could overcome the challenges in a real point-to-point free-space channel in
an urban environment
Trypanosoma cruzi IIc: phylogenetic and phylogeographic insights from sequence and microsatellite analysis and potential impact on emergent Chagas disease.
Trypanosoma cruzi, the etiological agent of Chagas disease, is highly genetically diverse. Numerous lines of evidence point to the existence of six stable genetic lineages or DTUs: TcI, TcIIa, TcIIb, TcIIc, TcIId, and TcIIe. Molecular dating suggests that T. cruzi is likely to have been an endemic infection of neotropical mammalian fauna for many millions of years. Here we have applied a panel of 49 polymorphic microsatellite markers developed from the online T. cruzi genome to document genetic diversity among 53 isolates belonging to TcIIc, a lineage so far recorded almost exclusively in silvatic transmission cycles but increasingly a potential source of human infection. These data are complemented by parallel analysis of sequence variation in a fragment of the glucose-6-phosphate isomerase gene. New isolates confirm that TcIIc is associated with terrestrial transmission cycles and armadillo reservoir hosts, and demonstrate that TcIIc is far more widespread than previously thought, with a distribution at least from Western Venezuela to the Argentine Chaco. We show that TcIIc is truly a discrete T. cruzi lineage, that it could have an ancient origin and that diversity occurs within the terrestrial niche independently of the host species. We also show that spatial structure among TcIIc isolates from its principal host, the armadillo Dasypus novemcinctus, is greater than that among TcI from Didelphis spp. opossums and link this observation to differences in ecology of their respective niches. Homozygosity in TcIIc populations and some linkage indices indicate the possibility of recombination but cannot yet be effectively discriminated from a high genome-wide frequency of gene conversion. Finally, we suggest that the derived TcIIc population genetic data have a vital role in determining the origin of the epidemiologically important hybrid lineages TcIId and TcIIe
Photon efficient wavefront sensing using an SLM for polarization-based weak measurements
A novel scheme is proposed for two dimensional direct measurement of wave functions using an SLM. This photon efficient method can be potentially useful for wavefront sensing of turbulence in adaptive optics systems used in free-space communication systems
Thermal reaction norms and the scale of temperature variation: latitudinal vulnerability of intertidal Nacellid limpets to climate change
The thermal reaction norms of 4 closely related intertidal Nacellid limpets, Antarctic (Nacella concinna), New Zealand (Cellana ornata), Australia (C. tramoserica) and Singapore (C. radiata), were compared across environments with different temperature magnitude, variability and predictability, to test their relative vulnerability to different scales of climate warming. Lethal limits were measured alongside a newly developed metric of “duration tenacity”, which was tested at different temperatures to calculate the thermal reaction norm of limpet adductor muscle fatigue. Except in C. tramoserica which had a wide optimum range with two break points, duration tenacity did not follow a typical aerobic capacity curve but was best described by a single break point at an optimum temperature. Thermal reaction norms were shifted to warmer temperatures in warmer environments; the optimum temperature for tenacity (Topt) increased from 1.0°C (N. concinna) to 14.3°C (C. ornata) to 18.0°C (an average for the optimum range of C. tramoserica) to 27.6°C (C. radiata). The temperature limits for duration tenacity of the 4 species were most consistently correlated with both maximum sea surface temperature and summer maximum in situ habitat logger temperature. Tropical C. radiata, which lives in the least variable and most predictable environment, generally had the lowest warming tolerance and thermal safety margin (WT and TSM; respectively the thermal buffer of CTmax and Topt over habitat temperature). However, the two temperate species, C. ornata and C. tramoserica, which live in a variable and seasonally unpredictable microhabitat, had the lowest TSM relative to in situ logger temperature. N. concinna which lives in the most variable, but seasonally predictable microhabitat, generally had the highest TSMs. Intertidal animals live at the highly variable interface between terrestrial and marine biomes and even small changes in the magnitude and predictability of their environment could markedly influence their future distributions
High-dimensional quantum cryptography with twisted light
Quantum key distributions (QKD) systems often rely on polarization of light
for encoding, thus limiting the amount of information that can be sent per
photon and placing tight bounds on the error that such a system can tolerate.
Here we describe a proof-of-principle experiment that indicates the feasibility
of high-dimensional QKD based on the transverse structure of the light field,
allowing for the transfer of more than 1 bit per photon. Our implementation
uses the orbital angular momentum (OAM) of photons and the corresponding
mutually unbiased basis of angular position (ANG). Our experiment uses a
digital micro-mirror device for the rapid generation of OAM and ANG modes at 4
kHz, and a mode sorter capable of sorting single photons based on their OAM and
ANG content with a separation efficiency of 93\%. Through the use of a
7-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel
capacity of 2.05 bits per sifted photon. Our experiment shows that, in addition
to having an increased information capacity, QKD systems based on spatial-mode
encoding will be more tolerant to errors and thus more robust against
eavesdropping attacks
Two centuries of southwest Iceland annually-resolved marine temperature reconstructed from Arctica islandica shells
Iceland's exposure to major ocean current pathways of the central North Atlantic makes it a useful location for developing long-term proxy records of past marine climate. Such records provide more detailed understanding of the full range of past variability which is necessary to improve predictions of future changes. We constructed a 225-year (1791–2015 CE) master shell growth chronology from 29 shells of Arctica islandica collected at 100 m water depth in southwest Iceland (Faxaflói). The growth chronology provides a robust age model for shell oxygen isotope (δ18Oshell) data produced at annual resolution for 251 years (1765–2015 CE). The temperature reconstruction derived from δ18Oshell shows coherence with May–October local surface temperature records and sea surface temperatures in the North Atlantic region, suggesting it is a useful proxy indicator of water temperature variability at 100 m depth within Faxaflói. Field correlations between the shell-based records and gridded sea surface temperature data reveal strong positive correlations between the 1-year lagged shell growth and temperatures within the subpolar gyre post-1972, suggesting a delayed influence of subpolar gyre dynamics on ecological indicators in southwest Iceland in recent decades. However, the shell growth chronology and δ18Oshell record generally show relatively weak and insignificant correlations with larger region climate indices including the Atlantic Multidecadal Variability, North Atlantic Oscillation, and East Atlantic pattern. Therefore the interannual variations in the newly produced shell-based records appear to reflect more local to regional dynamics around southwest Iceland than large-scale modes of climate variability.publishedVersio
- …