50 research outputs found
Photon pair-state preparation with tailored spectral properties by spontaneous four-wave mixing in photonic-crystal fiber
We study theoretically the generation of photon pairs by spontaneous
four-wave mixing (SFWM) in photonic crystal optical fiber. We show that it is
possible to engineer two-photon states with specific spectral correlation
(``entanglement'') properties suitable for quantum information processing
applications. We focus on the case exhibiting no spectral correlations in the
two-photon component of the state, which we call factorability, and which
allows heralding of single-photon pure-state wave packets without the need for
spectral post filtering. We show that spontaneous four wave mixing exhibits a
remarkable flexibility, permitting a wider class of two-photon states,
including ultra-broadband, highly-anticorrelated states.Comment: 17 pages, 7 figures, submitte
From quantum pulse gate to quantum pulse shaper -- enigneered frequency conversion in nonlinear optical waveguides
Full control over the spatio-temporal structure of quantum states of light is
an important goal in quantum optics, to generate for instance single-mode
quantum pulses or to encode information on multiple modes, enhancing channel
capacities. Quantum light pulses feature an inherent, rich spectral
broadband-mode structure. In recent years, exploring the use of integrated
optics as well as source-engineering has led to a deep understanding of the
pulse-mode structure of guided quantum states of light. In addition, several
groups have started to investigate the manipulation of quantum states by means
of single-photon frequency conversion. In this paper we explore new routes
towards complete control of the inherent pulse-modes of ultrafast pulsed
quantum states by employing specifically designed nonlinear waveguides with
adapted dispersion properties. Starting from our recently proposed quantum
pulse gate (QPG) we further generalize the concept of spatio-spectral
engineering for arbitrary \chitwo-based quantum processes. We analyse the
sum-frequency generation based QPG and introduce the difference-frequency
generation based quantum pulse shaper (QPS). Together, these versatile and
robust integrated optics devices allow for arbitrary manipulations of the
pulse-mode structure of ultrafast pulsed quantum states. The QPG can be
utilized to select an arbitrary pulse mode from a multimode input state,
whereas the QPS enables the generation of specific pulse modes from an input
wavepacket with Gaussian-shaped spectrum.Comment: 21 pages, 9 figure
Optimised generation of heralded Fock states using parametric down conversion
The generation of heralded pure Fock states via spontaneous parametric down
conversion (PDC) relies on perfect photon-number correlations in the output
modes. Correlations in any other degree of freedom, however, degrade the purity
of the heralded state. In this paper, we investigate spectral entanglement
between the two output modes of a periodically poled waveguide. With the intent
of generating heralded 1- and 2-photon Fock states, we expand the output state
of the PDC to second order in photon number. We explore the effects of spectral
filtering and inefficient detection, of the heralding mode, on the count rate,
g(2) and purity of the heralded state, as well as the fidelity between the
resulting state and an ideal Fock state. We find that filtering can decrease
spectral correlations, however, at the expense of the count rate and increased
photon-number mixedness in the heralded output state. As a physical example, we
model a type II PP-KTP waveguide pumped by lasers at wavelengths of 400 nm, 788
nm and 1930 nm. The latter two allow the fulfillment of extended phase matching
conditions in an attempt to eliminate spectral correlations in the PDC output
state without the use of filtering, however, we find that even in these cases,
some filtering is needed to achieve states of very high purity.Comment: 28 pages, 25 figures, revised expressions for two-photon fidelit
Avalanche Photo-Detection for High Data Rate Applications
Avalanche photo detection is commonly used in applications which require
single photon sensitivity. We examine the limits of using avalanche photo
diodes (APD) for characterising photon statistics at high data rates. To
identify the regime of linear APD operation we employ a ps-pulsed diode laser
with variable repetition rates between 0.5MHz and 80MHz. We modify the mean
optical power of the coherent pulses by applying different levels of
well-calibrated attenuation. The linearity at high repetition rates is limited
by the APD dead time and a non-linear response arises at higher photon-numbers
due to multiphoton events. Assuming Poissonian input light statistics we
ascertain the effective mean photon-number of the incident light with high
accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number
resolution by photon chopping. This detection setup extends the linear response
function to higher photon-numbers and statistical methods may be used to
compensate for non-linearity. We investigated this effect, compare it to the
single APD case and show the validity of the convolution treatment in the TMD
data analysis.Comment: 16 pages, 5 figure
Demonstration of Controllable Temporal Distinguishability in a Three-Photon State
Multi-photon interference is at the heart of the recently proposed linear
optical quantum computing scheme and plays an essential role in many protocols
in quantum information. Indistinguishability is what leads to the effect of
quantum interference. Optical interferometers such as Michaelson interferometer
provide a measure for second-order coherence at one-photon level and
Hong-Ou-Mandel interferometer was widely employed to describe two-photon
entanglement and indistinguishability. However, there is not an effective way
for a system of more than two photons. Recently, a new interferometric scheme
was proposed to quantify the degree of multi-photon distinguishability. Here we
report an experiment to implement the scheme for three-photon case. We are able
to generate three photons with different degrees of temporal distinguishability
and demonstrate how to characterize them by the visibility of three-photon
interference. This method of quantitative description of multi-photon
indistinguishability will have practical implications in the implementation of
quantum information protocols
Experiential learning and the acquisition of managerial tacit knowledge
Tacit knowledge is believed to be one factor that distinguishes successful managers from others. We sought to determine whether levels of accumulated managerial tacit knowledge (LAMTK) were associated with managers' dominant learning styles. Instruments used in the study, involving 356 Malaysian public sector employees, included Sternberg et al.'s (2000) Tacit Knowledge Inventory for Managers and a normative version of Kolb's (1999a) Learning Styles Inventory (LSI-Ill). Findings suggest that LAMTK is independent of the length of subjects' general work experience, but positively related to the amount of time spent working in a management context. Learning styles also had a significant relationship. Subjects who spent most of their time performing management functions and whose dominant learning styles were accommodating had significantly higher LAMTK than those with different learning styles. We also found support for the belief that learners with a strong preference for all four different abilities defined in Kolb's learning theory may be critical for effective experiential learning
BurkDiff: A Real-Time PCR Allelic Discrimination Assay for Burkholderia Pseudomallei and B. mallei
A real-time PCR assay, BurkDiff, was designed to target a unique conserved region in the B. pseudomallei and B. mallei genomes containing a SNP that differentiates the two species. Sensitivity and specificity were assessed by screening BurkDiff across 469 isolates of B. pseudomallei, 49 isolates of B. mallei, and 390 isolates of clinically relevant non-target species. Concordance of results with traditional speciation methods and no cross-reactivity to non-target species show BurkDiff is a robust, highly validated assay for the detection and differentiation of B. pseudomallei and B. mallei
Within-Host Evolution of Burkholderia pseudomallei in Four Cases of Acute Melioidosis
Little is currently known about bacterial pathogen evolution and adaptation within the host during acute infection. Previous studies of Burkholderia pseudomallei, the etiologic agent of melioidosis, have shown that this opportunistic pathogen mutates rapidly both in vitro and in vivo at tandemly repeated loci, making this organism a relevant model for studying short-term evolution. In the current study, B. pseudomallei isolates cultured from multiple body sites from four Thai patients with disseminated melioidosis were subjected to fine-scale genotyping using multilocus variable-number tandem repeat analysis (MLVA). In order to understand and model the in vivo variable-number tandem repeat (VNTR) mutational process, we characterized the patterns and rates of mutations in vitro through parallel serial passage experiments of B. pseudomallei. Despite the short period of infection, substantial divergence from the putative founder genotype was observed in all four melioidosis cases. This study presents a paradigm for examining bacterial evolution over the short timescale of an acute infection. Further studies are required to determine whether the mutational process leads to phenotypic alterations that impact upon bacterial fitness in vivo. Our findings have important implications for future sampling strategies, since colonies in a single clinical sample may be genetically heterogeneous, and organisms in a culture taken late in the infective process may have undergone considerable genetic change compared with the founder inoculum
Gene Expression Profiles of Sporadic Canine Hemangiosarcoma Are Uniquely Associated with Breed
The role an individual's genetic background plays on phenotype and biological behavior of sporadic tumors remains incompletely understood. We showed previously that lymphomas from Golden Retrievers harbor defined, recurrent chromosomal aberrations that occur less frequently in lymphomas from other dog breeds, suggesting spontaneous canine tumors provide suitable models to define how heritable traits influence cancer genotypes. Here, we report a complementary approach using gene expression profiling in a naturally occurring endothelial sarcoma of dogs (hemangiosarcoma). Naturally occurring hemangiosarcomas of Golden Retrievers clustered separately from those of non-Golden Retrievers, with contributions from transcription factors, survival factors, and from pro-inflammatory and angiogenic genes, and which were exclusively present in hemangiosarcoma and not in other tumors or normal cells (i.e., they were not due simply to variation in these genes among breeds). Vascular Endothelial Growth Factor Receptor 1 (VEGFR1) was among genes preferentially enriched within known pathways derived from gene set enrichment analysis when characterizing tumors from Golden Retrievers versus other breeds. Heightened VEGFR1 expression in these tumors also was apparent at the protein level and targeted inhibition of VEGFR1 increased proliferation of hemangiosarcoma cells derived from tumors of Golden Retrievers, but not from other breeds. Our results suggest heritable factors mold gene expression phenotypes, and consequently biological behavior in sporadic, naturally occurring tumors