95 research outputs found
Spectral Effects of Strong Chi-2 Non-Linearity for Quantum Processing
Optical non-linearity can be used for parametric amplification
and producing down-converted entangled photon pairs that have broad
applications. It is known that weak non-linear media exhibit dispersion and
produce a frequency response. It is therefore of interest to know how spectral
effects of a strong crystal affect the performance. Here we model
the spectral effects of the dispersion of a strong crystal and
illustrate how this affects its ability to perform Bell measurements and
influence the performance of a quantum gates that employ such a Bell
measurement. We show that a Dyson series expansion of the unitary operator is
necessary in general, leading to unwanted spectral entanglement. We identify a
limiting situation employing periodic poling, in which a Taylor series
expansion is a good approximation and this entanglement can be removed.Comment: Will be submitted to PR
Indistinguishability of independent single photons
The indistinguishability of independent single photons is presented by
decomposing the single photon pulse into the mixed state of different transform
limited pulses. The entanglement between single photons and outer environment
or other photons induces the distribution of the center frequencies of those
transform limited pulses and makes photons distinguishable. Only the single
photons with the same transform limited form are indistinguishable. In details,
the indistinguishability of single photons from the solid-state quantum emitter
and spontaneous parametric down conversion is examined with two-photon
Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the
indistinguishability are discussed, where the usage of spectral filter is
highlighted.Comment: 6 pages, 3 figure
Continuous-variable optical quantum state tomography
This review covers latest developments in continuous-variable quantum-state
tomography of optical fields and photons, placing a special accent on its
practical aspects and applications in quantum information technology. Optical
homodyne tomography is reviewed as a method of reconstructing the state of
light in a given optical mode. A range of relevant practical topics are
discussed, such as state-reconstruction algorithms (with emphasis on the
maximum-likelihood technique), the technology of time-domain homodyne
detection, mode matching issues, and engineering of complex quantum states of
light. The paper also surveys quantum-state tomography for the transverse
spatial state (spatial mode) of the field in the special case of fields
containing precisely one photon.Comment: Finally, a revision! Comments to lvov(at)ucalgary.ca and
raymer(at)uoregon.edu are welcom
Pure-state single-photon wave-packet generation by parametric down conversion in a distributed microcavity
We propose an optical parametric down conversion (PDC) scheme that does not
suffer a trade-off between the state-purity of single-photon wave-packets and
the rate of packet production. This is accomplished by modifying the PDC
process by using a microcavity to engineer the density of states of the optical
field at the PDC frequencies. The high-finesse cavity mode occupies a spectral
interval much narrower than the bandwidth of the pulsed pump laser field,
suppressing the spectral correlation, or entanglement, between signal and idler
photons. Spectral filtering of the field occurs prior to photon creation rather
than afterward as in most other schemes. Operator-Maxwell equations are solved
to find the Schmidt-mode decomposition of the two-photon states produced.
Greater than 99% pure-state packet production is predicted to be achievable.Comment: submitted for publicatio
Complete characterization of weak, ultrashort near-UV pulses by spectral interferometry
We present a method for a complete characterization of a femtosecond
ultraviolet pulse when a fundamental near-infrared beam is also available. Our
approach relies on generation of second harmonic from the pre-characterized
fundamental, which serves as a reference against which an unknown pulse is
measured using spectral interference (SI). The characterization apparatus is a
modified second harmonic frequency resolved optical gating setup which
additionally allows for taking SI spectrum. The presented method is linear in
the unknown field, simple and sensitive. We checked its accuracy using test
pulses generated in a thick nonlinear crystal, demonstrating the ability to
measure the phase in a broad spectral range, down to 0.1% peak spectral
intensity as well as retrieving pi leaps in the spectral phase
Review article: Linear optical quantum computing
Linear optics with photon counting is a prominent candidate for practical
quantum computing. The protocol by Knill, Laflamme, and Milburn [Nature 409, 46
(2001)] explicitly demonstrates that efficient scalable quantum computing with
single photons, linear optical elements, and projective measurements is
possible. Subsequently, several improvements on this protocol have started to
bridge the gap between theoretical scalability and practical implementation. We
review the original theory and its improvements, and we give a few examples of
experimental two-qubit gates. We discuss the use of realistic components, the
errors they induce in the computation, and how these errors can be corrected.Comment: 41 pages, 37 figures, many small changes, added references, and
improved discussion on error correction and fault toleranc
Fungal endophytes from arid areas of Andalusia: high potential sources for antifungal and antitumoral agents
Native plant communities from arid areas present distinctive characteristics to survive in extreme
conditions. The large number of poorly studied endemic plants represents a unique potential
source for the discovery of novel fungal symbionts as well as host-specific endophytes not yet
described. The addition of adsorptive polymeric resins in fungal fermentations has been seen to
promote the production of new secondary metabolites and is a tool used consistently to generate
new compounds with potential biological activities. A total of 349 fungal strains isolated from 63
selected plant species from arid ecosystems located in the southeast of the Iberian Peninsula, were
characterized morphologically as well as based on their ITS/28S ribosomal gene sequences. The fungal
community isolated was distributed among 19 orders including Basidiomycetes and Ascomycetes,
being Pleosporales the most abundant order. In total, 107 different genera were identified being
Neocamarosporium the genus most frequently isolated from these plants, followed by Preussia and
Alternaria. Strains were grown in four different media in presence and absence of selected resins to
promote chemical diversity generation of new secondary metabolites. Fermentation extracts were
evaluated, looking for new antifungal activities against plant and human fungal pathogens, as well
as, cytotoxic activities against the human liver cancer cell line HepG2. From the 349 isolates tested,
126 (36%) exhibited significant bioactivities including 58 strains with exclusive antifungal properties
and 33 strains with exclusive activity against the HepG2 hepatocellular carcinoma cell line. After LCMS
analysis, 68 known bioactive secondary metabolites could be identified as produced by 96 strains,
and 12 likely unknown compounds were found in a subset of 14 fungal endophytes. The chemical
profiles of the differential expression of induced activities were compared. As proof of concept, ten
active secondary metabolites only produced in the presence of resins were purified and identified. The
structures of three of these compounds were new and herein are elucidated.This work was supported by Fundación MEDINA and the Andalusian Government grant
RNM-7987 ‘Sustainable use of plants and their fungal parasites from arid regions of Andalucía for new molecules
useful for antifungals and neuroprotectors’
A window into fungal endophytism in Salicornia europaea: deciphering fungal characteristics as plant growth promoting agents
Aim Plant-endophytic associations exist only when equilibrium is maintained between both partners. This study analyses the properties of endophytic fungi
inhabiting a halophyte growing in high soil salinity and tests whether these fungi are beneficial or detrimental when non-host plants are inoculated.
Method Fungi were isolated from Salicornia europaea collected from two sites differing in salinization history (anthropogenic and naturally saline) and analyzed for plant growth promoting abilities and non-host plant interactions.
Results Most isolated fungi belonged to Ascomycota (96%) including dematiaceous fungi and commonly known plant pathogens and saprobes. The strains were
metabolically active for siderophores, polyamines and indole-3-acetic acid (mainly Aureobasidium sp.) with very low activity for phosphatases. Many showed proteolytic, lipolytic, chitinolytic, cellulolytic and amylolytic activities but low pectolytic activity. Different activities between similar fungal species found in both sites were particularly seen for Epiccocum sp., Arthrinium sp. and
Trichoderma sp. Inoculating the non-host Lolium perenne with selected fungi increased plant growth, mainly in the symbiont (Epichloë)-free variety.
Arthrinium gamsii CR1-9 and Stereum gausapatum ISK3-11 were most effective for plant growth promotion.
Conclusions This research suggests that host lifestyle and soil characteristics have a strong effect on endophytic fungi, and environmental stress could disturb the
plant-fungi relations. In favourable conditions, these fungi may be effective in facilitating crop production in non-cultivable saline lands
Evolution of Burkholderia pseudomallei in Recurrent Melioidosis
Burkholderia pseudomallei, the etiologic agent of human melioidosis, is capable of causing severe acute infection with overwhelming septicemia leading to death. A high rate of recurrent disease occurs in adult patients, most often due to recrudescence of the initial infecting strain. Pathogen persistence and evolution during such relapsing infections are not well understood. Bacterial cells present in the primary inoculum and in late infections may differ greatly, as has been observed in chronic disease, or they may be genetically similar. To test these alternative models, we conducted whole-genome comparisons of clonal primary and relapse B. pseudomallei isolates recovered six months to six years apart from four adult Thai patients. We found differences within each of the four pairs, and some, including a 330 Kb deletion, affected substantial portions of the genome. Many of the changes were associated with increased antibiotic resistance. We also found evidence of positive selection for deleterious mutations in a TetR family transcriptional regulator from a set of 107 additional B. pseudomallei strains. As part of the study, we sequenced to base-pair accuracy the genome of B. pseudomallei strain 1026b, the model used for genetic studies of B. pseudomallei pathogenesis and antibiotic resistance. Our findings provide new insights into pathogen evolution during long-term infections and have important implications for the development of intervention strategies to combat recurrent melioidosis
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