1,814 research outputs found
Bright source of spectrally uncorrelated polarization-entangled photons with nearly single-mode emission
We present results of a bright polarization-entangled photon source operating
at 1552 nm via type-II collinear degenerate spontaneous parametric
down-conversion in a periodically poled potassium titanyl phosphate crystal. We
report a conservative inferred pair generation rate of 123,000 pairs/s/mW into
collection modes. Minimization of spectral and spatial entanglement was
achieved by group velocity matching the pump, signal and idler modes and
through properly focusing the pump beam. By utilizing a pair of calcite beam
displacers, we are able to overlap photons from adjacent down-conversion
processes to obtain polarization-entanglement visibility of 94.7 +/- 1.1% with
accidentals subtracted.Comment: 4 pages, 7 color figures. Revised manuscript includes the following
changes: corrected pair generation rate from 44,000/s/mW pump to 123,000/s/mW
pump; replaced Fig. 1b to enhance clarity; minor alterations to the title,
abstract and introduction; grammatical correction
Novel Cascaded Ultra Bright Pulsed Source of Polarization Entangled Photons
A new ultra bright pulsed source of polarization entangled photons has been
realized using type-II phase matching in spontaneous parametric down conversion
process in two cascaded crystals. The optical axes of the crystals are aligned
in such a way that the extraordinarily (ordinarily) polarized cone from one
crystal overlaps with the ordinarily (extraordinarily) polarized cone from the
second crystal. This spatial overlapping removes the association between the
polarization and the output angle of the photons that exist in a single type-II
down conversion process. Hence, entanglement of photons originating from any
point on the output cones is possible if a suitable optical delay line is used.
This delay line is particularly simple and easy to implement.Comment: 8 pages 8 figure
Atlas.txt : Exploring Lingusitic Grounding Techniques for Communicating Spatial Information to Blind Users
Peer reviewedPostprin
A growing disconnection from nature is evident in cultural products
Human connection with nature is widely believed to be in decline, even though empirical evidence on the magnitude and temporal pattern of the change is scarce. Studying works of popular culture in English throughout the 20th century and later, we document a cultural shift away from nature, beginning in the 1950s. Since then, references to nature have been decreasing steadily in fiction, song lyrics, and film storylines. No parallel decline is observed in references to the human-made environment. These findings are cause for concern, not only because they imply foregone benefits from engagement with nature, but also because cultural products are agents of socialization that can evoke curiosity, respect, and concern for the natural world
Bell State Preparation using Pulsed Non-Degenerate Two-Photon Entanglement
We report a novel Bell state preparation experiment. High-purity Bell states
are prepared by using femtosecond pulse pumped \emph{nondegenerate} collinear
spontaneous parametric down-conversion. The use of femtosecond pump pulse {\em
does not} result in reduction of quantum interference visibility in our scheme
in which post-selection of amplitudes and other traditional mechanisms, such
as, using thin nonlinear crystals or narrow-band spectral filters are not used.
Another distinct feature of this scheme is that the pump, the signal, and the
idler wavelengths are all distinguishable, which is very useful for quantum
communications.Comment: 4 pages, submitted to PR
Ribonuclease H/DNA polymerase HIV-1 reverse transcriptase dual inhibitor: mechanistic studies on the allosteric mode of action of isatin-based compound RMNC6
The DNA polymerase and ribonuclease H (RNase H) activities of human immunodeficiency virus type 1 (HIV-1) are needed for the replication of the viral genome and are validated drug targets. However, there are no approved drugs inhibiting RNase H and the efficiency of DNA polymerase inhibitors can be diminished by the presence of drug resistance mutations. In this context, drugs inhibiting both activities could represent a significant advance towards better anti-HIV therapies. We report on the mechanisms of allosteric inhibition of a newly synthesized isatin-based compound designated as RMNC6 that showed IC50 values of 1.4 and 9.8 ÎŒM on HIV-1 RT-associated RNase H and polymerase activities, respectively. Blind docking studies predict that RMNC6 could bind two different pockets in the RT: one in the DNA polymerase domain (partially overlapping the non-nucleoside RT inhibitor [NNRTI] binding pocket), and a second one close to the RNase H active site. Enzymatic studies showed that RMNC6 interferes with efavirenz (an approved NNRTI) in its binding to the RT polymerase domain, although NNRTI resistance-associated mutations such as K103N, Y181C and Y188L had a minor impact on RT susceptibility to RMNC6. In addition, despite being naturally resistant to NNRTIs, the polymerase activity of HIV-1 group O RT was efficiently inhibited by RMNC6. The compound was also an inhibitor of the RNase H activity of wild-type HIV-1 group O RT, although we observed a 6.5-fold increase in the IC50 in comparison with the prototypic HIV-1 group M subtype B enzyme. Mutagenesis studies showed that RT RNase H domain residues Asn474 and Tyr501, and in a lesser extent Ala502 and Ala508, are critical for RMNC6 inhibition of the endonuclease activity of the RT, without affecting its DNA polymerization activity. Our results show that RMNC6 acts as a dual inhibitor with allosteric sites in the DNA polymerase and the RNase H domains of HIV-1 R
Violation of Bell's Inequality with Photons from Independent Sources
We report a violation of Bell's inequality using one photon from a parametric
down-conversion source and a second photon from an attenuated laser beam. The
two photons were entangled at a beam splitter using the post-selection
technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]. A quantum
interference pattern with a visibility of 91% was obtained using the photons
from these independent sources, as compared with a visibility of 99.4% using
two photons from a central parametric down-conversion source.Comment: 4 pages, 5 figures; minor change
Generating Entangled Two-Photon States with Coincident Frequencies
It is shown that parametric downconversion, with a short-duration pump pulse
and a long nonlinear crystal that is appropriately phase matched, can produce a
frequency-entangled biphoton state whose individual photons are coincident in
frequency. Quantum interference experiments which distinguish this state from
the familiar time-coincident biphoton state are described.Comment: Revised version (a typo was corrected) as published on PR
A cis-Acting Element in Retroviral Genomic RNA Links Gag-Pol Ribosomal Frameshifting to Selective Viral RNA Encapsidation
SummaryDuring retroviral RNA encapsidation, two full-length genomic (g) RNAs are selectively incorporated into assembling virions. Packaging involves a cis-acting packaging element (Κ) within the 5âČ untranslated region of unspliced HIV-1 RNA genome. However, the mechanism(s) that selects and limits gRNAs for packaging remains uncertain. Using a dual complementation system involving bipartite HIV-1 gRNA, we observed that gRNA packaging is additionally dependent on a cis-acting RNA element, the genomic RNA packaging enhancer (GRPE), found within the gag p1-p6 domain and overlapping the Gag-Pol ribosomal frameshift signal. Deleting or disrupting the two conserved GRPE stem loops diminished gRNA packaging and infectivity >50-fold, while deleting gag sequences between Κ and GRPE had no effect. Downregulating the translation termination factor eRF1 produces defective virus particles containing 20 times more gRNA. Thus, only the HIV-1 RNAs employed for Gag-Pol translation may be specifically selected for encapsidation, possibly explaining the limitation of two gRNAs per virion
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