969 research outputs found
Use of ERTS-1 data in the educational and applied research programs of agricultural extension
There are no author-identified significant results in this report
Practical quantum repeaters with linear optics and double-photon guns
We show how to create practical, efficient, quantum repeaters, employing
double-photon guns, for long-distance optical quantum communication. The guns
create polarization-entangled photon pairs on demand. One such source might be
a semiconducter quantum dot, which has the distinct advantage over parametric
down-conversion that the probability of creating a photon pair is close to one,
while the probability of creating multiple pairs vanishes. The swapping and
purifying components are implemented by polarizing beam splitters and
probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe
Ranking ligand affinity for the DNA minor groove by experiment and simulation
The structural and thermodynamic basis for the strength and selectivity of the interactions of minor-groove binders (MGBs) with DNA is not fully understood. In 2003 we reported the first example of a thiazole containing MGB that bound in a phase shifted pattern that spanned 6 base-pairs rather than the usual 4 (for tricyclic distamycin-like compounds). Since then, using DNA footprinting, nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and molecular dynamics, we have established that the flanking bases around the central 4 being read by the ligand have subtle effects on recognition. We have investigated the effect of these flanking sequences on binding and the reasons for the differences and established a computational method to rank ligand affinity against varying DNA sequences
Bright single-photon sources in bottom-up tailored nanowires
The ability to achieve near-unity light extraction efficiency is necessary
for a truly deterministic single photon source. The most promising method to
reach such high efficiencies is based on embedding single photon emitters in
tapered photonic waveguides defined by top-down etching techniques. However,
light extraction efficiencies in current top-down approaches are limited by
fabrication imperfections and etching induced defects. The efficiency is
further tempered by randomly positioned off-axis quantum emitters. Here, we
present perfectly positioned single quantum dots on the axis of a tailored
nanowire waveguide using bottom-up growth. In comparison to quantum dots in
nanowires without waveguide, we demonstrate a 24-fold enhancement in the single
photon flux, corresponding to a light extraction efficiency of 42 %. Such high
efficiencies in one-dimensional nanowires are promising to transfer quantum
information over large distances between remote stationary qubits using flying
qubits within the same nanowire p-n junction.Comment: 19 pages, 6 figure
Microwave Assisted Synthesis of Py-Im Polyamides
Microwave synthesis was utilized to rapidly build Py-Im polyamides in high yields and purity using Boc-protection chemistry on Kaiser oxime resin. A representative polyamide targeting the 5′-WGWWCW-3′ (W = A or T) subset of the consensus Androgen and Glucocorticoid Response Elements was synthesized in 56% yield after 20 linear steps and HPLC purification. It was confirmed by Mosher amide derivatization of the polyamide that a chiral α-amino acid does not racemize after several additional coupling steps
An entangled two photon source using biexciton emission of an asymmetric quantum dot in a cavity
A semiconductor based scheme has been proposed for generating entangled
photon pairs from the radiative decay of an electrically-pumped biexciton in a
quantum dot. Symmetric dots produce polarisation entanglement, but
experimentally-realised asymmetric dots produce photons entangled in both
polarisation and frequency. In this work, we investigate the possibility of
erasing the `which-path' information contained in the frequencies of the
photons produced by asymmetric quantum dots to recover polarisation-entangled
photons. We consider a biexciton with non-degenerate intermediate excitonic
states in a leaky optical cavity with pairs of degenerate cavity modes close to
the non-degenerate exciton transition frequencies. An open quantum system
approach is used to compute the polarisation entanglement of the two-photon
state after it escapes from the cavity, measured by the visibility of
two-photon interference fringes. We explicitly relate the two-photon visibility
to the degree of Bell-inequality violation, deriving a threshold at which
Bell-inequality violations will be observed. Our results show that an ideal
cavity will produce maximally polarisation-entangled photon pairs, and even a
non-ideal cavity will produce partially entangled photon pairs capable of
violating a Bell-inequality.Comment: 16 pages, 10 figures, submitted to PR
Polarization-Correlated Photon Pairs from a Single Quantum Dot
Polarization correlation in a linear basis, but not entanglement, is observed
between the biexciton and single-exciton photons emitted by a single InAs
quantum dot in a two-photon cascade. The results are well described
quantitatively by a probabilistic model that includes two decay paths for a
biexciton through a non-degenerate pair of one-exciton states, with the
polarization of the emitted photons depending on the decay path. The results
show that spin non-degeneracy due to quantum-dot asymmetry is a significant
obstacle to the realization of an entangled-photon generation device.Comment: 4 pages, 4 figures, revised discussio
Expanding the Repertoire of Natural Product-Inspired Ring Pairs for Molecular Recognition of DNA
A furan amino acid, inspired by the recently discovered proximicin natural products, was incorporated into the scaffold of a DNA-binding hairpin polyamide. While unpaired oligomers of 2,4-disubstituted furan amino acids show poor DNA-binding activity, furan (Fn) carboxamides paired with N-methylpyrrole (Py) and N-methylimidazole (Im) rings demonstrate excellent stabilization of duplex DNA as well as discrimination of noncognate sequences, consistent with function as a Py mimic according to the Py/Im polyamide pairing rules
Improving the performance of bright quantum dot single photon sources using amplitude modulation
Single epitaxially-grown semiconductor quantum dots have great potential as
single photon sources for photonic quantum technologies, though in practice
devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude
modulation can improve the performance of quantum-dot-based sources. Starting
with a bright source consisting of a single quantum dot in a fiber-coupled
microdisk cavity, we use synchronized amplitude modulation to temporally filter
the emitted light. We observe that the single photon purity, temporal overlap
between successive emission events, and indistinguishability can be greatly
improved with this technique. As this method can be applied to any triggered
single photon source, independent of geometry and after device fabrication, it
is a flexible approach to improve the performance of solid-state systems, which
often suffer from excess dephasing and multi-photon background emission
A semiconductor source of triggered entangled photon pairs?
The realisation of a triggered entangled photon source will be of great
importance in quantum information, including for quantum key distribution and
quantum computation. We show here that: 1) the source reported in ``A
semiconductor source of triggered entangled photon pairs''[1. Stevenson et al.,
Nature 439, 179 (2006)]} is not entangled; 2) the entanglement indicators used
in Ref. 1 are inappropriate, relying on assumptions invalidated by their own
data; and 3) even after simulating subtraction of the significant quantity of
background noise, their source has insignificant entanglement.Comment: 5 pages in pre-print format, 1 tabl
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