46,344 research outputs found
GHZ-type and W-type entangled coherent states: generation and Bell-type inequality tests without photon counting
We study GHZ-type and W-type three-mode entangled coherent states. Both the
types of entangled coherent states violate Mermin's version of the Bell
inequality with threshold photon detection (i.e., without photon counting).
Such an experiment can be performed using linear optics elements and threshold
detectors with significant Bell violations for GHZ-type entangled coherent
states. However, to demonstrate Bell-type inequality violations for W-type
entangled coherent states, additional nonlinear interactions are needed. We
also propose an optical scheme to generate W-type entangled coherent states in
free-traveling optical fields. The required resources for the generation are a
single-photon source, a coherent state source, beam splitters, phase shifters,
photodetectors, and Kerr nonlinearities. Our scheme does not necessarily
require strong Kerr nonlinear interactions, i.e., weak nonlinearities can be
used for the generation of the W-type entangled coherent states. Furthermore,
it is also robust against inefficiencies of the single-photon source and the
photon detectors.Comment: 8 pages, 5 figures, to be published in Phys. Rev.
Sumoylation silences the plasma membrane leak K+ channel K2P1.
Reversible, covalent modification with small ubiquitin-related modifier proteins (SUMOs) is known to mediate nuclear import/export and activity of transcription factors. Here, the SUMO pathway is shown to operate at the plasma membrane to control ion channel function. SUMO-conjugating enzyme is seen to be resident in plasma membrane, to assemble with K2P1, and to modify K2P1 lysine 274. K2P1 had not previously shown function despite mRNA expression in heart, brain, and kidney and sequence features like other two-P loop K+ leak (K2P) pores that control activity of excitable cells. Removal of the peptide adduct by SUMO protease reveals K2P1 to be a K+-selective, pH-sensitive, openly rectifying channel regulated by reversible peptide linkage
Recombinant Collagen Engineered to Bind to Discoidin Domain Receptors Functions as a Receptor Inhibitor
A bacterial collagen-like protein Scl2 has been developed as a recombinant collagen model system to host human collagen ligand-binding sequences, with the goal of generating biomaterials with selective collagen bioactivities. Defined binding sites in human collagen for integrins, fibronectin, heparin, and MMP-1 have been introduced into the triple-helical domain of the bacterial collagen and led to the expected biological activities. The modular insertion of activities is extended here to the discoidin domain receptors (DDRs), which are collagen-activated receptor tyrosine kinases. Insertion of the DDR-binding sequence from human collagen III into bacterial collagen led to specific receptor binding. However, even at the highest testable concentrations, the construct was unable to stimulate DDR autophosphorylation. The recombinant collagen expressed in Escherichia coli does not contain hydroxyproline (Hyp), and complementary synthetic peptide studies showed that replacement of Hyp by Pro at the critical Gly-Val-Met-Gly-Phe-Hyp position decreased the DDR-binding affinity and consequently required a higher concentration for the induction of receptor activation. The ability of the recombinant bacterial collagen to bind the DDRs without inducing kinase activation suggested it could interfere with the interactions between animal collagen and the DDRs, and such an inhibitory role was confirmed in vitro and with a cell migration assay. This study illustrates that recombinant collagen can complement synthetic peptides in investigating structure-activity relationships, and this system has the potential for the introduction or inhibition of specific biological activities
Two-photon absorption in potassium niobate
We report measurements of thermal self-locking of a Fabry-Perot cavity
containing a potassium niobate (KNbO3) crystal. We develop a method to
determine linear and nonlinear optical absorption coefficients in intracavity
crystals by detailed analysis of the transmission lineshapes. These lineshapes
are typical of optical bistability in thermally loaded cavities. For our
crystal, we determine the one-photon absorption coefficient at 846 nm to be
(0.0034 \pm 0.0022) per m and the two-photon absorption coefficient at 846 nm
to be (3.2 \pm 0.5) \times 10^{-11} m/W and the one-photon absorption
coefficient at 423 nm to be (13 \pm 2) per m. We also address the issue of
blue-light-induced-infrared-absorption (BLIIRA), and determine a coefficient
for this excited state absorption process. Our method is particularly well
suited to bulk absorption measurements where absorption is small compared to
scattering. We also report new measurements of the temperature dependence of
the index of refraction at 846 nm, and compare to values in the literature.Comment: 8 pages. To appear in J. Opt. Soc. Am.
Microlensing Characterization of Wide-Separation Planets
With their excellent photometric precision and dramatic increase in
monitoring frequency, future microlensing survey experiments are expected to be
sensitive to very short time-scale, isolated events caused by free-floating and
wide-separation planets with mass as low as a few lunar masses. We estimate the
probability of measuring the Einstein radius \theta_E for bound and
free-floating planets. We carry out detailed simulations of the planetary
events expected in next-generation surveys and estimate the resulting
uncertainty in \theta_E for these events. We show that, for main-sequence
sources and Jupiter-mass planets, the caustic structure of wide-separation
planets with projected separations of < 20 AU substantially increases the
probability of measuring the dimensionless source size and thus determining
\theta_E compared to the case of unbound planets. In this limit where the
source is much smaller than the caustic, the effective cross-section to measure
\theta_E to 10% is ~25% larger than the full width of the caustic. Measurement
of the lens parallax is possible for low-mass planetary events by combined
observations from the ground and a satellite located in an L2 orbit; this would
complete the mass measurements for such wide-separation planets. Finally,
short-duration events caused by bound planets can be routinely distinguished
from those caused by free-floating planets for planet-star separations < 20 AU
from either the deviations due to the planetary caustic or (more often) the
low-amplitude bump from the magnification due to the parent star.Comment: 10 pages including 7 figures. ApJ, in pres
Phonon arithmetic in a trapped ion system
Single-quantum level operations are important tools to manipulate a quantum state. Annihilation or creation of single particles translates a quantum state to another by adding or subtracting a particle, depending on how many are already in the given state. The operations are probabilistic and the success rate has yet been low in their experimental realization. Here we experimentally demonstrate (near) deterministic addition and subtraction of a bosonic particle, in particular a phonon of ionic motion in a harmonic potential. We realize the operations by coupling phonons to an auxiliary two-level system and applying transitionless adiabatic passage. We show handy repetition of the operations on various initial states and demonstrate by the reconstruction of the density matrices that the operations preserve coherences. We observe the transformation of a classical state to a highly non-classical one and a Gaussian state to a non-Gaussian one by applying a sequence of operations deterministically
Neutron and proton drip lines using the modified Bethe-Weizsacker mass formula
Proton and neutron separation energies have been calculated using the
extended Bethe-Weizsacker mass formula. This modified Bethe-Weizsacker mass
formula describes minutely the positions of all the old and the new magic
numbers. It accounts for the disappearance of some traditional magic numbers
for neutrons and provides extra stability for some new neutron numbers. The
neutron and proton drip lines have been predicted using this extended
Bethe-Weizsacker mass formula. The implications of the proton drip line on the
astrophysical rp-process and of the neutron drip line on the astrophysical
r-process have been discussed.Comment: 5 pages, 2 figure
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