913 research outputs found
Heralded generation of entangled photon pairs
Entangled photons are a crucial resource for quantum communication and linear
optical quantum computation. Unfortunately, the applicability of many
photon-based schemes is limited due to the stochastic character of the photon
sources. Therefore, a worldwide effort has focused in overcoming the limitation
of probabilistic emission by generating two-photon entangled states conditioned
on the detection of auxiliary photons. Here we present the first heralded
generation of photon states that are maximally entangled in polarization with
linear optics and standard photon detection from spontaneous parametric
down-conversion. We utilize the down-conversion state corresponding to the
generation of three photon pairs, where the coincident detection of four
auxiliary photons unambiguously heralds the successful preparation of the
entangled state. This controlled generation of entangled photon states is a
significant step towards the applicability of a linear optics quantum network,
in particular for entanglement swapping, quantum teleportation, quantum
cryptography and scalable approaches towards photonics-based quantum computing
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
Spectroscopy by frequency entangled photon pairs
Quantum spectroscopy was performed using the frequency-entangled broadband
photon pairs generated by spontaneous parametric down-conversion. An absorptive
sample was placed in front of the idler photon detector, and the frequency of
signal photons was resolved by a diffraction grating. The absorption spectrum
of the sample was measured by counting the coincidences, and the result is in
agreement with the one measured by a conventional spectrophotometer with a
classical light source.Comment: 11 pages, 5 figures, to be published in Phys. Lett.
Monomiality principle, Sheffer-type polynomials and the normal ordering problem
We solve the boson normal ordering problem for
with arbitrary functions and and integer , where and
are boson annihilation and creation operators, satisfying
. This consequently provides the solution for the exponential
generalizing the shift operator. In the
course of these considerations we define and explore the monomiality principle
and find its representations. We exploit the properties of Sheffer-type
polynomials which constitute the inherent structure of this problem. In the end
we give some examples illustrating the utility of the method and point out the
relation to combinatorial structures.Comment: Presented at the 8'th International School of Theoretical Physics
"Symmetry and Structural Properties of Condensed Matter " (SSPCM 2005),
Myczkowce, Poland. 13 pages, 31 reference
On EPR paradox, Bell's inequalities and experiments which prove nothing
This article shows that the there is no paradox. Violation of Bell's
inequalities should not be identified with a proof of non locality in quantum
mechanics. A number of past experiments is reviewed, and it is concluded that
the experimental results should be re-evaluated. The results of the experiments
with atomic cascade are shown not to contradict the local realism. The article
points out flaws in the experiments with down-converted photons. The
experiments with neutron interferometer on measuring the "contextuality" and
Bell-like inequalities are analyzed, and it is shown that the experimental
results can be explained without such notions. Alternative experiment is
proposed to prove the validity of local realism.Comment: 27 pages, 8 figures. I edited a little the text and abstract I
corrected equations (49) and (50
JWST Detects Neon Line Variability in a Protoplanetary Disk
We report the first detection of variability in the mid-infrared neon line
emission of a protoplanetary disk by comparing a JWST MIRI MRS spectrum of SZ
Cha taken in 2023 with a Spitzer IRS SH spectrum of this object from 2008. We
measure the [Ne III]-to-[Ne II] line flux ratio, which is a diagnostic of the
high-energy radiation field, to distinguish between the dominance of EUV- or
X-ray-driven disk photoevaporation. We find that the [Ne III]-to-[Ne II] line
flux ratio changes significantly from in 2008 to in 2023.
This points to a switch from EUV-dominated to X-ray-dominated photoevaporation
of the disk. We present contemporaneous ground-based optical spectra of the
Halpha emission line that show the presence of a strong wind in 2023. We
propose that this strong wind prevents EUV radiation from reaching the disk
surface while the X-rays permeate the wind and irradiate the disk. We speculate
that at the time of the Spitzer observations, the wind was suppressed and EUV
radiation reached the disk. These observations confirm that the MIR neon
emission lines are sensitive to changes in high-energy radiation reaching the
disk surface. This highlights the [Ne III]-to-[Ne II] line flux ratio as a tool
to gauge the efficiency of disk photoevaporation in order to provide
constraints on the planet-formation timescale. However, multiwavelength
observations are crucial to interpret the observations and properly consider
the star-disk connection.Comment: Accepted to ApJ
Tight Finite-Key Analysis for Quantum Cryptography
Despite enormous progress both in theoretical and experimental quantum
cryptography, the security of most current implementations of quantum key
distribution is still not established rigorously. One of the main problems is
that the security of the final key is highly dependent on the number, M, of
signals exchanged between the legitimate parties. While, in any practical
implementation, M is limited by the available resources, existing security
proofs are often only valid asymptotically for unrealistically large values of
M. Here, we demonstrate that this gap between theory and practice can be
overcome using a recently developed proof technique based on the uncertainty
relation for smooth entropies. Specifically, we consider a family of
Bennett-Brassard 1984 quantum key distribution protocols and show that security
against general attacks can be guaranteed already for moderate values of M.Comment: 11 pages, 2 figure
Stochasticity of flow through microcirculation as a regulator of oxygen delivery
<p>Abstract</p> <p>Objective</p> <p>Observations of microcirculation reveal that the blood flow is subject to interruptions and resumptions. Accepting that blood randomly stops and resumes, one can show that the randomness could be a powerful means to match oxygen delivery with oxygen demand.</p> <p>Method</p> <p>The ability of the randomness to regulate oxygen delivery is based on two suppositions: (a) the probability for flow to stop does not depend on the time of uninterrupted flow, thus the number of interruptions of flow follows a Poisson distribution; (b) the probability to resume the flow does not depend on the time for flow being interrupted; meaning that time spent by erythrocytes at rest follows an exponential distribution. Thus the distribution of the time to pass an organ is a compound Poisson distribution. The Laplace transform of the given distribution gives the fraction of oxygen that passes the organ.</p> <p>Result</p> <p>Oxygen delivery to the tissues directly depends on characteristics of the irregularity of the flow through microcirculation.</p> <p>Conclusion</p> <p>By variation of vasomotion activity it is possible to change delivery of oxygen to a tissue by up to 8 times.</p
Mutations in the autoregulatory domain of β-tubulin 4a cause hereditary dystonia.
Dystonia type 4 (DYT4) was first described in a large family from Heacham in Norfolk with an autosomal dominantly inherited whispering dysphonia, generalized dystonia, and a characteristic hobby horse ataxic gait. We carried out a genetic linkage analysis in the extended DYT4 family that spanned 7 generations from England and Australia, revealing a single LOD score peak of 6.33 on chromosome 19p13.12-13. Exome sequencing in 2 cousins identified a single cosegregating mutation (p.R2G) in the β-tubulin 4a (TUBB4a) gene that was absent in a large number of controls. The mutation is highly conserved in the β-tubulin autoregulatory MREI (methionine-arginine-glutamic acid-isoleucine) domain, highly expressed in the central nervous system, and extensive in vitro work has previously demonstrated that substitutions at residue 2, specifically R2G, disrupt the autoregulatory capability of the wild-type β-tubulin peptide, affirming the role of the cytoskeleton in dystonia pathogenesis
Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
International audienceRecent in situ measurements at tropical tropopause temperatures as low as 187 K indicate supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of aqueous aerosol freezing. The high supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values are at least 20% too low, (2) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing, and (3) if surface freezing dominates, organic coatings may increase the surface energy of the ice embryo/vapor interface resulting in suppressed ice nucleation. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere. The TTL cirrus simulations show that even if very large supersaturations are required for ice nucleation, these large supersaturations should occur very rarely
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