Generation of maximally entangled states of qudits using twin photons

We report an experiment to generate maximally entangled states of D-dimensional quantum systems, qudits, by using transverse spatial correlations of two parametric down-converted photons. Apertures with D-slits in the arms of the twin fotons define the qudit space. By manipulating the pump beam correctly the twin photons will pass only by symmetrically opposite slits, generating entangled states between these differents paths. Experimental results for qudits with D=4 and D=8 are shown. We demonstrate that the generated states are entangled states.Comment: 04 pages, 04 figure

Quark mixings as a test of a new symmetry of quark Yukawa couplings

Based on the hierarchy exhibited by quarks masses at low energies, we assume that Yukawa couplings of up and down quarks are related by $Y_u\propto Y_d^2$ at grand unification scales. This ansatz gives rise to a symmetrical CKM matrix at the grand unification (GU) scale. Using three specific models as illustrative examples for the evolution down to low energies, we obtain the entries and asymmetries of the CKM matrix which are in very good agreement with their measured values. This indicates that the small asymmetry of the CKM matrix at low energies may be the effect of the renormalization group evolution only.Comment: LaTeX file, 10 pages including 1 tabl

Many families of Caenorhabditis elegans microRNAs are not essential for development or viability

available in PMC 2010 August 23MicroRNAs (miRNAs) are approximately 23 nt regulatory RNAs that posttranscriptionally inhibit the functions of protein-coding mRNAs. We previously found that most C. elegans miRNAs are individually not essential for development or viability and proposed that paralogous miRNAs might often function redundantly . To test this hypothesis, we generated mutant C. elegans strains that each lack multiple or all members of one of 15 miRNA families. Mutants for 12 of these families did not display strong synthetic abnormalities, suggesting that these miRNA families have subtle roles during development. By contrast, mutants deleted for all members of the mir-35 or mir-51 families died as embryos or early larvae, and mutants deleted for four members of the mir-58 family showed defects in locomotion, body size, and egg laying and an inability to form dauer larvae. Our findings indicate that the regulatory functions of most individual miRNAs and most individual families of miRNAs related in sequence are not critical for development or viability. Conversely, because in some cases miRNA family members act redundantly, our findings emphasize the importance of determining miRNA function in the absence of miRNAs related in sequence.Ellison Medical FoundationHoward Hughes Medical Institut

Trion ground state, excited states and absorption spectrum using electron-exciton basis

We solve the Schr\"{o}dinger equation for two electrons plus one hole by writing it in the electron-exciton basis. The main advantage of this basis is to eliminate the exciton contribution from the trion energy in a natural way. The interacting electron-exciton system is treated using the recently developed composite boson many-body formalism which allows an exact handling of electron exchange. We numerically solve the resulting electron-exciton Schr\"{o}dinger equation, with the exciton levels restricted to the lowest $1s, 2s$ and $3s$ states, and we derive the trion ground state energy as a function of the electron-to-hole mass ratio. While our results are in reasonable agreement with those obtained through the best variational methods using free carrier basis, this electron-exciton basis is mostly suitable to easily reach the bound and unbound trion excited states. Through their wave functions, we here calculate the optical absorption spectrum in the presence of hot carriers for 2D quantum wells. We find large peaks located at the exciton levels, which are attributed to electron-exciton (unbound) scattering states, and small peaks identified with trion bound states.Comment: 16 pages; 15 figure

Machine characterization and benchmark performance prediction

From runs of standard benchmarks or benchmark suites, it is not possible to characterize the machine nor to predict the run time of other benchmarks which have not been run. A new approach to benchmarking and machine characterization is reported. The creation and use of a machine analyzer is described, which measures the performance of a given machine on FORTRAN source language constructs. The machine analyzer yields a set of parameters which characterize the machine and spotlight its strong and weak points. Also described is a program analyzer, which analyzes FORTRAN programs and determines the frequency of execution of each of the same set of source language operations. It is then shown that by combining a machine characterization and a program characterization, we are able to predict with good accuracy the run time of a given benchmark on a given machine. Characterizations are provided for the Cray-X-MP/48, Cyber 205, IBM 3090/200, Amdahl 5840, Convex C-1, VAX 8600, VAX 11/785, VAX 11/780, SUN 3/50, and IBM RT-PC/125, and for the following benchmark programs or suites: Los Alamos (BMK8A1), Baskett, Linpack, Livermore Loops, Madelbrot Set, NAS Kernels, Shell Sort, Smith, Whetstone and Sieve of Erathostenes

Two minor determinants of myelin basic protein induce experimental allergic encephalomyelitis in SJL/J mice

Experimental allergic encephalomyelitis (EAE)' is an autoimmune inflammatory demyelinating disease in the central nervous system (CNS) of animals immunized with myelin basic protein (MBP). The disease is directly mediated by Thelper cells that recognize MBP in the context ofclass II antigens of the MHC (1-3). In nude mice, a single clone of adoptively transferred MBP-reactive T helper cells can cause EAE (4), suggesting that these are the only T cells required for disease induction. As a prototypic model of T helper cell-mediated autoimmune disease, observations in EAE could likely be applicable to other T helper cell-mediated diseases such as murine lupus (5), thyroiditis (6), collagen arthritis (7), and adjuvant arthritis (8), as well as human autoimmune diseases. The MBP epitope is determined in part by the MHC. Using proteolytic peptide fragments of MBP, SJL/J (H-2s) and BIO.T(6R) (H-2q) mice were found to develop EAE to the COOH-terminal peptide of MBP, whereas PL/J (H-2u) and A/J (H-2k) mice developed EAE to the NH2-terminal peptide of MBP (9). Recently, by using synthetic peptides that overcome the difficulties of obtaining pure uncontaminated proteolytic peptides, a single T cell encephalitogenic epitope for PL/J mice has been identified . This epitope consists of the first nine NH2-terminal amino acid residues of MBP which must be acetylated at the a amino group to induce disease (10). Similar fine mapping of the encephalitogenic T cell epitope(s) for SJL/J mice has not been done, in part because of the large size of the COOH-terminal peptic fragment of MBP (residues 89-169 of rat MBP, reference 9). MouseMBP consists offour major forms due to differential RNA splicing of exons II and VI (11), resulting in molecular masses of 21, 18.5, 17.5, and 14 kD, in the relative amounts of 1 :10:3.5:35 . Since EAE can also be induced with the small form of rat MBP (14 kD), which has exons II and VI of the MBP gene deleted (12), the COOH-terminal encephalitogenic determinant for SJL/J mice must be present within a segment ofonly 42 amino acid residues . Consistent withthis notion is the observation that this peptide sequence is identical among the MBPs of several mammalian species, including mouse, rat, bovine, guinea pig, and porcine, all of which can induce EAE in SJL/mice (13, 14). To identify the SJL/J encephalitogenic T cell epitope(s), overlapping peptides to the COOH-terminal region ofthe small form of mouse MBP were synthesized. Two overlapping peptides encompassing an 18-amino acid region were found to elicit EAE in SJL/J mice. The finding of a single peptide region of MBP that is responsible for encephalitogenic T cell epitopes in SJL/J mice is analogous to that of the PL/J mice and has implications for the development of specific therapy for T cell-mediated autoimmune diseases

Recent studies of top quark properties and decays at hadron colliders

The top quark is the heaviest known elementary particle. Observed for the first time in 1995 at the Tevatron by the CDF and D0 experiments, it has become object of several studies aimed at fully characterize its properties and decays. Precise determinations of top quark characteristics verify the internal consistency of the standard model and are sensitive to new physics phenomena. With the advent of the large top quark production rates generated at the LHC, top quark studies have reached unprecedented statistical precision. This review summarizes the recent measurements of top quark properties and studies of its decays performed at the LHC and Tevatron.Comment: 13 pages, 4 figures, 5 tables, Presented at Flavor Physics and CP Violation (FPCP 2012), Hefei, China, May 21-25, 201

Scalar FCNC and rare top decays in a two Higgs doublet model "for the top"

In the so called two Higgs doublet model for the top-quark (T2HDM), first suggested by Das and Kao, the top quark receives a special status, which endows it with a naturally large mass, and also potentially gives rise to large flavor changing neutral currents (FCNC) only in the up-quark sector. In this paper we calculate the branching ratio (BR) for the rare decays t->ch and h->tc (h is a neutral Higgs) in the T2HDM, at tree level and at 1-loop when it exceeds the tree-level. We compare our results to predictions from other versions of 2HDM's and find that the scalar FCNC in the T2HDM can play a significant role in these decays. In particular, the 1-loop mediated decays can be significantly enhanced in the T2HDM compared to the 2HDM of types I and II, in some instances reaching BR~10^-4 which is within the detectable level at the LHC.Comment: added two references. 15 pages, 14 figure