bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemoenzymatic synthesis of thio-nod factor intermediates  Enzymatic transfer of glucosamine on thiochitobiose derivatives
Authors: Morais Latino Loureiro , Yuasa Hideya , Bennis Khalil , Ripoche Isabelle , Auzanneau France-Isabelle
Published: May 2006

The chemoenzymatic syntheses of thioanalogues of nodulation factors in which the nonreducing end glucosamine residue is available for the introduction of the fatty acid moiety at the free NH2group are reported. We are describing the chemical synthesis of UDP-GlcNH2and its use in the enzymatic transfer of GlcNH2by the bovine galactosyltransferase (EC 2.4.1.90) onto O-4 of the nonreducing end N-acetylglucosamine residues of chitobiose, thiochitobiose, and allyl thiochitobioside. The enzymatic reactions on chitobiose and thiochitobiose were followed by TLC and MALDI MS and showed about 50% conversion of the disaccharides to the desired products. However, these reducing trisaccharides could not be obtained totally free of salts and degraded on ion exchange chromatography. Thus, we investigated the enzymatic transfer on the nonreducing allyl thiochitobioside analogue. We describe here the chemical synthesis of this thiodisaccharide and the enzymatic transfer of GlcNH2at O-4 of its nonreducing end glucosamine residue to give the desired allyl thiotrisaccharide. This thiotrisaccharide was obtained pure in 41% yield and was characterized by1H NMR (HSQC) and HRMS.Key words: nodulation factors, synthesis, enzymatic transfer, thiooligosaccharides, UDP-glucosamine.
Stereoselective synthesis of dioxabicycles from 1-C-allyl-2-O-benzyl-glycosides  An intramolecular cyclization between 2-O-benzyl oxygen and the allyl double bond
Authors: Wu An-Tai , Yi Tian , Shao Huawu , Wu Shih-Hsiung , Zou Wei
Published: May 2006

Addition of a proton to the double bond of 1-C-allyl-O-benzylglycosides gave a 2′-carbonium ion, which in turn reacted intramolecularly, in a regio- and diastereo-selective manner, with the nucleophilic oxygen of the 2-O-benzyl group to form an oxonium intermediate. Subsequent cleavage of the benzyl CO bond led to dioxabicycles in moderate yields. Surprisingly, opposite diastereoselectivities were observed from 1-C-allylglycofuranosides and 1-C-allylglycopyranosides, which produced 2,2′-trans- and 2,2′-cis-dioxabicycles, respectively.Key words: C-glycoside, olefin, cyclization, oxocarbonium, dioxabicycles.
Component analysis of the X-C-Y anomeric effect (X = O, S; Y = F, OMe, NHMe) by DFT molecular orbital calculations and natural bond orbital analysis
Authors: Trapp Melissa L , Watts Jonathan K , Weinberg Noham , Pinto B Mario
Published: May 2006

Six 2-Y-substituted oxacyclohexane and thiacyclohexane heterocycles (Y = F, OMe, NHMe) were examined using DFT molecular orbital calculations. Natural bond orbital (NBO) analysis of the total energy behaviour yielded the orbital-interaction factors contributing to the conformational equilibria. The dipole moments of the optimized systems were used to estimate the electrostatic contributions to the anomeric effect. The primary determinant of the X-C-Y anomeric effect was found to be the orbital interaction components associated with the combined endo- and exo-anomeric effects acting in concert in the axial conformers. Electrostatic interactions made a contribution to the observed conformer stabilization in all cases, but did not account for the relative magnitudes of the energy differences among conformers of homologous molecules. In the case of the methylamino substituent, accentuated steric interactions in the axial conformer precluded stabilization by the exo-anomeric interaction and consequently, the net endo/exo anomeric stabilization did not dominate the conformational equilibria.Key words: anomeric effect, component analysis, natural bond orbital analysis, electrostatic, steric, and orbital interaction effects.
Quantum mechanics studies of cellobiose conformations
Authors: French Alfred D , Johnson Glenn P
Published: May 2006

Three regions of the conformation space that describes the relative orientations of the two glucose residues of cellobiose were analyzed with quantum mechanics. A central region, in which most crystal structures are found, was covered by a 9 × 9 grid of 20° increments of the linkage torsion angles ϕ and ψ. Besides these 81 constrained minimizations, we studied two central subregions and two regions at the edges of our maps of complete ϕ,ψ space with unconstrained minimization, for a total of 85 target geometries. HF/6-31G(d) and single-point HF/6-311+G(d) calculations were used to find the lowest energies for each geometry. B3LYP/6-31G+G(d) and single point B3LYP/6-11+G(d) calculations were also used for all unconstrained minimizations. For each target, 181 starting geometries were tried (155 for the unconstrained targets). Numerous different starting geometries resulted in the lowest energies for the various target structures. The starting geometries came from five different sets that were based on molecular mechanics energies. Although all five sets contributed to the adiabatic map, use of any single set resulted in discrepancies of 37 kcal/mol (1 cal = 4.184 J) with the final map. For most of the targets, the starting geometry that gave the lowest energy depended on the basis set and whether the HF or B3LYP method was used. However, each of the above four calculations gave the same overall lowest energy structure that was found previously by Strati et al. This global minimum, stabilized by highly cooperative hydrogen bonds, is in a region that is essentially not populated by crystal structures. HF/6-31G(d) energy contours of the mapped central region were compatible with the observed crystal structures. Observed structures that lacked O3···O5′ hydrogen bonds were about 1 kcal/mol above the map's minimum, and observed structures that have a pseudo twofold screw axis ranged from about 0.4 to 1.0 kcal/mol. The HF/6-311+G(d) map accommodated the observed structures nearly as well.Key words: cellulose, carbohydrate, conformation, energy, flexibility, folding, helix, shape.
Enantiomeric synthesis of carbocyclic analogs ofD- andL-6-azapyrimidine ribonucleosides
Authors: Liu Peng , Chu Chung K
Published: May 2006

An effective and practical synthesis of carbocyclic D- and L-6-azapyrimidine nucleosides (38) was described. Starting from D-ribose, a new efficient methodology for the synthesis of L-2,3-O-cyclohexylidene-4-cyclopentenone (23) was developed via a ring-closing metathesis, which was applied for the synthesis of L-cyclopentyl-6-azapyrimidine nucleosides (68). The regiospecific introduction of 6-azauracil on the carbocyclic moiety (9 and 25) was also achieved by masking its N3position with a 4-methylthio group.Key words: carbocyclic nucleosides, 6-azapyrimidine nucleosides, enantiomeric synthesis.
Complexation of diazinon, an organophosphorus pesticide, with α-, β-, and γ-cyclodextrin  NMR and computational studies
Authors: Churchill Doreen , Cheung Jason Chiu Fung , Park Yong Sung , Smith Vedene H , vanLoon Gary , Buncel Erwin
Published: May 2006

Complexation of the organophosphorus pesticide, diazinon, with α-, β- and γ- cyclodextrin has been investigated through NMR and computational methodologies. Binding constants (Kb) determined by 1H and 31P NMR follow the order γ-CD > α-CD = β-CD, in contrast with reported Kb data for other pesticides and thus indicative of steric encumbrance by the isopropyl group in diazinon being an important factor influencing binding constants. The interaction of diazinon with the CDs has also been investigated through computational studies via molecular dynamics  molecular mechanics (MDMM2) and density functional theory (DFT), B3LYP/6-31G*. It is shown that the most favorable orientation in binding corresponds to the hydrophobic heterocyclic residue of diazinon being pulled deepest into the CD cavity, in agreement with the experimentally determined order of binding constants. Moreover, the computations show that it is only with γ-CD that the heterocyclic residue of diazinon and the phosphoryl residue are both largely encrypted in the CD cavity, marking a clear differentiation with α-CD and β-CD where the phosphoryl residue is located largely outside the cavity. Thus, the computational results are in essential agreement with the experimental binding constants where γ-CD stands out with the highest Kb value. Our work could point to the potential usefulness of computational studies to be undertaken in tandem with experimental work in environmental situations such as soil remediation.Key words: organophosphorus pesticides, diazinon complexation, cyclodextrins, computational studies, molecular mechanics.
From enolates to anthraquinones
Authors: Bailey David , Murphy Jeffrey N , Williams Vance E
Published: May 2006

A series of highly reactive cyclopentadienones were prepared in situ from the corresponding hydroxycyclopent-2-enones and trapped with a variety of quinones. Reaction of 1,4-naphthoquinone with 4-hydroxy-3,4-diphenyl-cyclopent-2-enone afforded 2,3-diphenylanthraquinone, whereas reaction of benzoquinone with this same cyclopentadienone precursor yielded a mixture of 6,7-diphenyl-1,4-naphthoquinone and 2,3,6,7-tetraphenyl anthraquinone. A number of other 2,3-diarylanthraquinones were likewise prepared in moderate yields from the reaction of 1,4-naphthoquinone with the appropriate 4-hydroxy-3,4-diarylcyclopent-2-enones. This method appears to be generally applicable to the synthesis of anthraquinone derivatives substituted at the 2- and 3-positions from inexpensive starting materials.Key words: anthraquinone, DielsAlder, cyclopentadienone, in situ.
Conformational analysis in aqueous solution and estimation of the persistence length of exopolysaccharides produced byLactobacillus helveticusLh59 andStreptococcus macedonicusSc136
Authors: Kuik J Albert van , Vincent Sébastien JF , Leeflang Bas R , Kroon-Batenburg Loes MJ , Kamerling Johannis P
Published: May 2006

The conformations of two exopolysaccharides, one produced by Lactobacillus helveticus Lh59 and one by Streptococcus macedonicus Sc136, were investigated by molecular modelling to get insight into their physical properties. In particular, the influence of side chains and glycosidic linkage types on the overall shapes and persistence lengths of the polysaccharides were studied. It appeared that the side chains had only minor effects on the persistence lengths of the polysaccharides, with the exception of the monosaccharide residue directly attached to the backbone. The extensiveness of the backbone is enhanced by β-D-Hexp-(1→4) structural elements, whereas α-D-Hexp-(1→3) and α-D-Hexp-(1→4) elements create structural variability by introducing bends. The occurrence of either (1→5)- or (1→6)-linked monosaccharides, resulting in one extra bond between monosaccharide units, causes the overall flexibility of the polysaccharide chain to be enhanced and extensiveness to be reduced. The presence of such flexible linkages in the backbone leads to a shorter persistence length than when present in the side chain: a value of only 4.5 nm was found for the L. helveticus Lh59 EPS with a (1→5) linkage in the backbone, and a value of 8.5 nm for the S. macedonicus Sc136 EPS with two (1→6) linkages in the side chain.Key words: conformational analysis, exopolysaccharide, Lactobacillus helveticus, molecular modelling, persistence length, Streptococcus macedonicus.
Photochemical reactions of thiols with organic nitrates  Oxygen atom transfer via a thionitrate
Authors: Clarke Jennifer L , Kastrati Irida , Johnston Linda J , Thatcher Gregory RJ
Published: May 2006

Nitroglycerin is an organic nitrate that has been used in the clinical treatment of angina for 130 years, yet important details of its mechanism of action remain unanswered. The biological activity of nitrates suggests that they are bioactivated to NO via a three-electron reduction. The involvement of free or bound protein thiols in this reduction has often been proposed. To examine the involvement of thiyl radicals in such a process, the photochemical generation of benzenethiyl radical from thiol and disulfide precursors was studied in the presence of isopropyl nitrate. Analysis of reaction products and kinetics led to the conclusion that photolysis of the nitrate to NO2dominated the observed photochemistry. Formation of sulfonothioate and NO as products, and trapping of NO2by 4-chlorophenol, indicated a mechanism involving oxygen atom transfer from N to S via a thionitrate intermediate. The results of the study did not indicate a rapid reaction between thiyl radical and organic nitrate. Despite weak nitrate absorption of light >300 nm and a relatively high BDE for homolysis to give NO2, the photochemistry under thiyl-generating conditions was driven by nitrate photolysis to NO2. A novel nitrate, containing a phenyl disulfanyl group linked to nitrate groups, did not undergo photolysis to NO2or generate sulfonothioate, but did yield NO. These observations suggest that reaction between thiyl radicals and nitrates leading to NO release is a viable pathway, but it is subservient to other competing reactions, such as photolysis, in the case of IPN, and reaction with thiolate, in the case of the novel nitrate.Key words: nitrate, photolysis, thiyl radical, nitrogen dioxide, nitric oxide.
DNA and RNA enzymes with peroxidase activity  An investigation into the mechanism of action
Authors: Travascio Paola , Sen Dipankar , Bennet Andrew J
Published: May 2006

A DNAhemin complex (PS2.Mhemin), and its RNA counterpart (rPS2.Mhemin), have previously been reported, in the presence of nitrogenous buffers such as HEPES, to show enhanced peroxidative activity relative to both uncomplexed hemin and a control DNAhemin complex (Chem. Biol. 5, 505, 1998). A kinetic analysis of these two hemin-utilizing nucleic acid enzymes provides key insights into the mechanisms for their catalyzed peroxidation reactions. First, control experiments indicate that charge on the added detergent, required for solubility reasons, has little effect on the efficiency of the nucleic-acid-catalyzed reactions. Second, the key functional impact of the two nucleic acid frameworks, either DNA or RNA, appears to be a reduction in the acidity of a water molecule coordinated to the iron atom of the hemin that is bound to the ribozyme and DNAzyme scaffolds. This effect could result from a polar environment and possibly hydrogen bond(s) at the axial position of the hemin, along with favourable hydrophobic interactions for the periphery of the porphyrin ring. Third, the basic component of the buffer enhances the activities; this likely results from a general-base-catalyzed process. Cumulatively, these data supply important clues as to how biopolymers other than a protein can complex with hemin to form productive peroxidase enzymes.Key words: ribozyme, DNAzyme, hemin, peroxidase, mechanism, guanine quadruplex.
A topological analysis of the interion interactions of tetraphenylphosphonium squarate
Authors: Wolstenholme David , Aquino Manuel AS , Cameron T Stanley , Ferrara Joseph D , Robertson Katherine N
Published: May 2006

The tetraphenylphosphonium squarate salt crystallizes with a number of diverse interactions, which all have the potential to be classified as hydrogen bonds. The squarate anions are found as dimers linked by O-H···O interactions. The multipole refinement of the tetraphenylphosphonium squarate was performed using the HansenCoppens model followed by topological analysis of its intermolecular interactions. A total of 28 interactions were found among the symmetry related molecules, which include a number of C-H···Cπ, C-H···O, and C-H···H-C interactions, along with the O-H···O interaction. With the criteria for hydrogen bonding proposed by Popelier and Koch, it is possible to determine which of these interactions are hydrogen bonds and which are van der Waals interactions. Both linear and exponentially dependent correlations can be seen for the properties of the bond critical points involving the intermolecular interactions that fulfill these criteria. All this leads to a better understanding of the role that hydrogen bonds play in the formation of small organic compounds.Key words: electron density, multiple refinement, hydrogen bonds.
Stereoselective synthesis of chiral piperidine derivatives employing arabinopyranosylamine as the carbohydrate auxiliary
Authors: Kranke Birgit , Kunz Horst
Published: May 2006

Stereoselective synthesis of 2-substituted dehydropiperidinones and their further transformation to variously disubstituted piperidine derivatives was achieved employing D-arabinopyranosylamine as the stereodifferentiating carbohydrate auxiliary. A domino MannichMichael reaction of 1-methoxy-3-(trimethylsiloxy)butadiene (Danishefsky's diene) with O-pivaloylated arbinosylaldimines furnished N-arabinosyl dehydropiperidinones in high diastereoselectivity. Subsequent conjugate cuprate addition gave 2,6-cis-substituted piperidinones, while enolate alkylation furnished 2,3-trans-substituted dehydropiperidinones. Electrophilic substitution at the enamine structure afforded 5-nitro- and 5-halogen dehydropiperidinones of which the latter were applied in palladium-catalyzed coupling reactions. The absolute configuration of the obtained products was proven by NMR and X-ray structure analysis as well as by syntheses of the alkaloids (+)-coniine and (+)-dihydropinidine.Key words: piperidine alkaloids, carbohydrate auxiliary, domino MannichMichael reaction, conjugate cuprate and hydride addition, electrophilic substitution of enamines.
A simple, highly regioselective and efficient reaction of indole with epoxides under solvent-free conditions
Authors: Azizi Najmedin , Mehrazma Shokopheh , Saidi Mohammad R
Published: May 2006

Lithium perchlorate has been found to be an inexpensive and efficient catalyst for the ring opening of epoxides by indole and N-methylindole, which provides an environmentally friendly method for the synthesis of substituted indoles. A complete regioselectivity in favor of nucleophilic attack at the benzylic carbon atom of aromatic epoxides, such as styrene oxide, is observed. However, aliphatic unsymmetrical alkene oxides undergo selective nucleophilic attack at the sterically less-hindered carbon atom. This catalyst offers several advantages, such as short reaction time, high yields, lower catalytic loading, simple experimental procedure, and easy isolation of the products, under solvent-free conditions.
Living biomembrane bitemplate route for simultaneous synthesis of different morphologies of CdSe and ZnSe nanomaterials
Authors: Li Li , Wu Qing-Sheng , Ding Ya-Ping
Published: May 2006

In this paper, CdSe (nanotubes, nanorods) and ZnSe (nanorods, nanoslats) were simultaneously synthesized through a biomineralization process through biomembrane bitemplates of mungbean sprouts at room temperature. The XRD patterns indicated that these nanocrystals were crystallized in the hexagonal structure and cubic structure with lattice constants a = 0.423 and c = 0.701 nm (CdSe) and a = 0.567 nm (ZnSe), respectively. The possible formation mechanism was investigated in the paper.Key words: CdSe, ZnSe, nanotubes, nanorods, nanoslats, living biomembrane, bitemplates.
Solvent-free and selective tosylation of alcohols and phenols with p-toluenesulfonyl chloride by heteropolyacids as highly efficient catalysts
Authors: Fazaeli Razieh , Tangestaninejad Shahram , Aliyan Hamid
Published: May 2006

Tosylation of some alcohols and phenols has been directly carried out with p-toluenesulfonyl chloride using heterodoxy acids (H3PW12O40, H3PMo12O40, AlPW12O40, and AlPMo12O40) as catalysts in the absence of solvent. We found that heteropoly acids AlPW12O40 and AlPMo12O40 were effective catalysts for the tosylation of alcohols and phenols. In the case of aliphatic alcohols, secondary alcohols undergo tosylation chemoselectively in the presence of primary hydroxyl groups. This new method consistently has the advantage of excellent yields and short reaction time.Key words: tosylation, p-TsCl, Keggin-type polyoxometalate, solvent-free reaction.
Titanium pyridyl-phosphinimide complexes  Synthesis, structure, and ethylene polymerization catalysis
Authors: Beddie Chad , Wei Pingrong , Stephan Douglas W
Published: May 2006

A series of Tipyridyl-phosphinimide complexes of the form Cp′TiX2[NPR2(2-CH2Py)] (Cp′ = Cp, Cp*, R = i-Pr, t-Bu, X = Cl, Me) have been prepared and characterized. These complexes generate ethylene polymerization catalysts upon activation with MAO or B(C6F5)3. The resulting polymers exhibit broad molecular weight distributions. The role of the pyridyl group is discussed in light of stoichiometric reactions of CpTiCl2[NPR2(2-CH2Py)] with B(C6F5)3.Key words: phosphinimide complexes, pyridyl-phosphinimides, olefin polymerization.
A LOWER BOUND OF THE FIRST DIRICHLET EIGENVALUE OF A COMPACT MANIFOLD WITH POSITIVE RICCI CURVATURE
Authors: LING JUN
Published: May 2006

We give a lower bound for the first Dirichlet eigenvalue for a compact manifold with positive Ricci curvature in terms of the lower bound of the Ricci curvature and the interior radius. The result sharpens earlier estimates.
MAXIMUM ENTANGLEMENT IN A JAYNES-CUMMINGS SYSTEM WITH STRONGLY DRIVEN ATOMS
Authors: CASAGRANDE F. , LULLI A.
Published: May 2006

We describe the entanglement of a Jaynes-Cummings system, where a two-level atom is also strongly driven by an external coherent field while it crosses a resonant cavity prepared in a coherent state. First we consider the atom-cavity field entanglement, described by the Von Neumann entropy. We find that it depends only on the interaction time and the initial atomic state. The entropy vanishes in the case of maximally polarized atom, independent of the interaction time, whereas it reaches its maximum value for atom in the upper or lower state and for long enough interaction times. Then we investigate the entanglement between two consecutive strongly driven atoms interacting with the cavity mode assumed in the vacuum state, showing that they never entangle in spite of the existence of atom-atom correlations.
QUANTUM 1/f NOISE AND QUANTUM 1/f PHASE NOISE RELATED TO THE UNCERTAINTY RELATIONS
Authors: HANDEL PETER H. , TOURNIER ADAM G.
Published: May 2006

Quantum 1/f noise is the manifestation of the coherent and conventional quantum 1/f effects (Q1/fE). The conventional Q1/fE is a fundamental quantum fluctuation of physical cross sections σ and process rates Γ, caused by the bremsstrahlung (recoil) energy and momentum losses of charged particles, when they are scattered, or accelerated in any way. The closely related coherent Q1/fE is present in any current carried by many particles. It is caused by the energy spread characterizing any coherent state of the electromagnetic field oscillators. According to the Heisenberg's uncertainty principle, because an approximation of the phase or position variable is known, exact knowledge of the energy is precluded. This energy spread results in nonstationary energy values, or fluctuations in the energy of the oscillators. To find the spectral density of these inescapable basic fluctuations, which are known to characterize any quantum state, which is not an energy eigenstate, we use an elementary physical derivation based on Schrödinger's definition of coherent states, which can be supplemented by a rigorous derivation from a well-known quantum-electrodynamical branch-point propagator. The example of a simple harmonic oscillator is also useful for illustrating the uncertainty that arises due to Q 1/f Noise. Clearly illustrating the relation between the uncertainty principle and Q 1/f noise.
QUANTUM 1/f EFFECT BASED ON QUANTUM INFORMATION THEORY
Authors: GEORGE THOMAS F. , HANDEL PETER H.
Published: May 2006

The Quantum Information Theory Approach (QIT) explains for the first time the apparent lack of unitarity caused by the entropy increase in the Quantum 1/f Effect (Q1/fE). This allows for a deeper understanding of the quantum 1/f effect, showing no resultant entropy increase and therefore no violation of unitarity in the quantum-mechanical dynamical evolution. This new interpretation involves the von Neumann Quantum Entropy, including the negative conditional entropy concept for quantum entangled states introduced by QIT. The Q1/fE was applied to many high-tech systems, in particular to ultra small electronic devices in nanotechnology. The present paper explains how the additional entropy implied by the observed 1/f noise arises in spite of the entropy-conserving evolution of the system. On this basis, a derivation of the conventional and coherent quantum 1/f effect is given. The latter is derived from a non-relativistic form of the branch-point propagator derived by excluding the long range Coulomb interaction from the interaction hamiltonian. The paper concludes with examples of practical applications in various devices and systems, allowing for a new characterization of high technology.
ALL-FIBRE SOURCE OF CONTINUOUS VARIABLE ENTANGLED LIGHT
Authors: NANDAN A. , SABUNCU M. , HEERSINK J. , GLÖCKL O. , LEUCHS G. , ANDERSEN U. L.
Published: May 2006

We experimentally demonstrate the production of continuous variable entanglement of femto second laser pulses from an all-fibre asymmetric Sagnac interferometer exploiting the Kerr effect. Contrary to the experiment of Silberhorn et al. [Phys. Rev. Lett. 86, 4267 (2001)], the asymmetric coupler in the Sagnac loop is fully integrated in the fibre, making the source extremely compact, reliable and robust. Employing a simple detection scheme, comprising a beam splitter and two intensity detectors, we clearly observe quantum correlations of conjugate quadratures, hereby witnessing entanglement.
CLASSIFICATION AND QUANTIFICATION OF ENTANGLED BIPARTITE QUTRIT PURE STATES
Authors: PAN FENG , LU GUOYING , DRAAYER J. P.
Published: May 2006

A complete analysis of entangled bipartite qutrit pure states is carried out based on a simple entanglement measure. An analysis of all possible extremally entangled pure bipartite qutrit states is shown to reduce, with the help of SLOCC transformations, to three distinct types. The analysis and the results should be helpful for finding different entanglement types in multipartite pure state systems.
QUANTUM LIMIT OF MEASUREMENT AND THE PROJECTION POSTULATE
Authors: GURVITZ S. A.
Published: May 2006

We study an electrostatic qubit monitored by a point-contact detector. Projecting an entire qubit-detector wave function on the detector eigenstates we determine the precision limit for the qubit measurements, allowed by quantum mechanics. We found that this quantity is determined by qubit dynamics as well as decoherence, generated by the measurement. Our results show how the quantum precision limit can be improved by a proper design of a measurement procedure.
PROBABILITY REPRESENTATION OF OPTICAL SIGNALS AND NEW ENTROPY OF QUANTUM STATES
Authors: MAN'KO MARGARITA A. , MAN'KO OLGA V. , MAN'KO VLADIMIR I.
Published: May 2006

Probability distributions (tomograms) associated to classical and quantum optical signals are introduced. Nonlinear evolution equations are discussed in the probability representation. For spin states, entropy and information corresponding to spin tomograms are studied.
CONTROL OF DECOHERENCE VIA QUANTUM ZENO SUBSPACES
Authors: FACCHI PAOLO , NAKAZATO HIROMICHI , PASCAZIO SAVERIO , TASAKI SHUICHI
Published: May 2006

We discuss three control strategies, whose objective is to counter the effects of decoherence: the first strategy hinges upon the quantum Zeno effect, the second makes use of frequent unitary interruptions ("bang-bang" pulses), and the third of a strong, continuous coupling. Decoherence can be suppressed only if the frequency τ-1 of the measurements/pulses is large enough or if the coupling K is sufficiently strong. Otherwise, if τ-1 or K are large, but not sufficiently large, all these control procedures accelerate decoherence.
GENERATION OF HIGHER ORDER NONCLASSICAL STATES VIA AN INTENSE ELECTROMAGNETIC FIELD
Authors: PATHAK ANIRBAN
Published: May 2006

Interaction of intense laser beam with an inversion symmetric third order nonlinear medium is modeled as a quartic anharmonic oscillator. A first order operator solution of the model Hamiltonian is used to study the possibilities of generation of higher order nonclassical states. It is found that the higher order squeezed and higher order antibunched states can be produced by this interaction. It is also shown that the higher order nonclassical states may appear separately, i.e. a higher order antibunched state is not essentially higher order squeezed state and vice versa.
A SCALING LAW FOR AMPLITUDE-SQUARED SQUEEZING IN KERR EFFECT
Authors: PRAKASH HARI , KUMAR PANKAJ
Published: May 2006

We study amplitude-squared squeezing in interaction of coherent light with a nonlinear Kerr medium modelled as an anharmonic oscillator with interaction Hamiltonian H = ½ λ a +2 a 2, where λ is proportional to χ(3) of the nonlinear medium and a is annihilation operator for the interacting field. We find the squeezing parameter S ( τ, r ) in terms of a dimensionless interaction time τ = λ t and Kerr parameter r , which is product of, τ and the average number of photons and obtain almost complete amplitude-squared squeezing (i.e., S ≈ 0) for very small interaction time and very large intensity of the interacting light. We optimize squeezing parameter S ( τ, r ) by an analytic estimation assuming high intensity of the interacting light and realistic values of Kerr nonlinearity following J.Bajer et al. [Czech. J. Phy. 52, 1313 (2002)] and obtain a scaling law for optimal amplitude-squared squeezing with minimum value S min , at r = r min for a given τ. The validity of the scaling law is checked numerically and analytically in the region of realistic values of Kerr nonlinearity and intensity of the interacting light.
SQUEEZING IN MULTIVARIATE SPIN SYSTEMS
Authors: SIRSI SWARNAMALA
Published: May 2006

In contrast to the canonically conjugate variates q, p representing the position and momentum of a particle in the phase space distributions, the three Cartesian components, Jx, Jy, Jz of a spin-j system constitute the mutually non-commuting variates in the quasi-probabilistic spin distributions. It can be shown that a univariate spin distribution is never squeezed and one needs to look into either bivariate or trivariate distributions for signatures of squeezing. Several such distributions result if one considers different characteristic functions or moments based on various correspondence rules. As an example, discrete probability distribution for an arbitrary spin-1 assembly is constructed using Wigner-Weyl and Margenau-Hill correspondence rules. It is also shown that a trivariate spin-1 assembly resulting from the exposure of nucleus with non-zero quadrupole moment to combined electric quadrupole field and dipole magnetic field exhibits squeezing in certain cases.
CORRELATIONS IN ENTANGLED STATES
Authors: SANCTUARY B. C.
Published: May 2006

Entangled EPR spin pairs can be treated using the statistical ensemble interpretation of quantum mechanics. As such the singlet state results from an ensemble of spin pairs each with its own specific axis of quantization. This axis acts like a quantum mechanical hidden variable. If the spins lose coherence they disentangle into a mixed state that contains classical correlations. In this paper an infinitesimal phase decoherence is introduced to the singlet state in order to reveal more clearly some of the correlations. It is shown that a singlet state has no classical correlations.
WITNESSING ENTANGLEMENT OF EPR STATES WITH SECOND-ORDER INTERFERENCE
Authors: STOBIŃSKA MAGDALENA , WÓDKIEWICZ KRZYSZTOF
Published: May 2006

The separability of the continuous-variable EPR state can be tested with Hanbury-Brown and Twiss type interference. The second-order visibility of such interference can provide an experimental test of entanglement. It is shown that time-resolved interference leads to the Hong, Ou and Mandel deep, that provides a signature of quantum non-separability for pure and mixed EPR states. A Hanbury-Brown and Twiss type witness operator can be constructed to test the quantum nature of the EPR entanglement.
THE QUANTUM ZENO EFFECT – A MATTER OF DYNAMICS, INFORMATION OR ILLUSION?
Authors: TOSCHEK PETER E.
Published: May 2006

Reiterated or continuous measurement on a quantum system impedes the quantum object's evolution. This "quantum Zeno" effect (QZE), contemplated for decades, has been conventionally attributed to the reaction of the measuring device on the quantum object being measured, in the sense of the Heisenberg microscope. However, even reactionless "quantum non-demolition" measurements seem to qualify for that inhibition to take place and may constitute a "quantum Zeno paradox" (QZP). An experimental proof of QZE had been attempted in the past on clouds of ions confined in a Paul trap. In the meantime it has been shown, however, that the anticipated impediment of the quantum evolution by a sheer gain of information, i.e. by reactionless measurement cannot be, in principle, proven with an ensemble. Recently, experiments have been performed with the use of a single quantum system: an 172Yb+ ion, laser-driven on its E2 line S1/2 - D5/2, or an 171Yb+ ion, microwave-driven on its ground-state hyperfine resonance. The results of these experiments demonstrate that mere gain of information on the quantum system, while lacking dynamic action, modifies the system's evolution as it is predicted by quantum mechanics, based on the system's preparation. This seems plausible if we attribute reality to the results of the measurements. If, in contrast, reality is claimed for the prediction, two-fold discontinuity must be admitted: loss of coherence with potential measurements, and renormalization from the results of actual measurements.
NONLOCAL MEASUREMENTS IN THE TIME-SYMMETRIC QUANTUM MECHANICS
Authors: VAIDMAN LEV , NEVO IZHAR
Published: May 2006

Although for some nonlocal variables the standard quantum measurements which are reliable, instantaneous, and nondemolition, are impossible, demolition reliable instantaneous measurements of all variables are possible. It is shown that this is correct also in the framework of the time-symmetric quantum formalism, i.e. nonlocal variables of composite quantum systems with quantum states evolving both forward and backward in time are measurable in a demolition way. The result follows from the possibility to reverse with certainty the time direction of backward evolving quantum states.
SQUEEZING AND FIBER-OPTIC COMMUNICATIONS
Authors: VASILYEV MICHAEL , STELMAKH NIKOLAI
Published: May 2006

We review the relations between squeezing and optical communication advances and introduce the field of distributed phase-sensitive amplification, where we expect this cross-fertilization to happen next. We consider the quantum noise properties of phase-sensitive amplifiers in lossy fiber in the case of arbitrary parametric gain distribution along the fiber length. Three most important cases of gain followed by loss, loss followed by gain, and ideally distributed gain, are discussed in detail. We show that ideally distributed phase-sensitive amplifier maximizes the signal-to-noise ratio for a fixed non-linear phase shift in the fiber span, and is promising for both classical and quantum communications.
CONDITIONAL GENERATION OF TWIN SUB-POISSONIAN BEAMS VIA POST-SELECTION
Authors: ZHANG YUN , HAYASAKA KAZUHIRO , KASAI KATSUYUKI
Published: May 2006

We report the experimental demonstration of generation of twin sub-Poissonian beams by using a conditional preparation technique. By this simple technique, we generate twin sub-Poissonian beams with a quantum correlation of 4.0 ± 0.2 dB between two sub-Poissonian beams of 4.0 ± 0.3 dB noise reductions from two sets of initially independent twin beams, each characterized by intensity-difference squeezing of 7.0 ± 0.3 dB.
QUANTUM STORAGE AND CLONING OF LIGHT STATES IN EIT-LIKE MEDIUM
Authors: ALODJANTS A. P. , ARAKELIAN S. M.
Published: May 2006

In the paper we consider a new approach for storage and cloning of quantum information by three level atomic (molecular) systems in the presence of the electromagnetically induced transparency (EIT) effect. For that, the various schemes of transformation into the bright and dark polaritons for quantum states of optical field in the medium are proposed. Physical conditions of realization of quantum nondemolition (QND) storage of quantum optical state are formulated for the first time. We have shown that the best storage and cloning of can be achieved with the atomic ensemble in the Bose-Einstein condensation state. We discuss stimulated Raman two-color photoassociation for experimental realization of the schemes under consideration.
MASER OSCILLATION FROM ELECTRONIC SPIN RESONANCE IN A CRYOGENIC SAPPHIRE FREQUENCY STANDARD
Authors: BOURGEOIS P.-Y. , OXBORROW M. , TOBAR M. E. , BAZIN N. , KERSALÉ Y. , GIORDANO V.
Published: May 2006

We report the first observation of an Fe3+ maser oscillation at zero magnetic field inside a whispering gallery (WG) sapphire resonator. The described maser is new in that it operates at zero-field and with low ion concentration. At zero-field, the Fe3+ ion shows a 3-level structure related to the electron spin resonance (ESR). By applying a 31 GHz pump (|1/2〉 → |5/2〉), the ion operates as a maser at 12 GHz (|5/2〉 → |3/2〉). The maser effect is made possible by the high Q-factor (several 108) of the cryogenic whispering gallery resonator. Additionnaly, the sharp cavity resonance provides short term stability. Preliminary measurements indicate a frequency stability of parts in 10-14 (Allan deviation at 100 s), still limited by the instrument. The ultimate maser stability is still unknown.
SQUEEZED VACUUM AND TRANSVERSE FIELD EFFECTS IN A THREE-LEVEL BISTABLE MODEL
Authors: SHARABY Y. A. , HASSAN S. S. , MAIZE S. M. A.
Published: May 2006

Optical bistability for three-level V-type atomic medium in ring cavity is examined in the presence of squeezed vacuum field within and without plane wave approximations. Squeezed Vacuum parameters affects the steady state behavior of the system. Gaussian field feature causes a significant change in the steady state behavior.
LIGHT PROPAGATION IN ORDERED AND RANDOM ONE-DIMENSIONAL SYSTEMS BY CAVITY FORMATION
Authors: MAROUF S. , ZEKRI N.
Published: May 2006

We study how the light transport behavior evolves when a one-dimensional (1-D) system changes continuously from a perfectly ordered structure to a highly disordered structure. The introduction of randomness to a periodic structure enhances light localization in frequency regions in which it is delocalized in a periodic structure. To better understand the phenomenon and further investigate how the cavity is formed, we conduct a systematic study of the impact of the material and geometric properties of a random medium on the performance of random lasers; in a completely random system, a resonant cavity is formed by two stacks of multiple layers which serve as two highly reflective broadband mirrors. We calculate the size and the quality factor of 1-D random cavities.
TEMPORAL ATOMIC BEAM-SPLITTER AND ATOMIC HOMODYNE DETECTION ON TWO-MODE BOSE–EINSTEIN CONDENSATES
Authors: DA CUNHA B. R. , DE OLIVEIRA M. C.
Published: May 2006

The Rabi regime for a Bose-Einstein condensate (BEC) in double-well potential occurring for sufficiently strong cross-collision strengths is analyzed. It is shown that in this regime the potential barrier acts as a temporal atomic beam splitter. An ideal 50:50 atomic beam splitter reached at specific intervals of time is employed for a balanced homodyne detection of the condensate relative phase.
A SINGLE-ION STOCHASTIC QUANTUM PROCESSOR
Authors: BLACKBURN PAUL , ORSZAG MIGUEL
Published: May 2006

We propose a scheme for implementing a single-ion Stochastic Quantum Processor using a single cold trapped ion. The processor implements an arbitrary rotation around the z axis of the Bloch sphere of a data qubit, given two program qubits, that is, the operation realized on the data is determined by using different program qubits and not by varying the gate itself. Unfortunately this cannot be done deterministically, and must be necessarily stochastic. In this proposal the operation is applied successfully with probability p = 3/4.
EFFECT OF HIGHER ORDER ENERGY CORRECTIONS INCLUDING THREE-BODY INTERACTION ON THE BOSE-EINSTEIN CONDENSATE WITH THE VARIATION OF REPULSIVE SELF INTERACTION ENERGY
Authors: TEWARI SHRI PRAKASH , SILOTIA POONAM , SAXENA ADITYA , GUPTA LOKESH KUMAR
Published: May 2006

Various ground state properties such as chemical potential, differential and total energy per particle etc. of Bose-Einstein condensate of 10000 85 Rb atoms with varying repulsive self-interaction energy have been reported considering not only two-body interaction but also including the higher order terms of the low-density energy expansion of homogeneous Bose gas in the Ginzburg, Pitaevskii and Gross (GPG) equation. These include hard-core approximation of the bosons neglected earlier and the three-body interaction terms. The study is more general as it includes the terms beyond logarithm in energy density expansion. It is also shown that such a consideration does not violate the lower bound predicted earlier in which the 'constant' beyond logarithm term in the three-body interaction was neglected.
QUBIT DECOHERENCE IN A NUCLEAR MAGNETIC RESONANCE-LIKE QUANTUM PROCESSOR WITH TRAPPED PARTICLES
Authors: CIARAMICOLI G. , MARZOLI I. , TOMBESI P.
Published: May 2006

We present an in-depth analysis of a potentially significant source of decoherence for a quantum processor, we proposed in our previous paper.1 The processor consists of an array of charged particles confined in planar micro-Penning traps. Qubits are encoded in the particle spins, that are mutually coupled as nuclear spins in a nuclear magnetic resonance-molecule. In this paper, we study in detail the de-phasing effect on the qubit dynamics produced by thermal excitations in the cyclotron motion of the particles.
QUANTUM KALEIDOSCOPES AND BELL'S THEOREM
Authors: ARAVIND P. K.
Published: May 2006

A quantum kaleidoscope is defined as a set of observables, or states, consisting of many different subsets that provide closely related proofs of the Bell-Kochen-Specker (BKS) and Bell nonlocality theorems. The kaleidoscopes prove the BKS theorem through a simple parity argument, which also doubles as a proof of Bell's nonlocality theorem if use is made of the right sort of entanglement. Three closely related kaleidoscopes are introduced and discussed in this paper: a 15-observable kaleidoscope, a 24-state kaleidoscope and a 60-state kaleidoscope. The close relationship of these kaleidoscopes to a configuration of 12 points and 16 lines known as Reye's configuration is pointed out. The "rotations" needed to make each kaleidoscope yield all its apparitions are laid out. The 60-state kaleidoscope, whose underlying geometrical structure is that of ten interlinked Reyes' configurations (together with their duals), possesses a total of 1120 apparitions that provide proofs of the two Bell theorems. Some applications of these kaleidoscopes to problems in quantum tomography and quantum state estimation are discussed.
ABOUT THE MEAN KING'S PROBLEM AND DISCRETE WIGNER DISTRIBUTIONS
Authors: DURT THOMAS
Published: May 2006

When the state of a quantum system belongs to a N-dimensional Hilbert space, with N the power of a prime number, it is possible to associate to the system a finite field (Galois field) with N elements. In this paper, we introduce generalized Bell states that can be intrinsically expressed in terms of the field operations. These Bell states are in one to one correspondence with the N2elements of the generalised Pauli group or Heisenberg-Weyl group. This group consists of discrete displacement operators and provides a discrete realisation of the Weyl function. Thanks to the properties of generalised Bell states and of quadratic extensions of finite fields, we derive a particular solution for the Mean King's problem. This solution is in turn shown to be in one to one correspondence with a set of N2self-adjoint operators that provides a discrete realisation of the Wigner quasi-distribution.
FINITE DIMENSIONAL QUANTIZATIONS OF THE (q,p) PLANE: NEW SPACE AND MOMENTUM (OR QUADRATURES) INEQUALITIES
Authors: GAZEAU JEAN-PIERRE , MICHAUX FRANCOIS-XAVIER , MONCEAU PASCAL
Published: May 2006

We present a N-dimensional quantization à la Berezin-Klauder or frame quantization of the complex plane based on overcomplete families of states (coherent states) generated by the N first number eigenstates. The spectra of position and momentum operators (or of quadrature operators in quantum optics) are finite and eigenvalues are equal, up to a factor, to the zeros of Hermite polynomials. From numerical and theoretical studies of the large N behavior of the product λm(N) λM(N) of non null smallest positive and largest eigenvalues, we infer the inequality [Formula: see text] (resp. [Formula: see text]) involving, in suitable units, the minimal (δN(Q)) and maximal (ΔN(Q)) sizes of regions of space (resp. momentum) which are accessible to exploration within this finite-dimensional quantum framework. Interesting issues on the measurement process and connections with the finite Chern-Simons matrix model for the Quantum Hall effect are discussed.
A SU(2) RECIPE FOR MUTUALLY UNBIASED BASES
Authors: KIBLER MAURICE R. , PLANAT MICHEL
Published: May 2006

A simple recipe for generating a complete set of mutually unbiased bases in dimension 2j + 1, with 2j integer and 2j + 1 prime, is developed from a single matrix Va acting on a space of constant angular momentum j and defined in terms of the irreducible characters of the cyclic group C2j + 1. This recipe yields an (apparently new) compact formula for the vectors spanning the various mutually unbiased bases. In dimension (2j + 1)e, with 2j integer, 2j + 1 prime and e positive integer, the use of direct products of matrices of type Va makes it possible to generate mutually unbiased bases. As two pending results, the matrix Va is used in the derivation of a polar decomposition of SU (2) and of a FFZ algebra.
(ANTI)COMMUTATIVITY OF THE HARMONIC CREATION AND ANNIHILATION OPERATORS
Authors: KUWATA S. , MARUMOTO A.
Published: May 2006

It is known that para-particles, together with fermions and bosons, of a single mode can be described as an irreducible representation of the Lie (super) algebra 𝔰𝔩2(ℂ) (2-dimensional special linear algebra over the complex number ℂ), that is, they satisfy the equation of motion of a harmonic oscillator. Under the equation of motion of a harmonic oscillator, we obtain the set of the commutation relations which is isomorphic to the irreducible representation, to find that the equation of motion, conversely, can be derived from the commutation relation only for the case of either fermion or boson. If Nature admits of the existence of such a sufficient condition for the equation of motion of a harmonic oscillator, no para-particle can be allowed.
MONODROMY ARISING FROM THE MARKOFF THEORY
Authors: PERRINE SERGE
Published: May 2006

In a former work, recalling what the Markoff theory is, we summarized some existing links with the group GL(2, ℤ) of 2 × 2 matrices. We also quoted the relation with conformal punctured toruses. The monodromy representation of the Poincaré group of such a torus was considered. Here we explicit the corresponding solution of the associated Riemann-Hilbert problem, and the resulting Fuchs differential equation. We precisely describe how the calculus runs. The main result is the description of a complete family of Fuchs differential equations with, as the monodromy group, the free group with two generators. We also identify a link with some eigenvalues of a Laplacian. The introduction explains the links that we see with information and computation theory (classical or quantum).
HUYGHENS, BOHR, RIEMANN AND GALOIS: PHASE-LOCKING
Authors: PLANAT MICHEL
Published: May 2006

Several mathematical frameworks of phase-locking are developed. The classical Huyghens approach is generalized to include all harmonic and subharmonic resonances and is found to be connected to 1/f noise and prime number theory. Two types of quantum phase-locking operators are defined, one acting on the rational numbers, the other on the elements of a Galois field. In both cases we analyse in detail the phase properties and find that they are related to the Riemann zeta function and to incomplete Gauss sums, respectively.