Quantum Dissension: Generalizing Quantum Discord for Three-Qubit States

We introduce the notion of quantum dissension for a three-qubit system as a measure of quantum correlations. We use three equivalent expressions of three-variable mutual information. Their differences can be zero classically but not so in quantum domain. It generalizes the notion of quantum discord to a multipartite system. There can be multiple definitions of the dissension depending on the nature of projective measurements done on the subsystems. As an illustration, we explore the consequences of these multiple definitions and compare them for three-qubit pure and mixed GHZ and W states. We find that unlike discord, dissension can be negative. This is because measurement on a subsystem may enhance the correlations in the rest of the system. This approach can pave a way to generalize the notion of quantum correlations in the multiparticle setting.Comment: 9 pages 6 figures typo fixed and some arguments adde

Effect of continuum couplings in fusion of halo 11^{11}Be on 208^{208}Pb around the Coulomb barrier

The effect of continuum couplings in the fusion of the halo nucleus $^{11}$Be on $^{208}$Pb around the Coulomb barrier is studied using a three-body model within a coupled discretised continuum channels (CDCC) formalism. We investigate in particular the role of continuum-continuum couplings. These are found to hinder total, complete and incomplete fusion processes. Couplings to the projectile $1p_{1/2}$ bound excited state redistribute the complete and incomplete fusion cross sections, but the total fusion cross section remains nearly constant. Results show that continuum-continuum couplings enhance the irreversibility of breakup and reduce the flux that penetrates the Coulomb barrier. Converged total fusion cross sections agree with the experimental ones for energies around the Coulomb barrier, but underestimate those for energies well above the Coulomb barrier.Comment: 15 pages, 7 figures, accepted in Phys. Rev.

Phenomenological constraints on SUSY SU(5) GUTs with non-universal gaugino masses

We study phenomenological aspects of supersymmetric SU(5) grand unified theories with non-universal gaugino masses. For large tan beta, we investigate constraints from the requirement of successful electroweak symmetry breaking, the positivity of stau mass squared and the b to s gamma decay rate. In the allowed region, the nature of the lightest supersymmetric particle is determined. Examples of mass spectra are given. We also calculate loop corrections to the bottom mass due to superpartners.Comment: 10 pages, 2 figures (8 eps files), uses REVTeX. Replaced to match the version to be published in PRD: minor corrections and addition

Transmission-electron-microscopy study of charge-stripe order in La(1.725)Sr(0.275)NiO(4)

We characterize the local structure and correlations of charge stripes in La(1.725)Sr(0.275)NiO(4) using transmission-electron microscopy. We present direct evidence that the stripe modulation is indeed one-dimensional within each NiO(2) plane. Furthermore, we show that individual stripes tend to be either site-centered or bond-centered, with a bias towards the former. The spacing between stripes often fluctuates about the mean, contributing to a certain degree of frustration of the approximate body-centered stacking along the c-axis. These results confirm ideas inferred from previous neutron-diffraction measurements on doped nickelates, and demonstrate that charge-stripe order is quite different from the conventional concept of charge-density-wave order.Comment: 5 pages, 6 figures, submitted to PR

Sub- and above barrier fusion of loosely bound 6^6Li with 28^{28}Si

Fusion excitation functions are measured for the system $^6$Li+$^{28}$Si using the characteristic $\gamma$-ray method, encompassing both the sub-barrier and above barrier regions, viz., $E_{lab}$= 7-24 MeV. Two separate experiments were performed, one for the above barrier region ($E_{lab}$= 11-24 MeV) and another for the below barrier region ($E_{lab}$= 7-10 MeV). The results were compared with our previously measured fusion cross section for the $^7$Li+$^{28}$Si system. We observed enhancement of fusion cross section at sub-barrier regions for both $^6$Li and $^7$Li, but yield was substantially larger for $^6$Li. However, for well above barrier regions, similar type of suppression was identified for both the systems.Comment: 8 pages, 6 figures, as accepted for publication in Eur.Phys.J.

Recent experimental results in sub- and near-barrier heavy ion fusion reactions

Recent advances obtained in the field of near and sub-barrier heavy-ion fusion reactions are reviewed. Emphasis is given to the results obtained in the last decade, and focus will be mainly on the experimental work performed concerning the influence of transfer channels on fusion cross sections and the hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier fusion taught us that cross sections may strongly depend on the low-energy collective modes of the colliding nuclei, and, possibly, on couplings to transfer channels. The coupled-channels (CC) model has been quite successful in the interpretation of the experimental evidences. Fusion barrier distributions often yield the fingerprint of the relevant coupled channels. Recent results obtained by using radioactive beams are reported. At deep sub-barrier energies, the slope of the excitation function in a semi-logarithmic plot keeps increasing in many cases and standard CC calculations over-predict the cross sections. This was named a hindrance phenomenon, and its physical origin is still a matter of debate. Recent theoretical developments suggest that this effect, at least partially, may be a consequence of the Pauli exclusion principle. The hindrance may have far-reaching consequences in astrophysics where fusion of light systems determines stellar evolution during the carbon and oxygen burning stages, and yields important information for exotic reactions that take place in the inner crust of accreting neutron stars.Comment: 40 pages, 63 figures, review paper accepted for EPJ

Muon anomalous magnetic moment in the standard model with two Higgs doublets

The muon anomalous magnetic moment is investigated in the standard model with two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all the effective Yukawa couplings become complex. As a consequence of the non-zero phase in the couplings, the one loop contribution from the neutral scalar bosons could be positive and negative relying on the CP phases. The interference between one and two loop diagrams can be constructive in a large parameter space of CP-phases. This will result in a significant contribution to muon anomalous magnetic moment even in the flavor conserving process with a heavy neutral scalar boson ($m_h \sim$ 200 GeV) once the effective muon Yukawa coupling is large ($|\xi_\mu|\sim 50$). In general, the one loop contributions from lepton flavor changing scalar interactions become more important. In particular, when all contributions are positive in a reasonable parameter space of CP phases, the recently reported 2.6 sigma experiment vs. theory deviation can be easily explained even for a heavy scalar boson with a relative small Yukawa coupling in the S2HDM.Comment: 8 pages, RevTex file, 5 figures, published version Phys. Rev. D 54 (2001) 11501

On the operando structure of ruthenium oxides during the oxygen evolution reaction in acidic media

In the search for rational design strategies for oxygenevolutionreaction (OER) catalysts, linking the catalyst structure to activityand stability is key. However, highly active catalysts such as IrO x and RuO x undergostructural changes under OER conditions, and hence, structure-activity-stabilityrelationships need to take into account the operando structure ofthe catalyst. Under the highly anodic conditions of the oxygen evolutionreaction (OER), electrocatalysts are often converted into an activeform. Here, we studied this activation for amorphous and crystallineruthenium oxide using X-ray absorption spectroscopy (XAS) and electrochemicalscanning electron microscopy (EC-SEM). We tracked the evolution ofsurface oxygen species in ruthenium oxides while in parallel mappingthe oxidation state of the Ru atoms to draw a complete picture ofthe oxidation events that lead to the OER active structure. Our datashow that a large fraction of the OH groups in the oxide are deprotonatedunder OER conditions, leading to a highly oxidized active material.The oxidation is centered not only on the Ru atoms but also on theoxygen lattice. This oxygen lattice activation is particularly strongfor amorphous RuO x . We propose that thisproperty is key for the high activity and low stability observed foramorphous ruthenium oxide.Catalysis and Surface Chemistr

Phase diagram of the La1−x_{1-x}Cax_{x}MnO3_{3} compound for 0.5≤x≤0.90.5\leq x\leq 0.9

We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry $Pnma$. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On further cooling the material passes to an antiferromagnetic ground state with Neel temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural transformation occurs at the same temperature as the magnetic transition. Overall, the neutron diffraction patterns were explained by considering four phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at x=1. Between these phase boundaries the magnetic reflections suggest the existence of mixed compounds containing both phases of the adjacent phase boundaries in a ratio determined by the lever rule