Showing papers in "European Physical Journal D in 2007"

Unconditional security of practical quantum key distribution

Abstract: We present a complete protocol for BB84 quantum key distribution for a realistic setting (noise, loss, multi-photon signals of the source) that covers many of todays experimental implementations. The security of this protocol is shown against an eavesdropper having unrestricted power to manipulate the signals coherently on their path from sender to receiver. The protocol and the security proof take into account the effects concerning the finite size of the generated key. This paper is identical to the preprint arXiv:quant-ph/0107017, which was finalized in 2001. Therefore, some of the more recent developments, including the question of composability, are not addressed.

The colours of nanometric gold-Optical response functions of selected gold-cluster thiolates

Abstract: A set of broad-range NIR-vis-UV optical absorption spectra, measured for selected gold-cluster thiolate compounds (GCTs, containing ~20 to 300 Au atoms), is consistently displayed and then analyzed within the dielectric-functions approach. The size-evolution toward `bulk' (Au diameter >3-nm) optical response is thereby clearly demonstrated. The emergence of apparent energy gaps, Eon, for onset of optical absorption, as well as other fine-structure, is consistent with that of a well-quantized metallic electronic structure for the compounds' cores: the onset-band's location Eon and intensity are attributed semiclassically to a circulation-frequency resonance of the Fermi-level electrons. With decreasing cluster-size, an increasing fraction of the integrated (sum-rule) intensity is `missing' from the <4 eV region. This might be explained by the outermost layer consisting of Au(I)thiolate complexes.

Quantum state sharing of an arbitrary multiqubit state using nonmaximally entangled GHZ states

Abstract: We explicitly present a scheme for quantum state sharing of an arbitrary multiqubit state using nonmaximally entangled GHZ states as the quantum channel and generalized Bell states as the measurement basis. The scheme succeeds only probabilistically with its total success probability depending on the degree of entanglement matching between the quantum channel and the generalized Bell states. Security of the scheme is guaranteed by the fact that attacks of an outside eavesdropper or/and an inside dishonest party will inevitably introduce detectable errors.

Inertial fusion research in China

Abstract: The goal of the first milestone of the inertial fusion program in China is to reach fusion ignition and plasma burning in about 2020. Under the program, in the past years, the inertial fusion physics research achieved great progress; the laser facilities and the support technologies for laser drivers are advanced; the advanced diagnostic techniques are developed and the relatively integrated system is set up; the precise target fabrications are coordinately developed.

QED and relativistic corrections in superheavy elements

Abstract: In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Lande g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.

Towards direct mass measurements of nobelium at SHIPTRAP

Abstract: The Penning-trap mass spectrometer SHIPTRAP allows precision mass measurements of rare isotopes produced in fusion-evaporation reactions. In the first period of operation the masses of more than 50 neutron-deficient radionuclides have been measured. In this paper the perspectives for direct mass measurements of rare isotopes around nobelium are discussed and the achievable precision is addressed. The temporal stability of the magnetic field, an important issue for the long measurement times resulting from the low production rates, was investigated and the time-dependent uncertainty due to magnetic field fluctuations was determined. Based on the present performance direct mass measurements of nobelium isotopes are already feasible. With several technical improvements heavier elements between Z=102–105 will be in reach.

Streaming instability in quantum dusty plasmas

Abstract: By using a quantum hydrodynamic (QHD) model, we derive a generalized dielectric constant for an unmagnetized quantum dusty plasma composed of electrons, ions, and charged dust particulates. Neglecting the electron inertial force in comparison with the electron pressure, and the force associated with the electron correlations at a quantum scale, we discuss two classes of electrostatic instabilities that are produced by streaming ions, and dust grains. The effects of the plasma streaming speeds, the thermal speed of electrons, and the quantum parameter are examined on the growth rates. The relevance of our investigation to dense astrophysical plasmas is discussed.

Spectroscopic studies of laser induced aluminum plasma using fundamental, second and third harmonics of a Nd:YAG laser

Abstract: In the present work, we have studied the spatial evolution of the aluminum plasma produced by the fundamental (1064 nm), second (532 nm) and third (355 nm) harmonics of a Q-switched pulsed Nd:YAG laser. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using Boltzmann plot method whereas the electron number density has been determined from the Stark broadened profiles. Besides we have studied the variation of excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure. In addition, we have performed quantitative analysis of photon absorption and vapor ionization mechanism at three laser wavelengths and estimated the inverse bremsstrahlung (IB) absorption and photoionization (PI) coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the experimental results.

Three-party qutrit-state sharing

Abstract: A three-party scheme for securely sharing an arbitrary unknown single-qutrit state is presented. Using a generalized Greenberger-Horne-Zeilinger (GHZ) state as the quantum channel among the three parties, the quantum information (i.e. the qutrit state) from the sender can be split in such a way that the information can be recovered if and only if both receivers collaborate. A generalization of the scheme to multi-party case is also sketched.

Structural properties of amorphous TiO2 nanoparticles

Abstract: Structural properties of amorphous TiO2 spherical nanoparticles have been studied in models with different sizes of 2 nm, 3 nm, 4 nm and 5 nm under non-periodic boundary conditions. We use the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of an amorphous nanoparticle obtained at 350 K have been analyzed in detail through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Moreover, we show the radial density profile in a nanoparticle. Calculations show that size effects on structure of a model are significant and that if the size is larger than 3 nm, amorphous TiO2 nanoparticles have a distorted octahedral network structure with the mean coordination number ZTi-O ≈6.0 and ZO-Ti ≈3.0 like those observed in the bulk. Surface structure and surface energy of nanoparticles have been obtained and presented.

Geometric magic numbers of sodium clusters: Interpretation of the melting behaviour

Abstract: Putative global minima of sodium clusters with up to 380 atoms have been located for two model interatomic potentials in order to identify the structures responsible for the size-dependence of the thermodynamic properties in experiments. Structures based upon the Mackay icosahedra predominate for both potentials, and the magic numbers for the Murrell-Mottram model show excellent agreement with the sizes at which maxima in the latent heat and entropy change at melting have been found in experiment. In particular, the magic numbers at sizes intermediate between the complete Mackay icosahedra are due to unusual twisted icosahedral structures.

Optical extinction spectroscopy of single silver nanoparticles

Abstract: The extinction spectrum of single silver nanoparticles with size ranging from 20 to 80 nm is investigated with the spatial modulation spectroscopy technique using either a tunable laser or a white lamp as the broadband source. Results are in good agreement with the prediction of the Mie theory, permitting to extract the nanoparticle size from the measured absolute value of the optical extinction cross-section. In contrast, the deduced refractive index of the nanoparticle environment and the reduction of the electron mean free path show a large dependence on the precise value of the bulk silver dielectric function.

The megajoule laser program — ignition at hand

Abstract: The French Commissariat a l'Energie Atomique (CEA) is currently building the Laser MegaJoule (LMJ), a 240-beam laser facility, at the CEA Laboratory CESTA near Bordeaux. LMJ will be a cornerstone of CEA's “Programme Simulation”, the French Stockpile Stewardship Program. LMJ is designed to deliver about 2 MJ of 0.35 μm light to targets for high energy density physics experiments, among which fusion experiments. LMJ technological choices were validated with the Ligne d'Integration Laser (LIL), a scale 1 prototype of one LMJ bundle, built at CEA/CESTA. Plasma experiments started at the end of 2004 on LIL, which is already open to the scientific community through the Plasma and Lasers Institute. The construction of the LMJ building itself started in March of 2003. LMJ will be gradually commissioned from early 2011, and after an experimental program to progress toward fusion, the first fusion experiments will begin late 2012.

Frenkel-Kontorova model with cold trapped ions

Abstract: We study analytically and numerically the properties of one-dimensional chain of cold ions placed in a periodic potential of optical lattice and global harmonic potential of a trap. In close similarity with the Frenkel-Kontorova model, a transition from sliding to pinned phase takes place with the increase of the optical lattice potential for the density of ions incommensurate with the lattice period. We show that at zero temperature the quantum fluctuations lead to a quantum phase transition and melting of pinned instanton glass phase at large values of dimensional Planck constant. After melting the ion chain can slide in an optical lattice. The obtained results are also relevant for a Wigner crystal placed in a periodic potential.

Copper and copper oxide nanoparticles in a cellulose support studied using anomalous small-angle X-ray scattering

Abstract: Microcrystalline cellulose is a porous natural material which can be used both as a support for nanoparticles and as a reducer of metal ions. Cellulose supported nanoparticles can act as catalysts in many reactions. Cu, CuO, and Cu2O particles were prepared in microcrystalline cellulose by adding a solution of copper salt to the insoluble cellulose matrix and by reducing the copper ions with several reducers. The porous nanocomposites were studied using anomalous small angle X-ray scattering (ASAXS), X-ray absorption spectroscopy, and X-ray diffraction. Reduction of Cu2+ with cellulose in ammonium hydrate medium yielded crystalline CuO nanoparticles and the crystallite size was about 6–20 nm irrespective of the copper concentration. The size distribution of the CuO particles was determined with ASAXS measurements and coincided with the crystallite sizes. Using sodium borohydrate or hydrazine sulfate as a reducer both metallic Cu and Cu2O nanoparticles were obtained and the crystallite size and the oxidation state depended on the amount of reducer.

Influence of lasers propagation delay on the sensitivity of atom interferometers

Abstract: In atom interferometers based on two photon transitions, the delay induced by the difference of the laser beams paths makes the interferometer sensitive to the fluctuations of the frequency of the lasers. We first study, in the general case, how the laser frequency noise affects the performance of the interferometer measurement. Our calculations are compared with the measurements performed on our cold atom gravimeter based on stimulated Raman transitions. We finally extend this study to the case of cold atom gradiometers.

Rings, towers, cages of ZnO

Abstract: Theoretical electronic structure studies on (ZnO)n (n= 2–18, 21) have been carried out to show that the transition from an elementary ZnO molecule to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our first principles electronic structure calculations carried out within a gradient corrected density functional framework show that small ZnnOn (n=2–7) clusters form single, highly stable rings. Zn3O3 and the symmetric cage Zn12O12 are shown to be particularly stable clusters. Among larger clusters, the most stable are oblong cages, Zn15O15, Zn18O18, and Zn21O21, which are reminiscent of nanotubes.

Modulational instability of electron-acoustic waves: an application to auroral zone plasma

Abstract: By using the standard reductive perturbation technique, a nonlinear Schrodinger equation is derived to study the modulational instability of finite amplitude electron-acoustic waves in an unmagnetized plasma consisting of cold electron fluid and nonthermal electrons. It is found that the presence of nonthermally distributed electrons modifies the domain of the modulational instability and solitary structures. Possibility of stationary states of the wave packets that can appear as envelope solitons under different conditions is explored. The present investigation is relevant to observation from the Viking satellite in the dayside auroral zone.

Non-equilibrium electron and phonon dynamics in metals under femtosecond laser pulses

Abstract: Different models for relaxation dynamics of electrons and phonons in a thin metal film heated by femto-pico second laser pulses have been discussed. The traditional two-temperature approach reveals to be inaccurate due to deviations of electrons and phonons from Fermi-Dirac and Bose-Einstein distributions, respectively. Coupled Boltzmann kinetic equations have been adapted for the quantum statistics to study the energy distribution of electrons and phonons in metals. Theoretical details have been discussed and a new solution method has been proposed overcoming numerical problems and improving stability, allowing the study of the dynamics until the complete relaxation. Numerical results have been compared with photoemission spectroscopy experimental data.

Catalyst poisoning in the conversion of CO and N 2 O to CO 2 and N 2 on Pt 4 - in the gas phase

Abstract: Pt4 - catalyses the conversion of CO and N2O to CO2 and N2 in the gas phase, as observed by Fourier transform ion cyclotron (FT-ICR) mass spectrometry. The partial pressures of CO and N2O determine the extent of poisoning and the turnover numbers that can be achieved. The catalytic conversion terminates as soon as two CO are adsorbed on the cluster. With N2O, the reactivity of Pt4O2 - and Pt4O3 - is reduced to 41% and 34% compared to Pt4O-, respectively, and with Pt4O4 - this value is reduced to 1%. In contrast, Pt4 + shows no apparent catalytic activity. Density functional theory calculations of Pt4 +/- with CO and N2O adsorbates reveal significantly different stabilities of the reaction intermediates for the different charge states.

Transition energies of atomic lawrencium

Abstract: Transition energies of the superheavy element lawrencium, including the ionization potential, excitation energies and electron affinities, are calculated by the intermediate Hamiltonian coupled cluster method. A large basis set (37s31p26d21f16g11h6i) is used, as well as an extensive P space (6s5p4d2f1g). The outer 43 electrons are correlated. Accuracy is monitored by applying the same approach to lutetium, the lighter homologue of Lr, and comparing with experimentally known energies. QED corrections are included. The main goal is to predict excitation energies, in anticipation of planned spectroscopy of Lr. The ground state of Lr is $7s^27p\ ^2{\rm P}_{1/2}$ , unlike the $5d6s^2\ ^2{\rm D}_{3/2}$ of Lu. Predicted Lr excitations with large transition moments in the prime range for the planned experiment, 20 000–30 000 cm-1, are 7p→8s at 20 100 cm-1 and 7p→7d at 28 100 cm-1. The average absolute error of 20 excitation energies of Lu is 423 cm -1, and the error limits for Lr are put at 700 cm-1. The two electron affinities measured recently for Lu are reproduced within 55 cm-1, and a third bound state of Lu- is predicted.

Entanglement dynamics under decoherence: from qubits to qudits

Abstract: We investigate the time evolution of entanglement for bipartite systems of arbitrary dimensions under the influence of decoherence. For qubits, we determine the precise entanglement decay rates under different system-environment couplings, including finite temperature effects. For qudits, we show how to obtain upper bounds for the decay rates and also present exact solutions for various classes of states.

Quantum dynamics of bosons in a double-well potential: Josephson oscillations, self-trapping and ultralong tunneling times

Abstract: The dynamics of the population imbalance of bosons in a double-well potential is investigated from the point of view of many-body quantum mechanics in the framework of the two-mode model. For small initial population imbalances, coherent superpositions of almost equally spaced energy eigenstates lead to Josephson oscillations. The suppression of tunneling at population imbalances beyond a critical value is related to a high concentration of initial state population in the region of the energy spectrum with quasi-degenerate doublets. Negligible coherences among adjacent doublets result in imbalance oscillations with a very small amplitude. For unaccessible long times, however, the system recovers the regime of Josephson oscillations.

Impact broadening of alkali lines in brown dwarfs

Abstract: Spectral line widths of the light alkalies are presented for conditions prevailing in brown dwarf atmospheres. A unified line shape theory and a set of pseudopotentials are used to compute widths of Li, Na, and K resonance lines perturbed by He and H2. While limited available experimental data confirm the trends found in the theoretical values reported here, they suggest that improved potentials are needed. PACS. 32.70.Jz Line shapes, widths, and shifts

Carbon-cluster mass calibration at SHIPTRAP

Abstract: A carbon-cluster ion source has been installed and tested at SHIPTRAP, the Penning-trap mass spectrometer for precision mass measurements of heavy elements at GSI. Carbon-cluster ions 12Cn +, 5 ≤n ≤23, were produced by laser-induced desorption and ionization from a carbon sample. They were tested for the first time as reference ions in an on-line mass measurement of the radionuclides 144Dy, 146Dy and 147Ho. In addition, carbon clusters of various sizes were used for an investigation of the systematic uncertainty of SHIPTRAP covering a mass range from 84 u to 240 u. The mass-dependent uncertainty was found to be negligible for the case of (m-m ref)< 100 u. However, a systematic uncertainty of 4.5 ×10-8 was revealed.

The national ignition facility: path to ignition in the laboratory

Abstract: The National Ignition Facility (NIF) is a 192-beam laser facility presently under construction at LLNL. When completed, NIF will be a 1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion ignition and to perform high energy density experiments in support of the US nuclear weapons stockpile. Four of the NIF beams have been commissioned to demonstrate laser performance and to commission the target area including target and beam alignment and laser timing. During this time, NIF demonstrated on a single-beam basis that it will meet its performance goals and demonstrated its precision and flexibility for pulse shaping, pointing, timing and beam conditioning. It also performed four important experiments for Inertial Confinement Fusion and High Energy Density Science. Presently, the project is installing production hardware to complete the project in 2009 with the goal to begin ignition experiments in 2010. An integrated plan has been developed including the NIF operations, user equipment such as diagnostics and cryogenic target capability, and experiments and calculations to meet this goal. This talk will provide NIF status, the plan to complete NIF, and the path to ignition.

A quantum trajectory description of decoherence

Abstract: A complete theoretical treatment in many problems relevant to physics, chemistry, and biology requires considering the action of the environment over the system of interest. Usually the environment involves a relatively large number of degrees of freedom, this making the problem numerically intractable from a purely quantum-mechanical point of view. To overcome this drawback, a new class of quantum trajectories is proposed. These trajectories, based on the same grounds as Bohmian ones, are solely associated to the system reduced density matrix, since the evolution of the environment degrees of freedom is not considered explicitly. Within this approach, environment effects come into play through a time-dependent damping factor that appears in the system equations of motion. Apart from their evident computational advantage, this type of trajectories also results very insightful to understand the system decoherence. In particular, here we show the usefulness of these trajectories analyzing decoherence effects in interference phenomena, taking as a working model the well-known double-slit experiment.

C++QED: an object-oriented framework for wave-function simulations of cavity QED systems

Abstract: We present a framework for efficiently performing Monte Carlo wave-function simulations in cavity QED with moving particles. It relies heavily on the object-oriented programming paradigm as realised in C++, and is extensible and applicable for simulating open interacting qua ntum dynamics in general. The user is provided with a number of “elements”, e.g. pumped moving particles, pumped lossy cavity modes, and various interactions to compose complex interacting systems, which contain several particles moving in electromagnetic fields of various configurations, and perform wave-function simulations on such systems. A number of tools are provided to facilitate the implementation of new elements.

Theoretical study of structure and segregation in 38-atom Ag-Au nanoalloys

Abstract: Ag–Au bimetallic “nanoalloy” clusters with 38 atoms have been studied using a Gupta many-body potential combined with a genetic algorithm search technique. Clear changes in structure are observed as a function of Ag/Au composition and there is a clear tendency for surface segregation of the Ag atoms. Cluster stability is found to increase with increasing number of Au-Au and Ag-Au bonds and the segregation has been rationalised in terms of bonds strengths and elemental surface energies.

Global structure optimization study on Au 2-20

Abstract: The geometries and electronic properties of the most stable small Aun clusters with n=2 to 20 are presented. An intensive search for low-energy minima of Aun clusters was carried through using a density-functional tight-binding method combined with genetic algorithms for an unbiased global structure optimization. The structural and energetic properties of the small gold clusters are compared with those of planar Aun clusters with n=5 to 15.