Telecommunications—the state of the art

This article is a survey of the technological foundations of telecommunications, including both point-to-point electrical communication wing wires, cables and other guiding media. and radio wave broadcasting to many receivers via terrestrial transmitters or Earth-orbiting space satellites. The characteristics of analogue and digital telecommunication signals, the means available for their transmission and switching me described, together with the organization of local distribution, national and global networks. The various services that can be provided over such networks, including in addition to telephonic communication, audio and video conferencing, data and facsimile transmission and new vied-display data/information access services (Teletext) are outlined. Finally, the sociological implications of these technological and service developments me considered, for example in terms of their impact on urban and rural planning, where people live and work, and on energy economy by reducing the need to travel.     

Noisy teleportation of qubit states via the Greenberger-Horne-Zeilinger state or the W state

The effects of distributing entanglement through the amplitude damping channel or the phase damping channel on the teleportation of a single-qubit state via the Greenberger--Horne--Zeilinger state and the W state are discussed. It is found that the average fidelity of teleportation depends on the type and rate of the damping in the channel. For the one-qubit affected case, the Greenberger--Horne--Zeilinger state is as robust as the W state, i.e., the same quantum information is preserved through teleportation. For the two-qubit affected case, the W state is more robust when the entanglement is distributed via the amplitude damping channel; if the entanglement is distributed via the phase damping channel, the W state is more robust when the noisy parameter is small while the Greenberger--Horne--Zeilinger state becomes more robust when it is large. For the three-qubit affected case, the Greenberger--Horne--Zeilinger state is more robust than the W state.     

Is the 4.742 MeV state in 88Sr the 1− two-phonon state?

A nuclear resonance fluorescence experiment on ⁸⁸Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in ⁸⁸Sr, in contrast to the previous interpretation as a 1⁻ two-phonon (2⁺ ₁⊗ 3⁻ ₁) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1⁺ state at 3.486 MeV may be considered as the 1⁺ ₁ one-phonon state and the very strong 1⁺ ₁→ 0⁺ ₁ deexcitation as proton spin-flip 2p_1/2→ 2p_3/2 transition. Received: 3 November 1999     

Approaching the ground state of the kagomé antiferromagnet

Y0.5Ca0.5BaCo4O7 contains kagomé layers of Co ions, whose spins are strongly coupled, with a Curie-Weiss temperature of -2200 K. At low temperature, T=1.2 K, our diffuse neutron scattering study with polarization analysis reveals characteristic spin correlations close to a predicted two-dimensional coplanar ground state with staggered chirality. The absence of three-dimensional long-range antiferromagnetic order indicates negligible coupling between the kagomé layers. The scattering intensities are consistent with high spin S=3/2 states of Co2+ in the kagomé layers and low spin S=0 states for Co3+ ions on interlayer sites. Our observations agree with previous Monte Carlo simulations indicating a ground state of effectively short range, staggered chiral spin order.     

Similarity of the Fermi surface in the hidden order state and in the antiferromagnetic state of URu₂Si₂

Shubnikov-de Haas measurements of high quality URu2Si2 single crystals reveal two previously unobserved Fermi surface branches in the so-called hidden order phase. Therefore, about 55% of the enhanced mass is now detected. Under pressure in the antiferromagnetic state, the Shubnikov-de Haas frequencies for magnetic fields applied along the crystalline c axis show little change compared with the zero pressure data. This implies a similar Fermi surface in both the hidden order and antiferromagnetic states, which strongly suggests that the lattice doubling in the antiferromagnetic phase due to the ordering vector Q(AF)=(001) already occurs in the hidden order. These measurements provide a good test for existing or future theories of the hidden order parameter.     

Is the nucleon a bound state?

In this paper we deal with the question of whether or not the nucleon is a bound state. It is shown that previous work on this problem is not conclusive. We find, however, a simple criterion which allows for an experimental decision of this question. For the nucleon to be a bound state, thep _1/2,1/2 phase has to have a negative sign at the inelastic threshold. A positive phase excludes the bound state picture but allows ap _1/2,1/2 resonance to occur.     

Generation of GHZ state and cluster state with atomic ensembles via the dipole-blockade mechanism

This paper proposes scalable schemes to generate the Greenberger-Horne-Zeilinger (GHZ) state and the cluster state with atomic ensembles via the dipole blockade mechanism on an atom chip, where the qubit is not carried by a single atom but an atomic ensemble. In the protocols, multiqubit entangled states are determinately prepared. Needlessness for single-photon source further decreases the complexity of the experiment. Based on the present laboratory technique, the schemes may be realized. The achieved results reveal a prospect for large-scale quantum communication and quantum computation.     

Preparation of the W state via cavity QED

A scheme for preparation of the tripartite W state via cavity quantum electrodynamics is presented in this paper. And the scheme can be generalized to prepare the n-atom W states. The second part of this paper shows how to prepare n-cavity W states. All cavities involved are initially in the vacuum states, thus the requirement on the quality factor of the cavities is greatly loosened.     

Kaon electroproduction from the deuteron and the Λn final state interaction

Inclusive and exclusive cross sections are calculated for thed(e,eK ⁺)n reaction using amplitudes describing the elementary photo,p(,K ⁺), and electroproduction,p(e, eK ^–), processes. The sensitivity of the theoretical cross section to the final staten interaction is examined for severalN potentials. The utility of this reaction for investigating possible strange dibaryon resonances is discussed.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.The authors gratefully acknowledge Dr. Lacy Petris and Professor Ian Morrison for very beneficial interactions and assistance. This research was supported in part by the U.S. Derpatment of Energy and the Australian Research Grants Scheme. One of the authors (S.C.) also acknowledges the support and hospitality extended by the School of Physics, University of Melbourne during a short term visit.     

Cascade γ decay of the 191Os compound state

The intensities of two-step cascades to the final levels with excitation energies below 0.82 MeV have been determined from the accumulated experimental data on the γ-γ coincidences at thermal neutron capture into ¹⁹⁰Os. These intensities made it possible to establish the decay scheme for the compound nucleus to excitation energies of about 3 MeV. The intervals of the level densities and sums of radiative strength functions of the E1 and M1 transitions, which exactly reproduce the experimental cascade intensities, have been found from the total cascade intensities. The level density is approximated by the sum of the partial densities of levels for different numbers n of quasiparticles, with the coefficient of collective increase in the density, unambiguously determined by the accepted concepts about the energy dependence of the correlation functions of the nucleons of an excited nucleus.     

Equations of state in the Brans–Dicke cosmology

We investigate the Brans–Dicke (BD) theory with the potential as cosmological model to explain the present accelerating universe. In this work, we consider the BD field as a perfect fluid with the energy density and pressure in the Jordan frame. Introducing the power-law potential and the interaction with the cold dark matter, we obtain the phantom divide which is confirmed by the native and effective equation of state. Also we can describe the metric f(R) gravity with an appropriate potential, which shows a future crossing of the phantom divide in viable f(R) gravity models when employing the native and effective equations of state.     

Ground state features of the Fröhlich model

Following the ideas behind the Feynman approach, a variational wave function is proposed for the Fröhlich model. It is shown that it provides, for any value of the electron-phonon coupling constant, an estimate of the polaron ground state energy better than the Feynman method based on path integrals. The mean number of phonons, the average electronic kinetic and interaction energies, the ground state spectral weight and the electron-lattice correlation function are calculated and successfully compared with the best available results.Received: 2 July 2003, Published online: 19 November 2003PACS: 71.38.Fp Large or Fröhlich polarons     

The ground state of the Frenkel–Kontorova model

The continual approximation of the ground state of the discrete Frenkel–Kontorova model is tested using a symmetric algorithm of numerical simulation. A “kaleidoscope effect” is found, which means that the curves representing the dependences of the relative extension of an N-atom chain vary periodically with increasing N. Stairs of structural transitions for N ? 1 are analyzed by the channel selection method with the approximation N = ∞. Images of commensurable and incommensurable structures are constructed. The commensurable–incommensurable phase transitions are stepwise.     

Gamow-Teller β transition from the 2− ground state of88Rb to the 3− excited state of88Sr

The Gamow-Tellerβ-transition from the ground state 2^? of⁸⁸Rb to the 3^? level at 2.734 MeV of⁸⁸Sr is studied. The nuclear matrix element 〈σ〉 and the lofft value are calculated using complete nuclear wave functions for the initial and final states. It is shown that, contrary to the normal assumption, the component ¦π2p ₃ ^2/?1 π1g _9/2〉 of the final state does give a very important contribution to 〈σ〉 due to the presence of strong cancellation effects. Although our calculations favour a wave function for the 3^? level⁸⁸Sr where neutron 1h—1p configurations are not included, there are still some facts which make that our results cannot be taken as conclusive. Nuclear Structure⁸⁸Rb,⁸⁸Sr, calculated the Gamow-Teller nuclear matrix element 〈σ〉 and the logft value using a shell model.     

g-factors in the ground state and in the γ-bands in 160,162,164Dy

The g-factors of some members of the ground state band and of the 2⁺ state in the %-vibrational band have been measured in ^160,162,164Dy using the Coulomb Excitation Transient Field technique, induced by ⁵⁸Ni projectiles at 230, 210 and 217 MeV, respectively. The g-factors in the ground state band are consistent with a constant value, while that of the 2⁺_% states is about 20% larger in average than those in the ground state band. Results are discussed in the frame of the systematics in this nuclear region.     

Calculation of the fine structure of the level in Rydberg state of lithium

The level shift and level formula of lithium atom in Rydberg states are achieved by means of the calculation of polarization of the atomic core (including the contribution of dipole moment, quadrupole moment and octupole moment);meanwhile, the effect of relativity theory, the orbital angular momentum L and the spin angular momentum S coupling (LS coupling), and high order correction of the effective potential are considered. The some fine structures (N=5～12,L=4～9,J=L±1/2) and the corresponding level intervals in Rydberg states can be calculated by the above-mentioned level formula and compared with correlated experimental data.     

Calculation of the fine structure of the level in Rydberg state of lithium

The level shift and level formula of lithium atom in Rydberg states are achieved by means of the calculation of polarization of the atomic core （including the contribution of dipole moment, quadrupole moment and octupole moment） ; meanwhile, the effect of relativity theory, the orbital angular momentum L and the spin angular momentum S coupling （IS coupling）, and high order correction of the effective potential are considered. Thesome fine structures （N = 5- 12, L = 4-9, J = L ± 1/2） and the corresponding level intervals in Rydberg statescan be calculated by the above-mentioned level formula and compared with correlated experimental data.     

Measurement of the strong-interaction shift and broadening of the ground state of the pp̄ atom

The K_α X-rays from pp̄ atoms formed in H₂ gas at normal temperature and pressure are unambiguously identified by coincidences with L X-rays populating the 2P level. Background due to inner bremsstrahlung is suppressed by selecting events annihilating into neutral final states only. The K_α line is observed with a significance of more than 25 standard deviations at an energy of 8.67 (15) keV. From fits to the K_α line we obtain a strong-interaction shift and width of the 1S level, averaged over the unresolved spin singlet and triplet contributions, of ΔE + iΓ/2 = [−0.70(15) + i0.80(20)] keV.