Level scheme of <Superscript>242</Superscript>Am

Published level scheme of ²⁴²Am includes 39 levels, places 118 transitions out of 246 transitions measured, and has normalized χ² = 6.6, with the individual contribution to the total χ² of each of the 16 transitions with the worst energy placement being > 9. Using the program of construction of the level scheme with the aid of Ritz combinations enabled us to add 35 new levels, place 201 transitions, and construct the final level scheme with χ² = 1.3. No transition energy error in the final scheme differs from the error of the energy difference of levels between which this transition is placed by more than a factor of 3. Published in Russian in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 8, pp. 1225–1232. In memory of Yu. Akovali The article was translated by the author.     

Remote Preparation of a Two-Particle Entangled State via Two Tripartite <Emphasis Type="Italic">W</Emphasis> Entangled States

We present a scheme for remotely preparing a general two-particle entangled state via two tripartite W entangled states of different amplitudes. In this scheme one sender and two remote receivers are involved. The sender can help either one of the receivers to remotely reconstruct the original state with the aid of the other receiver’s two single-particle orthogonal measurements. It is shown that by means of the method of the positive operator-valued measurement, our remote state preparation scheme can be achieved probabilistically. This project supported by the National Key Basic Research and Development Program of China under Grant No. 2006CB921604 and the National Natural Science Foundation of China under Grant Nos. 60578050 and 10434060.     

Numerical stability of 2<Superscript>nd</Superscript> order Runge-Kutta integration algorithms for use in particle-in-cell codes

An essential ingredient of particle-in-cell (PIC) codes is a numerically accurate and stable integration scheme for the particle equations of motion. Such a scheme is the well known time-centered leapfrog (LF) method [1] accurate to 2^nd order with respect to the timestep Δt. However, this scheme can only be used forces independent of velocity unless a simple enough implicit implementation is possible. The LF scheme is therefore inapplicable in Monte-Carlo treatments of particle collisions [2] and/or interactions with radio-frequency fields [3]. We examine here the suitability of the 2^nd order Runge-Kutta (RK) method. We find that the basic RK scheme is nummerically unstable, but that conditional stability can be attained by an implementation which preserves phase space area. Examples are presented to illustrate the performance of the RK schemes. We compare analytic and computed electron orbits in a traveling nonlinear wave and also show self-consistent PIC simulations describing plasma flow in the vicinity of a lower hybrid antenna.     

Probabilistic Teleportation of an Arbitrary Two-mode <Emphasis Type="Italic">N</Emphasis>-photon Entangled State in Cavity QED

We propose a scheme for teleportation of an arbitrary two-mode N-photon entangled states in cavity QED. The scheme is based on the resonant interaction between Λ-type atoms and two-mode cavity fields. In contrast to all the theoretical schemes proposed previously in cavity QED for teleportation of two-mode cavity field states, in the present scheme, the established entanglement for the quantum channel is the type of the multi-dimensional entanglement between the symmetric multi-atom Dicke states and two-mode N-photon states. Therefore, the scheme extends the scope of the theoretical study of the teleportation.     

Long-distance quantum communication with “polarization” maximally entangled states

We propose a scheme for long-distance quantum communication where the elementary entanglement is generated through two-photon interference and quantum swapping is performed through one-photon interference. Local “polarization” maximally entangled states of atomic ensembles are generated by absorbing a single photon from on-demand single-photon sources. This scheme is robust against phase fluctuations in the quantum channels, moreover speeds up long-distance high-fidelity entanglement generation rate.     

Time and Energy Characteristics of Radiation at <Emphasis Type="Italic">Q</Emphasis>-switched Self-Frequency Conversion

The results of a theoretical study of quasi-phase matched processes at self-frequency conversion in the Q-switched regime are presented. A scheme containing a periodically poled active nonlinear crystal and an acousto-optical modulator inserted inside the cavity is considered. Solutions of the set of equations describing such scheme are obtained by numerical methods. The time dynamics of the self-frequency doubling, self-frequency summing, and self-parametric frequency conversion processes are studied in detail. The energy characteristics of the radiation are also calculated and compared with those in the stationary regime.     

Simultaneous Implementation of <Emphasis Type="Italic">Ni</Emphasis>SWAP and <Emphasis Type="Italic">NS</Emphasis>WAP Gates Using <Emphasis Type="Italic">N</Emphasis> + 1 Qubits in a Cavity or Coupled to a Circuit

We propose an effective method to realize NiSWAP and NSWAP gates in a cavity or coupled to a circuit driven by a strong microwave field. The scheme is insensitive to the initial state of the resonator mode, and the operation time is independent of the number of qubits involved in the gates operations. These logic gates can be realized in a time much shorter than the radiative time and the lifetime of the cavity photon, and can be realized in a time (nanosecond-scale) much smaller than the decoherence time and the dephasing time (microsecond-scale) in circuit QED. Numerical simulation under the influence of the gates operations shows that the scheme can be implemented with high fidelity. We also propose a detailed procedure and experimentally analyze its feasibility. Moreover, the scheme might be experimentally achieved efficiently within current state-of-the-art technology.     

Scheme for Concentration of the <Emphasis Type="Italic">W</Emphasis> Class State via Cavity Decay

We propose a concentration scheme of the W class state via cavity QED technique. In our scheme the influences of cavity decay and atomic spontaneous emission have been considered. Furthermore, the atomic spontaneous emission has been suppressed by using non-radiative transitions in atoms with three-level structure, and the photonic qubit is used as flying qubit and atomic qubit as stationary qubit. Therefore our scheme is comparatively easy to realize within techniques presently available.     

Effect of magnetic field on AF correlations in UPt<Subscript>3</Subscript>

Following our recent suggestion that antiferrmagnetism of UPt₃ can be understood within the crystal field splitting scheme and that the observed below 5 K AF correlations are dominated by thermal fluctuations, we examine here the effect of a uniform magnetic field on these correlations. Orientations of field in the basal plane and perpendicular to it are considered. The field of a few teslas must have a pronounced effect which can be used as a check of the suggested scheme.     

High-contrast dark resonance on the D<Subscript>2</Subscript>-line of <Superscript>87</Superscript>Rb in a vapor cell with different directions of the pump-probe waves

We propose a novel method enabling to create a high-contrast dark resonance in the ⁸⁷Rb vapor D₂-line. The method is based on an optical pumping of atoms into the working states by a two-frequency, linearly-polarized laser radiation propagating perpendicularly to the probe field. This new scheme is compared to the traditional scheme involving the σ⁺-polarized probe beam only, and significant improvement of the dark resonance parameters is found. Qualitative considerations are confirmed by numerical calculations.     

Precise determination of the neutron scattering length of lead isotopes <Superscript>204</Superscript>Pb, <Superscript>207</Superscript>Pb and <Superscript>208</Superscript>Pb by neutron interferometry

Excited states of ⁶⁸Ga have been investigated through the ⁵⁵Mn(¹⁶O, 2pn) reaction at projectile energy 55 MeV. The level scheme has been extended up to 7.8 MeV. Altogether six new excited levels could be identified and twelve previously unobserved γ-transitions have been placed in the modified level scheme. Received: 19 June 2000 / Accepted: 20 October 2000     

Isospin dependence of electric-transition probabilities <Emphasis Type="Italic">B</Emphasis>(E2) in the unitary scheme

In a physical basis of the unitary scheme, analytic formulas for the probabilities B(E2κL → κ′L′) and their isospin factors for the (λ0) and (λ2) representations of the SU(3) group were obtained for even-even nuclei. It was shown that the isospin correction must be taken into account at low L and in the case of off-diagonal transitions in κ. The results obtained in the unitary scheme are compared with the results of other models and with experimental data. At high L, the transition probabilities B(E2κL → κ′L′) are markedly smaller in the unitary scheme than in the rotational model, while, for L ≪ λ, these probabilities in the unitary scheme and in the rotational model are close.     

Complete <Emphasis Type="Italic">N</Emphasis>-Photon Greenberger-Horne-Zeilinger State Analysis Using Hyperentanglement

We present a scheme for N-photon Greenberger-Horne-Zeilinger (GHZ) state analysis using hyperentanglement in polarization and time-bin degrees of freedom. The scheme only needs linear optics elements and single-photon detectors, which is feasible with current technology. The set of 2 ^N mutual orthogonal states can be unambiguously distinguished and the protocol is expected to find useful applications in quantum information processing.     

Kinetic Flux–Vector Splitting for the Navier–Stokes Equations

Before a hybrid scheme can be developed combining the direct simulation Monte Carlo (DSMC) method and a Navier–Stokes (NS) representation, one must have access to compatible kinetic-split fluxes from the NS portion of the hybrid scheme. The kinetic theory basis is given for the development of the required fluxes from the Chapman–Enskog velocity distribution function for a simple gas; and these are then extended to a polyatomic gas by use of the Eucken approximation. The derived fluxes are then used to implement boundary conditions at solid surfaces that are based on concepts associated with kinetic theory and the DSMC method. This approach is shown to lead to temperature slip and velocity slip as a natural outcome of the new formulation, a requirement for use in the near-continuum regime where DSMC and NS must be joined. Several different flows, for which solid boundaries are not present, are computed using the derived fluxes, together with a second-order finite-volume scheme, and the results are shown to agree well with several established numerical schemes for the NS equations.     

Possibility of X‐ray pulse compression using an asymmetric or inclined double‐crystal monochromator

It is shown theoretically that the asymmetric or inclined double‐crystal X‐ray monochromator may be used for X‐ray pulse compression if the pulse is properly chirped. By adjusting the mutual distance of the two asymmetric or inclined crystals it should be possible to achieve even a sub‐femtosecond compression of a chirped free‐electron laser pulse. The small d‐spacing of the crystal enables a more compact scheme compared with the currently used grating compression scheme. The asymmetric cut of the crystal enables the acceptance of a larger bandwidth. The inclined cut has larger tunability.     

Self‐Force in 1D Electrostatic Particle‐in‐Cell Codes for NonEquidistant Grids

Effects of non‐equidistant grids on momentum conservation is studied for simple test cases of an electrostatic 1D PIC code. The aim is to reduce the errors in energy and momentum conservation. Assuming an exact Poisson solver only numerical errors for the particle mover are analysed. For the standard electric field calculation using a central‐difference scheme, artificial electric fields at the particle position are generated in the case when the particle is situated next to a cell size change. This is sufficient to destroy momentum conservation. A modified electric field calculation scheme is derived to reduce this error. Independent of the calculation scheme additional fake forces in a two‐particle system are found which result in an error in the total kinetic energy of the system. This contribution is shown to be negligible for many particle systems. To test the accuracy of the two electric field calculation schemes numerical tests are done to compare with an equidistant grid set‐up. All tests show an improved momentum conservation and total kinetic energy for the modified calculation scheme of the electric field. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coherent population trapping resonance on the <Superscript>87</Superscript>Rb D<Subscript>1</Subscript> line in the field of circularly polarized counterpropagating waves

The study of the previously proposed method for improving the parameters of the coherent population trapping resonance on the ⁸⁷Rb D₁ line using two counterpropagating bichromatic fields with orthogonal circular polarizations is continued. The method consists in elimination of trap states existing in the conventional σ⁺ measurement scheme and limiting the resonance amplitude. The resonance parameters are studied in a wide range of pump radiation intensities and in various configurations implementing the σ⁺-σ^? scheme.     

Efficient Symmetric Five-Party Quantum State Sharing of an Arbitrary <Emphasis Type="Italic">m</Emphasis>-Qubit State

We present an efficient symmetric scheme for five-party quantum state sharing of an arbitrary m-qubit state with 2m three-particle entangled states. The implementations of this scheme only need to exploit the CNOT gate operations and the single-particle measurements, instead of the three-particle GHZ-state measurements, which makes it more convenient in a practical application than some previous schemes. In addition, its total efficiency can approach the maximal value in theory.     

A three-step laser stabilization scheme for excitation to Rydberg levels in <Superscript>85</Superscript>Rb

We demonstrate a three-step laser stabilization scheme for excitation to nP and nF Rydberg states in ⁸⁵Rb, with all three lasers stabilized using active feedback to independent Rb vapor cells. The setup allows stabilization to the Rydberg states 36P_3/2–70P_3/2 and 33F_7/2–90F_7/2, with the only limiting factor being the available third step laser power. We study the scheme by monitoring the three laser frequencies simultaneously against a self-referenced optical frequency comb. The third step laser, locked to the Rydberg transition, displays an Allan deviation of 30 kHz over 1 second and <80 kHz over 1 hour. The scheme is very robust and affordable, and it would be ideal for carrying out a range of quantum information experiments.     

On the unique possibility of significantly increasing the contrast of dark resonances on the D1 line of <Superscript>87</Superscript>Rb

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for the D1 line of alkali atoms with nuclear spin I = 3/2 by bichromatic linearly polarized light (lin‖lin field) under the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for the D1 line of ⁸⁷Rb.