This paper discusses methods for the optical teleportation of continuous-variable polarization states. We show that using two pairs of entangled beams, generated using four squeezed beams, perfect teleportation of optical polarization states can be performed. Restricting ourselves to three squeezed beams, we demonstrate that polarization state teleportation can still exceed the classical limit. The three-squeezer schemes involve either the use of quantum nondemolition measurement or biased entanglement generated from a single squeezed beam. We analyze the efficacies of these schemes in terms of fidelity, signal transfer coefficients, and quantum correlations.

The theory of long-range relativistic interactions in the Cowan-Griffin approximation is formulated and the expression for the leading-order relativistic correction to the dispersion energy is derived. It is shown that the relativistic dispersion energy for closed-shell atoms behaves as $C_6^{\mathrm{rel}}{R}^{-6}$ with the interatomic distance R. The relativistic correction to the van der Waals constant $\delta C_6$ is expressed as a Casimir-Polder integral of the product of a nonrelativistic frequency-dependent linear-response function with two dipole operators and a frequency-dependent quadratic-response function, including in addition one relativistic operator. In the Cowan-Griffin approximation, there are two contributions, involving the mass-velocity and the one-electron Darwin operators. The QED retardation effect on the long-range relativistic dispersion energy is also considered, and applications to the helium, calcium, and cadmium dimers are presented.

We have determined the anisotropy parameter $\beta$ for the electron angular distribution in direct $2p$ photoionization of free Mn and Cr atoms. By using a high-resolution electron spectrometer and by rotating the polarization axis of the linearly polarized synchrotron radiation the values for $\beta$ could be derived with high precision and separately for the different multiplet components. Combination of the experimental results with Hartree-Fock based single configuration and multiconfiguration ab initio calculations gives new insight into the atomic $3d$-metal $2p$ photoionization process. Configuration interaction in the final ionic states need to be taken into account to adequately describe the measured photoelectron angular distributions.

We report measurements of $\mathrm{}(4+2)\mathrm{}$ resonantly enhanced multiphoton ionization (REMPI) of CO. The excitation route is first to the $\nu =0\mathrm{}$ level of the CO $B{}^1{\Sigma }^{+}$ state followed by the absorption of additional two photons to reach the ionization continua. Measurements of the ${\mathrm{CO}}^{+}$ and ${\mathrm{C}}^{+}$ ion intensities as a function of the wavelength were made, yielding no rotational structure of any intermediate resonant state in contrast to the $\mathrm{}(2+1)\mathrm{}$ REMPI experiment. In a second measurement, the laser frequency was set at the $\upsilon =0\mathrm{}$ band head of the $B{}^1{\Sigma }^{+}$ and the kinetic-energy spectrum of the ejected electrons was measured. The observed photoelectron spectrum is assigned to the multiphoton ionization of CO via the resonant $X{}^1{\Sigma }^{+}$ to $B{}^1{\Sigma }^{+}$ excitation.

We present a scheme for rapidly loading a Bose-Einstein condensate into a single Bloch state of a weak optical lattice at a quasimomentum of $q=ħk.\mathrm{}$ Rabi cycling of the Bose-Einstein condensate between momentum states is modified by a phase shift applied to the lattice. By appropriately choosing the magnitude and timing of the phase shift, we demonstrate nearly perfect loading of the lattice ground state, the signature of which is an abrupt halt to the Rabi cycling.

We obtain exact expressions for the Casimir forces between arbitrary materials using the concept of surface impedance. We verify their consistency with the well-known expressions for perfect conductors and with Lifshitz formula for semi-infinite local homogeneous media. As an application we present a full and rigorous calculation of the Casimir force between two metallic half spaces described by a hydrodynamic nonlocal dielectric response.

We measured the charge transfer rate coefficients for the reactions ${\mathrm{S}}^{2+}+{\mathrm{H}}_2\to \mathrm{products},$ ${\mathrm{S}}^{2+}+{\mathrm{N}}_2\to \mathrm{products},$ and ${\mathrm{S}}^{2+}+\mathrm{CO}\to \mathrm{products}$ using a radio frequency trap. ${\mathrm{S}}^{2+}$ ions are produced by laser ablation of a solid tungsten disulfide target. We derive the rate coefficient of the reaction from the decay rate of the stored ions in the trap. The rate coefficients for the above three reactions are $1.58\left(0.13\right)\mathrm{}\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $T_{\mathrm{equiv}}=1077\mathrm{}\mathrm{K},$ and $1.67\left(0.12\right)\mathrm{}\times {10}^{-9}$ and $1.78\left(0.13\right)\mathrm{}\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $T_{\mathrm{equiv}}=6462\mathrm{}\mathrm{K}.$

We measured the total charge-transfer rate coefficients for ${\mathrm{C}}^{2+}$ with ${\mathrm{H}}_2,$ ${\mathrm{N}}_2,$ and CO using a cylindrical radiofrequency ion trap. ${\mathrm{C}}^{2+}$ ions were produced by the electron impact of residual CO in an ultrahigh-vacuum chamber. The rate coefficients for ${\mathrm{C}}^{2+}$ with ${\mathrm{H}}_2,$ ${\mathrm{N}}_2,$ and CO are measured to be $8.77\mathrm{}\left(0.71\right)\mathrm{}\times {10}^{-11}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ ${(T}_{\mathrm{equiv}}=2.63\mathrm{}\times {10}^3\mathrm{K}),$ $1.08\mathrm{}\left(0.07\right)\mathrm{}\times {10}^{-10}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ ${(T}_{\mathrm{equiv}}=1.17\mathrm{}\times {10}^4\mathrm{K}),$ and $4.58\mathrm{}\left(0.29\right)\mathrm{}\times {10}^{-10}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ ${(T}_{\mathrm{equiv}}=1.17\mathrm{}\times {10}^4\mathrm{K}).\mathrm{}$ The rate coefficient for ${\mathrm{C}}^{2+}$ with He is estimated to be less than ${10}^{-12}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ ${(T}_{\mathrm{equiv}}=4.38\mathrm{}\times {10}^3\mathrm{K}).\mathrm{}$

Levinson theorem for a charged particle moving in an arbitrary short-range potential and the field of the Aharonov-Bohm magnetic flux is established. The theorem constructs the relation ${\delta }_{\alpha }{\mathrm{}\left(0\right)=n}_{\alpha }\pi$ between the phase shift ${\delta }_{\alpha }\mathrm{}\left(k\right)\mathrm{}$ of scattering state at zero momentum and the total number $n_{\alpha }$ of bound states for the αth angular-momentum channel, where $\alpha =|m+{\mu }_0|$ is a real number $(m=\mathrm{integer},$ and ${\mu }_0=-\Phi /{\Phi }_0$ with $\Phi$ being the magnetic flux and ${\Phi }_0=hc/e$ the fundamental flux quantum). The relation means that the phase shift at the threshold of zero momentum can serve as a counter for the bound states in the general angular-momentum channel.

We investigate the electromagnetic transition probabilities for the helium atom embedded in a superstrong magnetic field taking into account the finite nuclear mass. We address the regime $\gamma =100\mathrm{}–10000\mathrm{a}.\mathrm{u}.\mathrm{}$ studying several excited states for each symmetry, i.e., for the magnetic quantum numbers $0,-1,-2,-3,$ positive and negative z parity, and singlet and triplet symmetry. The oscillator strengths as a function of the magnetic field and, in particular, the influence of the finite nuclear mass on the oscillator strengths are shown and analyzed.

We discuss level schemes of small quantum-dot turnstiles and their applicability in the production of entanglement in two-photon emission. Due to the large energy splitting of the single-electron levels, only one single-electron level and one single-hole level can be made resonant with the levels in the conduction band and valence band. This results in a model with nine distinct levels, which are split by the Coulomb interactions. We show that the optical selection rules are different for flat and tall cylindrically symmetric dots, and how this affects the quality of the entanglement generated in the decay of the biexciton state. The effect of charge-carrier tunneling and of a resonant cavity is included in the model.

A Keldysh-type theory of above-threshold detachment of electrons from negative ions is developed that includes the rescattering of the detached electron on the parent atom. The rescattering potential is the sum of the polarization potential and the static potential. The low-energy part of the spectra obtained reproduces the earlier results of Gribakin and Kuchiev. It is strongly dependent on the parity of the ground state, in contrast to the rescattering-induced high-energy part, whose shape is almost independent of the ground state as well as the rescattering potential. However, its height strongly depends on the latter, that is, on the respective ion (or atom). We relate our results to the recent experiment on photodetachment of ${\mathrm{F}}^{-}$ [I. Yu. Kiyan and H. Helm, Phys. Rev. Lett. 90, 183001 (2003)].

We show that, although the efficiency of a multiwave mixing process can be significantly enhanced by an ultra-slowly-propagating pump wave, a three-photon destructive interference between the generated wave and the pump wave limits the final achievable conversion efficiency.

Dissipation and decoherence, and the evolution from pure to mixed states in quantum physics, are handled through master equations for the density matrix. Master equations such as the Lindblad equation preserve the trace of this matrix. Viewing them as first-order time-dependent operator equations for the elements of the density matrix, a unitary integration procedure can be adapted to solve for these elements. A simple model for decoherence preserves the Hermiticity of the density matrix. A single, classical Riccati equation is the only one requiring numerical handling to obtain a full solution of the quantum evolution. The procedure is general, valid for any number of levels, but is illustrated here for a three-level system with two driving fields. For various choices of the initial state, we study the evolution of the system as a function of the amplitudes, relative frequencies, and phases of the driven fields and of the strength of the decoherence. The monotonic growth of the entropy is followed as the system evolves from a pure to a mixed state. An example is provided by the $n=3\mathrm{}$ states of the hydrogen atom in a time-dependent electric field, such degenerate manifolds affording an analytical solution.

The dynamics of entanglement is investigated on the basis of exactly solvable models of multiple quantum (MQ) NMR spin dynamics. It is shown that the time evolution of MQ coherences of systems of coupled nuclear spins in solids is directly connected with dynamics of the quantum entanglement. We studied analytically the dynamics of entangled states for two- and three-spin systems coupled by the dipole-dipole interaction. In this case the dynamics of the quantum entanglement is uniquely determined by the time evolution of MQ coherences of the second order. The real part of the density matrix describing MQ dynamics in solids is responsible for MQ coherences of the zeroth order while its imaginary part is responsible for the second order. Thus, one can conclude that the dynamics of the entanglement is connected with transitions from the real part of the density matrix to the imaginary one, and vice versa. A pure state which generalizes the Greenberger-Horne-Zeilinger (GHZ) and W states is found. Different measures of the entanglement of this state are analyzed for tripartite systems.

This work shows how two parties A and B can securely share unlimited sequences of random bits at optical speeds. A and B possess true-random physical sources and exchange random bits by using a random sequence received to cipher the following one to be sent. A starting shared secret key is used and the method can be described as a one-time-pad unlimited extender. It is demonstrated that the minimum probability of error in signal determination by the eavesdropper can be set arbitrarily close to the pure guessing level. Being based on the M-ry encryption protocol this method also allows for optical amplification without security degradation, offering practical advantages over the Bennett-Brassard 1984 protocol for key distribution.

Electronic excited states are computed through a technique for extracting them from a knowledge of the ground-state two-particle reduced density matrix (2-RDM). Diagonalization of the Hamiltonian in the basis set of one-particle excitations, deexcitations, and projections from the ground-state wave function yields those excited states dominated by one-particle excitations; however, explicit evaluation of the Hamiltonian requires a knowledge of the ground-state 4-RDM. Two techniques are developed for evaluating the Hamiltonian elements with only a knowledge of the 2-RDM: (i) the cumulant method in which the higher RDMs are reconstructed from the 2-RDM via cumulant theory and (ii) the Hermitian or anti-Hermitian operator method in which the higher RDMs are eliminated by selecting the basis functions to be Hermitian or anti-Hermitian. These techniques are extendable to the diagonalization of the Hamiltonian in basis sets of m-excitations where $m>\mathrm{}1.\mathrm{}$ Excited-state energies with an accuracy between 0.1% and 0.001% of their absolute values are determined in illustrative calculations on Be, LiH, ${\mathrm{H}}_2\mathrm{O},$ and BH.

Recent results for proton-argon total ionization cross sections [Kirchner et al. Phys. Rev. Lett. 79, 1658 (1997)] show large disagreement between theory and experiment for energies below 80 keV. To address this problem we have employed a recently developed theoretical method with a more pragmatic approach to the charge screening both in the initial and final channels. The target is considered as a one-electron atom and the interactions between this active electron and remaining target electrons are treated by a model potential including both short- and long-range effects. In the final channel the usual product of two continuum distorted wave functions each associated with a distinct electron-nucleus interaction is used. New results in the present calculation show good agreement in total cross sections for the energy range 10–300 keV with the measurement of Rudd et al. [Rev. Mod. Phys. 57, 965 (1985)].