We propose a realizable experimental scheme to prepare superposition of the vacuum and one-photon states by truncating an input coherent state. The scheme is based on the quantum scissors device proposed by Pegg, Phillips, and Barnett [Phys. Rev. Lett. 81, 1604 (1998)] and uses photon-counting detectors, a single photon source, and linear optical elements. Realistic features of the photon counting and single-photon generation are taken into account and possible error sources are discussed together with their effect on the fidelity and efficiency of the truncation process. Wigner function and phase distribution of the generated states are given and discussed for the evaluation of the proposed scheme.

It is shown that broadband optical continua may be generated as light propagates through a coherently prepared medium. Stimulated Raman scattering is a parametric process responsible for the spectral broadening. Even though the generation of spectral components is limited by the dispersion of the medium, numerical estimates for realistic parameters show feasibility of generating coherent optical continua with total bandwidth of several hundred terahertz without implementation of any dispersion compensating technique. Finally, a technique for producing broadband coherent optical spectra and, thus, ultrashort pulses of radiation is proposed.

The energies of an electron above a liquid-helium surface are analyzed in terms of an electron-atom polarizability potential with an infinite barrier. An integration over a layer, and a summation over different layers, leads to a one-dimensional Coulomb potential with a ${1/x}^2$ correction. This potential provides an accurate description of the observed one-dimensional Rydberg energies with a quantum defect.

We have studied the multiple ionization of Xe with intense laser pulses. For the highest intensities, and, concomitantly, the highest ionic charge states, there is only evidence of sequential and not of simultaneous multiple ionization. The multiple-ionization rate below saturation is greatly reduced, compared to the theoretical predictions based on nonrelativistic multiple-ionization models. Since simultaneous multiple ionization requires the return of the first ionized electron to its parent atom, our results show suppression of this return. This suppression is expected to occur due to the relativistic photon momentum imparted by the laser field, as seen in simulations of relativistic classical trajectories.

We show that the Eckhaus instability induced by spatial nonuniformities, observed in hydrodynamics, can also destabilize optical systems. On the example of a one-dimensional parametric system (a modulated multimode laser), we show numerically that the nonuniformities select a wave number outside the Eckhaus-stable band, leading to periodic or irregular phase slips. The instability is confirmed experimentally by using a modulated fiber laser.

We present a general analysis of the role of initial correlations between the open system and an environment on quantum dynamics of the open system.

We derive an extremal equation for an optimal completely positive map, which most closely approximates a given transformation between pure quantum states. Moreover, we also obtain an upper bound on the maximal mean fidelity that can be attained by the optimal approximate transformation. The developed formalism is applied to a universal-NOT gate, quantum cloning machines, quantum entanglers, and a qubit ϑ shifter.

It has previously been shown that probabilistic quantum logic operations may be performed using linear optical elements, additional photons (ancilla), and post-selection based on the output of single-photon detectors. Here we describe the operation of several quantum logic operations of an elementary nature, including a quantum parity check and a quantum encoder, and we show how they may be combined to implement a controlled-NOT (CNOT) gate. All of these gates may be constructed using polarizing beam splitters that completely transmit one state of polarization and totally reflect the orthogonal state of polarization, which allows a simple explanation of each operation. We also describe a polarizing beam splitter implementation of a CNOT gate that is closely analogous to the quantum teleportation technique previously suggested by Gottesman and Chuang [Nature 402, 390 (1999)]. Finally, our approach has the interesting feature that it makes practical use of a quantum-eraser technique.

We present a teleportation protocol based upon the entanglement produced from Fock states incident onto a beam splitter of arbitrary transmissivity. The teleportation fidelity is analyzed, its trends being explained from consideration of a beam splitter’s input-output characteristics.

It is known in density-functional theory that the noninteracting kinetic-energy density functional $T_s\left[\rho \right]$ is not first-degree homogeneous in density scaling. However, it is shown here that, for every particle number N, there is an N-particle noninteracting kinetic-energy density functional $T_N\left[\rho \right],$ that is, a density functional that gives the noninteracting kinetic energy for N-particle densities, which is of first-degree homogeneity in the density $\rho \left(\stackrel{\rightharpoonup }{r}\right).\mathrm{}$ This gives a powerful tool, a strong requirement, for constructing such functionals. A systematic procedure to obtain the real part of $T_N\left[\rho \right],$ the full $T_N\left[\rho \right]$ in one-dimension, for each N is also proposed. It is pointed out, further, that in the Euler-Lagrange equations that determine the one-particle orbitals that define $T_s\left[\rho \right],$ the Lagrange multiplier that forces the orbitals to yield $\rho \left(\stackrel{\rightharpoonup }{r}\right)$ is not other than the first derivative of $T_s\left[\rho \right],$ $\delta T_s\left[\rho \right]/\delta \rho \left(\stackrel{\rightharpoonup }{r}\right),$ which yields a natural derivation of the Kohn-Sham equations. Utilizing the same idea, it is shown for ground states how the Schrödinger equation can be derived from the basics of density-functional theory as well.

The atomic mass of ${}^6\mathrm{Li}$ has been measured using a Penning-ion-trap mass spectrometer to be 6.015 122 795(16) u. The fractional measurement uncertainty of $\pm 2.7\times {10}^{-9}$ represents a 30-fold improvement over that of the accepted published value. External ion sources were used to create ions outside the cryogenic (4 K) environment of the Penning trap and an ion-transport beamline was used to deliver ions into the trap for measurement. The ion mass ratios of ${}^6{\mathrm{Li}}^{+}{:}^{12}{\mathrm{C}}^{2+}$ and ${}^6{\mathrm{Li}}^{+}:{\mathrm{D}}_3^{+}$ were measured using this apparatus and the atomic mass of neutral ${}^6\mathrm{Li}$ was derived from these ratios. A measurement of the ${\mathrm{He}}^{+}{:\mathrm{D}}_2^{+}$ mass ratio with a fractional uncertainty of $\pm 1.1\times {10}^{-9}$ and differing from the accepted published value by a fractional amount $-0.6\times {10}^{-9}$ is also reported.

We measured ejected electron spectra caused by autoionization of doubly excited states in He atoms; the excited He was made by double electron capture of low-energy ${\mathrm{He}}^{2+}$ ions colliding with Ba atoms. Measurements were performed by means of zero degree electron spectroscopy at projectile energies from 40 to 20 keV. Electron spectra due to autoionization from the states $\mathrm{He}{(2\mathrm{lnl}}^{\prime })$ to ${\mathrm{He}}^{+}\mathrm{}\left(1s\right)\mathrm{}$ for $n>~2,$ and those from $\mathrm{H}\mathrm{e}\left(3\mathrm{}{\mathrm{lnl}}^{\prime }\right)$ to ${\mathrm{He}}^{+}$ $(2s$ or $2p)$ for $n>~3,$ were observed. Line peaks in the spectra were identified by comparing observed electron spectra with those of several theoretical calculations. It was found that doubly excited states of relatively high angular momenta such as the D and F terms were conspicuously created in a quite different manner from the cases of the production of doubly excited states by the use of photon, electron, or ion impacts on neutral He atoms. Rydberg states with large n values were observed with high population in both the $\mathrm{He}{(2\mathrm{lnl}}^{\prime })$ and $\mathrm{He}{(3\mathrm{lnl}}^{\prime })$ series. Other remarkable features in the electron spectra are described and the mechanisms for the production of these electron spectra are discussed qualitatively.

K- and L-shell ionization induced by 20 MeV/u He, C, O, and Ne beams on Ta, Pb, and Th targets, and 80 MeV/u He, C, O beams on a Pb target has been studied. K x-ray production cross sections have been measured and compared with theoretical calculations. Probabilities of creation of one additional L-shell hole, accompanying a K-shell hole, have been deduced from experimental data, using the theoretical positions and intensities of the diagram and satellite K x-ray lines, obtained from the multiconfiguration Dirac-Fock calculations. This approach avoids explicit measurements of the L x-rays and can be applied with the use of a standard Ge detector.

Relativistic single-differential and total cross sections of positron-impact ionization for ions in the helium isoelectronic sequence: He, ${\mathrm{Li}}^{+},$ ${\mathrm{C}}^{4+},$ ${\mathrm{Na}}^{9+},$ ${\mathrm{Fe}}^{24+},$ and ${\mathrm{Ag}}^{45+},$ are calculated in the two-potential distorted-wave approximation. Two models are used to account for the mutual screening of the scattered positron and the ejected electron. Results are compared with available theoretical and experimental data. The systematics of ionization cross sections along the isoelectronic sequence is also studied.

We study theoretically Doppler laser cooling of a cluster of two-level atoms confined in a linear ion trap. Using several consecutive steps of averaging we derive, from the full quantum-mechanical master equation, an equation for the total mechanical energy of a one-dimensional crystal, defined on a coarse-grained energy scale whose grid size is smaller than the linewidth of the electronic transition. This equation describes the cooling dynamics for an arbitrary number of ions in the quantum regime. We discuss the validity of the ergodic assumption (i.e., that the phase-space distribution is only a function of energy). From our equation we derive the semiclassical limit (i.e., when the mechanical motion can be treated classically) and the Lamb-Dicke limit (i.e., when the size of the mechanical wave function is much smaller than the laser wavelength). We find a Fokker-Planck equation for the total mechanical energy of the system, whose solution is in agreement with previous analytical calculations that were based on different assumptions and valid only in their specific regimes. Finally, in the classical limit we derive an analytic expression for the average coupling, by light scattering, between motional states at different energies.

We report the observation of multiple bifurcations in a nonlinear Hamiltionian system: laser-cooled atoms in a standing wave with single-frequency intensity modulation. We provide clear evidence of the occurrence of bifurcations by analyzing the atomic momentum distributions.

Momentum correlations in a one-dimensional equilibrium ensemble of trapped fermions, with a point interaction between particles of opposite spin have been studied. In the degenerate regime correlations were observed between fermions with opposite spins and momenta, similar to Cooper pairing. These correlations appear as soon as the temperature is below the Fermi energy, which is a much less stringent condition than that of the BCS transition proper. Calculations are carried out in both perturbative and non-perturbative regimes. To achieve the latter, it is shown that interacting fermionic dynamics may be solved as a stochastic linear transformation of Grassmann algebra generators, much in the way random c-number paths are introduced in the conventional quantum stochastics of bosons. Importantly, the method thus emerging is inherently free of the sign problem.

A method is considered for lowering the temperature of neutral atoms, based on the gaining of information on the translational state of individual atoms and using this information to separate slow and fast atoms. The minimum attainable temperature of the atomic ensemble is substantially lower than the temperature corresponding to the recoil energy of the atoms.

Multifrequency light can be exploited to produce different forms of optical forces on atoms. Here, we demonstrate that weakly modulated light can produce forces stronger than the radiative force limit $ħk\gamma /2\mathrm{}$ that can be used either for cooling or for deflection. We present various models of these forces and compare them with our measurements.

Giant dipole states of singly and excited doubly multielectron atoms in crossed electric and magnetic fields are investigated. A gauge-independent approach to the pseudoseparation of the center of mass yields a generalized multielectron potential in crossed fields that serves as a basis for the study of the dipole states. For doubly excited systems, a class of highly symmetric decentered configurations is found and the properties of the corresponding resonances are determined. An outline on multiply excited systems is given.