Field ionization measurements of ${\mathrm{CH}}_3\mathrm{I}$ and ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{I}$ dopant high-$n$ molecular Rydberg states in argon and krypton perturbers are presented as a function of perturber number density along various isotherms up to the density of the triple point liquid. Using these data, a new local Wigner-Seitz model for the density-dependent energy $V_0\left({\rho }_{\mathrm{P}}\right)$ of a quasifree electron in argon and krypton is developed. This model, which contains only one adjustable parameter, uses a local Wigner-Seitz radius derived from the local number density rather than from the bulk number density, includes a statistical mechanical calculation of both the ion/medium polarization energy and the electron/medium polarization energy, and includes the thermal kinetic energy of the quasifree electron. Using this model, $V_0\left({\rho }_{\mathrm{P}}\right)$ and the perturber-induced energy shift of the dopant ionization potential ${\Delta }_{\mathrm{D}}\left({\rho }_{\mathrm{P}}\right)$ are calculated to within $\pm 0.1\%$ of experiment. Previously reported $V_0\left({\rho }_{\mathrm{P}}\right)$ data for xenon are also shown to be interpretable within this new model.

Dramatic examples of the importance of nondipole effects in photoelectron angular distributions at photon energies as low as a few tens of eV are found. This occurs in $3p$ photoionization of the $\mathrm{Ca}\left(4s^2\right)$ atom and its ions ${\mathrm{Ca}}^{+}\left(4s^1\right)$ and ${\mathrm{Ca}}^{2+}\left(4s^0\right)$ at photon energies corresponding to a quadrupole $3s\to 3d$ resonance. The nondipole parameters are found to drastically increase to as much as 65% of the dipole counterpart. The quintessence is that this resonance turns out to be giant because of selective orbital collapse for the quadrupally excited $3d$ orbital. In addition, nondipole effects are known to result in an electric current—the drag current—in a gaseous medium upon photoionization of its atoms. We present our calculated data for the drag current in Ca vapor as well, in an attempt to trigger experimental studies of this interesting phenomenon in general. Calculations were performed within the framework of the random-phase approximation with exchange.

We present numerical calculations of the time-frequency characteristics of cutoff harmonics generated by few-cycle laser pulses. We find that for driving pulses as short as three optical cycles, the adiabatic prediction for the harmonic chirp rate is very accurate. This negative chirp is so large that the resulting bandwidth causes substantial overlap between neighboring harmonics, and the harmonic phase therefore appears to not vary in time or frequency. By adding a compensating positive chirp to the driving pulse, which reduces the harmonic bandwidth and allows for the appearance of the negative chirp, we can measure the harmonic chirp rates. We also find that the positive chirp on the driving pulse causes the harmonics to shift down in frequency. We show that this counterintuitive result is caused by the change in the strong field continuum dynamics introduced by the variation of the driving frequency with time.

A theory of the nonsymmetric Landau-Zener tunneling of Bose-Einstein condensates in deep optical lattices is presented. It is shown that periodic exchange of matter between the bands is described by a set of linearly coupled nonlinear Schrödinger equations. The key role of the modulational instability in rendering the interband transitions irreversible is highlighted.

We demonstrate efficient loading of neutral atoms into a magnetic waveguide produced by the magnetic fields of microfabricated current-carrying conductors. The lithographically patterned conductors on this “atom chip” can be used to make a variety of guiding and trapping structures for manipulating cold atoms and Bose-Einstein condensates. A three-chamber vacuum apparatus collects atoms in a magneto-optical trap, precools them via evaporative cooling, and delivers them to the final chamber containing the atom chip. We describe in detail how the precooled atomic cloud is transferred from a macroscopic magnetic Ioffe-Pritchard trap to the microscopic magnetic waveguide on the atom chip $21\mathrm{cm}$ away. Permanent magnets provide a confining two-dimensional quadrupole field to guide the atoms between the two chambers while longitudinally the cloud is allowed to freely expand during the transfer. Strategically placed coils are used to control the longitudinal size and speed of the atomic cloud as it is loaded on the atom chip.

We present the results of an experimental investigation of multimode intensity patterns from an optical parametric oscillator operating above threshold and show that it oscillates in 10–15 transverse modes strongly coupled through the nonlinear crystal, which makes this setup useful for future investigation of quantum correlations in the transverse plane. We describe the experimental setup for simultaneous measurements of signal and idler near- and far-field patterns and analyze the effects of various experimental complications such as walk-off and thermal index changes on the generated patterns. We also show that the oscillator can be stabilized by optical feedback, indicating a possible route for controlling the generated intensity patterns.

We propose a scheme to realize the optimal universal quantum cloning of the polarization state of the photons in context of a microwave cavity quantum electrodynamics. The scheme is based on the resonant interaction of three-level $\Lambda$-type atoms with two cavity modes. The operation requires atoms to fly one by one through the cavity. The interaction time between each of the atoms and the cavity is appropriately controlled by using a velocity selector. The scheme is deterministic, and is feasible by the current experimental technology.

Relative charge transfer cross section measurements for the excited state $\mathrm{Rb}\left(4d\right)$ with $7\mathrm{keV}$ ${\mathrm{Na}}^{+}$ is reported. The specific channels reported are ${\mathrm{Na}}^{+}+\mathrm{Rb}\left(4d_{5∕2}\right)\to \mathrm{Na}\left(nl\right)+{\mathrm{Rb}}^{+}$, where the dominant transfer cross sections channels were $nl=3d$ and $4s$. Using a combination of a magneto-optical trap and recoil ion momentum spectroscopy (MOTRIMS methodology), the cross sections were measured relative to the previously studied ${\mathrm{Na}}^{+}+\mathrm{Rb}(5s,5p)$ systems at the same collision energy.

We calculate the spin-polarization of electrons emitted in the neutralization of ${\mathrm{He}}^{+}$ ions interacting with metals. All stages of the emission process are included: the spin-dependent perturbation induced by the projectile, the excitation of electrons in Auger neutralization processes, the creation of a cascade of secondaries, and the escape of the electrons through the surface potential barrier. The model allows us to explain in quantitative terms the measured spin-polarization of the yield in the interaction of spin-polarized ${\mathrm{He}}^{+}$ ions with paramagnetic surfaces, and to disentangle the role played by each of the involved mechanisms. We show that electron-electron scattering processes at the surface determine the spin-polarization of the total yield. High energy emitted electrons are the ones providing direct information on the ${\mathrm{He}}^{+}$ ion neutralization process and on the electronic properties of the surface.

We study enhanced cooling of atoms within an optical cavity using feedback and a time-dependent pump source. The two approaches operate on the same principle by increasing the modulation of the optical potential induced by atomic motion in the cavity. We show that cooling time can be reduced by up to two orders of magnitude over conventional cavity cooling.

We present a Markovian quantum theory of friction. Our approach is based on the idea that collisions between a Brownian particle and single molecules of the surrounding medium constitute, as far as the particle is concerned, instantaneous simultaneous measurements of its position and momentum.

Universal quantum computation requiring only the Heisenberg exchange interaction and suppressing decoherence via an energy gap is presented. The combination of an always-on exchange interaction between the three physical qubits comprising the encoded qubit and a global magnetic field generates an energy gap between the subspace of interest and all other states. This energy gap suppresses decoherence. Always-on exchange couplings greatly simplify hardware specifications and the implementation of inter-logical-qubit gates. A controlled phase gate can be implemented using only three Heisenberg exchange operations all of which can be performed simultaneously.

We propose a scheme to engineer quantum superpositions of coherent states (“Schrödinger-cat states”) of propagating optical pulses. Multidimensional and multipartite cat states can be generated simply by reflecting coherent optical pulses successively from a single-atom cavity. The influences of various sources of noise, including atomic spontaneous emission and pulse-shape distortion, are characterized through detailed numerical simulation, which demonstrates the practicality of this scheme within the reach of current experimental technology.

We consider multiqubit systems and relate quantitatively the problems of generating cluster states with high values of concurrence of assistance, and of generating states with maximal bipartite entanglement. We prove an upper bound for the concurrence of assistance. We consider dynamics of spin-$1∕2$ systems that model qubits, with different couplings and possible presence of magnetic field, to investigate the appearance of the discussed entanglement properties. We find that states with maximal bipartite entanglement can be generated by an isotropic $XY$ Hamiltonian, and their generation can be controlled by the initial state of one of the spins. The same Hamiltonian is capable of creating states with high concurrence of assistance from a suitably chosen initial state. We show that the production of graph states using the Ising Hamiltonian is controllable via a single-qubit rotation of one spin-$1∕2$ subsystem in the initial multiqubit state. We show that the property of Ising dynamics to convert a product-state basis into a special maximally entangled basis is temporally enhanced by the application of a suitable magnetic field. Similar basis transformations are found to be feasible in the case of isotropic $XY$ couplings with a magnetic field.

The option of varying thickness of the fixed foil in the beam–two-foil technique has been incorporated in our experimental setup. It gives an opportunity to explore a new mode of this technique. In the current study, we have investigated the lifetime of the $1s2s2p{}^{4}P_{5∕2}^o$ level in Li-like titanium using this technique. The data showed a dependence of foil thickness of the fixed foil on the interactions of levels produced in the first foil. Average lifetime obtained for the Li-like titanium $1s2s2p{}^{4}P_{5∕2}^o$ level $(200\pm 12\mathrm{ps})$ is compared very well with the earlier theoretical and experimental values.

We develop a theoretical treatment of the dissociative recombination of triatomic molecular ions of the $C_{2v}$ molecular symmetry group. Using the method, we study the dissociative recombination of the ${\mathrm{H}}_2{\mathrm{D}}^{+}$ and ${\mathrm{D}}_2{\mathrm{H}}^{+}$ ions. The theoretical rates obtained for the ${\mathrm{H}}_2{\mathrm{D}}^{+}$ and ${\mathrm{D}}_2{\mathrm{H}}^{+}$ dissociative recombination are in general agreement with storage-ring experiments although there are some potentially informative discrepancies.

By measuring the relaxation rates of the nuclear spin polarization of ${}^{129}\mathrm{Xe}$ in the presence of alkali-metal vapor at different densities, we have extracted the spin-exchange rates between ${}^{129}\mathrm{Xe}$ and the three alkali metals K, Rb, and Cs. By studying the alkali-metal–${}^{129}\mathrm{Xe}$ spin-exchange rates as functions of the cell number density from 0.2 to 0.7 amagat, the binary collision and van der Waals molecular terms are separated, and constants governing both mechanisms are determined. The results from our work can be used to optimize the parameter space for polarizing ${}^{129}\mathrm{Xe}$, a promising agent for magnetic resonance imaging and other applications.

We study the possibility of associating metastable Efimov trimers from three free Bose atoms in a tight trap realized, for instance, via an optical lattice site or a microchip. The suggested scheme for the production of these molecules is based on magnetically tunable Feshbach resonances and takes advantage of the Efimov effect in three-body energy spectra. Our predictions of the energy levels and wave functions of three pairwise interacting ${}^{85}\mathrm{Rb}$ atoms rely upon exact solutions of the Faddeev equations and include the tightly confining potential of an isotropic harmonic atom trap. The magnetic field dependence of these energy levels indicates that it is the lowest-energetic Efimov trimer state that can be associated in an adiabatic sweep of the field strength. We show that the binding energies and spatial extents of the trimer molecules produced are comparable, in their magnitudes, to those of the associated diatomic Feshbach molecule. The three-body molecular state follows Efimov’s scenario when the pairwise attraction of the atoms is strengthened by tuning the magnetic field strength.

The chemi-ionization processes in slow-atom–Rydberg-atom collisions are considered in this paper. A version of the semiclassical method of rate coefficient calculation that is free of the presumptions which significantly limited its applicability previously is presented. The method is applied to the cases of ${\mathrm{Li}}^{*}\left(n\right)+\mathrm{Li}$ and ${\mathrm{Na}}^{*}\left(n\right)+\mathrm{Na}$ collisions for the principal quantum numbers $5⩽n⩽25$ and temperatures $600⩽T⩽1200\mathrm{K}$. The results of calculation of the rate coefficients of the corresponding chemi-ionization processes are compared to the existing experimental data from the literature.

A study of the autoionization process induced by partially stripped ion impact is performed. Electron spectra in momentum space are predicted within a classical model for partially stripped ions. The results are compared with those obtained for pure Coulomb-like projectiles. A quantum-mechanical extension of the Barrachina-Macek model is proposed for partially stripped projectiles. Structure on the electron angular distribution arising in quantum and classical treatments is identified and compared. The presence of rainbow scattering interference is observed in the binary ring profile of the outgoing autoionized electrons for positive-ion impact.