We use double-resonance photoassociative spectroscopy of ultracold ${}^{39}\mathrm{K}$ atoms to precisely determine the triplet $a{}^3{\Sigma }_u^{+}$ scattering length for the various isotopes of potassium. Photoassociation of free ${}^{39}\mathrm{K}$ atoms to the pure long-range $0_g^{-}{(v}^{\prime }=0,J^{\prime }=2)$ level is followed by stimulated emission to high-lying levels of the $a{}^3{\Sigma }_u^{+}$ potential. The binding energies of levels within 5 GHz below the lowest ground-state ${4s}_{1/2}{(f}_a{=1)+4s}_{1/2}{(f}_b=1)$ hyperfine asymptote are measured by both trap loss and ionization detection. The locations of these near-threshold hyperfine-coupled molecular levels allow us to constrain the triplet potential and thereby determine the triplet scattering length. The result for ${}^{39}\mathrm{K},$ $a_t=-33\pm {5a}_0$ ${(1a}_0=0.052\mathrm{}9177\hspace{0.5em}\mathrm{nm}),$ is a factor of $\sim 5$ improvement over previous determinations and establishes that a large ${}^{39}\mathrm{K}$ Bose-Einstein condensate will not be stable.

We construct an analytical wave function in the phase-amplitude formalism to describe collisions between two neutral atoms. This wave function is valid from intermediate to asymptotic internuclear distance over a large energy range near zero energy, and is especially suitable for cold and ultracold collisions. We have used this analytic wave function with the reflection approximation formula for calculating Franck-Condon factors for photoassociative spectroscopy. Numerical tests show very satisfactory agreement between the resulting analytic formula and the fully quantum numerical results in most cases investigated. Finally, we show in a model case that our analytical wave function enables us to relate the scattering length directly to a preasymptotic node in the ground-state wave function, which in principle can be measured by photoassociative spectroscopy.

The single-electron capture (SEC) process which occurs in ${\mathrm{Ar}}^{8+}$-$\mathrm{Cs}\mathrm{}\left(6s\right)\mathrm{}$ collisions is experimentally studied, in the 0.4–5-keV/amu energy range, by optical spectroscopy in the near UV and visible wavelength range (200–600 nm). The classical-trajectory Monte Carlo (CTMC) method is also used to determine the state-selective electron-capture cross sections. For high collision energies, strong lines corresponding to $\Delta n=1\mathrm{}$–4 transitions from $n=7\mathrm{}$ to 13 states with large angular momentum values of Ar VIII and $\Delta n=0\mathrm{}$ transitions from $n=5\mathrm{}$ states are observed. For low collision energies, together with the lines observed for high collision energies, lines corresponding to transitions from states with low-$l$ values $(10s,$ $11s,$ and $13s)$ are detected. Production cross sections for the most populated levels $(n=9,$ 10, and 11) are determined and compared with the previous experimental data of Martin et al. [Phys. Rev. A 46, 1316 (1992)] and Denis et al. [Phys. Rev. A 50, 2263 (1994)], and with the CTMC calculations. From molecular structure calculations which are performed for the $\{{\mathrm{Ar}}^{7+}+\mathrm{Cs}{\}}^{+}$ molecular system, our results are analyzed in terms of dynamical couplings between the relevant molecular channels involved in the electron-capture process. Polarization degrees for SEC lines corresponding to transitions between high-$l$ values states are also measured. The comparison with those calculated from the CTMC results provides information about the Zeeman sublevel distributions.

Ignition of lithium glow discharge below self-breakdown voltage is studied for three cases of laser excitation of lithium vapor: the quasiresonant line at 460.3 nm $\left(2\mathrm{}\overrightarrow{p}4d\right),$ the two-photon resonant line at 639.1 nm $(2\mathrm{}\overrightarrow{s}3d$ transition), or the first resonance at 670.8 nm $(2\mathrm{}\overrightarrow{s}2p$ transition). The conditions for laser ignition of the discharge are described. The differences between the self-breakdown voltage and the breakdown voltage for laser initiation of the discharge are given for different lithium number densities.

The fragmentation patterns of the halomethanes ${\mathrm{CCl}}_2{\mathrm{F}}_2,$ ${\mathrm{CClF}}_3,$ ${\mathrm{CF}}_4,$ and ${\mathrm{CHF}}_3$ have been studied by positron impact, in the energy range from threshold to around 50 eV. These data were obtained using a quadratic potential time of flight mass spectrometer, coupled with a Penning trap and a LINAC-based positron source. The present data for positrons are compared with results for electron and photoionization from other works.

Beams of 10-MeV/amu Ne, Ar, Cr, Kr, Xe, and Bi ions have been employed to examine the dependence on projectile atomic number ${(Z}_1)$ of Al K-shell vacancy production in nearly symmetric ${(Z}_1{/Z}_2=0.8)$ to highly asymmetric ${(Z}_1{/Z}_2=6.4)$ collisions. Aluminum K x-ray yields were measured with a Si(Li) detector as a function of target thickness to establish cross sections for charge equilibrated projectiles. Average target atom L-shell vacancy distributions excited in K-shell vacancy-producing collisions and x-ray yield corrections for contributions from photoionization and secondary electron impact were deduced from high-resolution spectral measurements performed with a curved-crystal spectrometer. Knowledge of the average L-shell vacancy distributions provided the means for estimating the appropriate fluorescence yields needed to convert the x-ray yields to K-shell vacancy production cross sections. Theoretical cross sections greatly overestimate the experimental results for $Z_1>10.\mathrm{}$ The $Z_1$ dependences of the K-shell vacancy production cross sections for both Al and Cu (from a previous study) are well characterized by a simple empirical scaling law.

The phenomenon of coherent microwave stimulated emission in a cavity is analyzed for the case of alkali atoms such as Cs and Rb under coherent population trapping (CPT) in a Λ scheme. The calculations are made in transient and in continuous operation within the framework of a three level model. The coupling of the atoms to the microwave field generated inside the cavity by the atomic ensemble, is fully taken into account; it introduces radiation damping and an imbalance in the populations of the ground-state hyperfine levels, decreasing the intrinsic symmetry of the Λ scheme. The effect leads also to a broadening and to a frequency shift of the microwave emission profile. A comparison is made with the optically pumped alkali atom maser, allowing a deeper understanding of the CPT stimulated emission phenomenon.

We analyze strong field atomic dynamics semiclassically, based on a full time-dependent description with the Hermann-Kluk propagator. From the properties of the exact classical trajectories, in particular the accumulation of action in time, the prominent features of above-threshold ionization and higher-harmonic generation are proven to be interference phenomena. They are reproduced quantitatively in the semiclassical approximation. Moreover, the behavior of the action of the classical trajectories supports the so called strong field approximation which has been devised and postulated for strong field dynamics.

We report in detail our complete characterization of atomic photoionization via a single measurement, namely, that of the two-photon photoelectron angular distribution using elliptically polarized light. Through these measurements we are able to determine the atomic parameters necessary to unambiguously describe two-photon ionization of atomic rubidium. These parameters include relative cross sections for photoionization into various outgoing channels as well as the phase difference between the continuum S and D partial waves. We present a derivation of the angular distribution with arbitrarily polarized light in terms of these cross sections and phases, demonstrate the advantages of using elliptically polarized light, discuss details of the experiment, and report the results of our measurements in this paper. While measured phase differences are in excellent agreement with expected values over the entire range of photoelectron kinetic energy of our measurements from 0 to 0.5 eV, ratios of cross sections for photoionization into the two D channels are anomalous, suggesting unexpected fine structure effects in these continua.

An expression for the van der Waals interaction between an active atom and a perturber atom is derived using an irreducible tensor representation. This interaction leads to magnetic state decoherence in an ensemble of active atoms. The magnetic state decoherence can be suppressed by the application of ultrafast optical pulses. It is shown that the depolarization cross section can be suppressed by as much as 40% with only four optical pulses during a single collision and that, for a large number of pulses, the cross section is proportional to $n_0^{-2/11}$ where $n_0$ is the number of pulses at the Weisskopf radius. This paper generalizes our previous results in which the collisional interaction was modeled as a square pulse.

The three-dimensional time-dependent Schrödinger equation is solved exactly for the ${\mathrm{H}}_2^{+}$ molecular ion as a function of internuclear distance R in a short intense laser field pulse and a static magnetic field, parallel to the internuclear axis, using a numerical integration method. Previous calculations of laser-induced ionization in this ion for zero magnetic field [Phys. Rev. A 48, 3837 (1993); 52, 2511 (1995)] demonstrated the phenomenon of charge-resonance-enhanced ionization (CREI) at critical distances $R_c,$ due to Stark displacements of the lowest unoccupied molecular orbital (LUMO) above internal proton Coulomb and static laser field barriers. The presence of the magnetic field allows for controlling the energy displacements of the LUMO and consequently control of CREI, thus confirming CREI as a quasistatic electron tunneling process in the nonsymmetric double-well potential created by protons and a laser field.

A formalism for studying spontaneous decay of an excited two-level atom in the presence of dispersing and absorbing dielectric bodies is developed. An integral equation, which is suitable for numerical solution, is derived for the atomic upper-state-probability amplitude. The emission pattern and the power spectrum of the emitted light are expressed in terms of the Green tensor of the dielectric-matter formation, including absorption and dispersion. The theory is applied to the spontaneous decay of an excited atom at the center of a three-layered spherical cavity, with the cavity wall being modeled by a band-gap dielectric of Lorentz type. Both weak and strong coupling are studied, the latter with a special emphasis on cases where the atomic transition is (i) in the normal-dispersion zone near the medium resonance, and (ii) in the anomalous-dispersion zone associated with the band gap. In a single-resonance approximation, conditions of the appearance of Rabi oscillations and closed solutions to the evolution of the atomic state population are derived, which are in good agreement with the exact numerical results.

The time evolution equations for average values of population and relative phase of a strongly coupled two-component Bose-Einstein condensate (BEC) are derived analytically. The two components are two hyperfine states, which are coupled by an external laser that drives fast Rabi oscillations between these states. Specifically, this derivation incorporates the two-mode model proposed in J. Williams et al., e-print cond-mat 9904399 for the strongly coupled hyperfine states $|1,-1〉$ and $|2,1〉$ of ${}^{87}\mathrm{Rb}.$ The fast Rabi cycles are averaged out and the rate equations so derived represent the slow dynamics of the system. These include the collapse and revival of Rabi oscillations and their dependence on detuning and trap displacement as reported in experiments of J. Williams. A procedure for stabilizing vortices is also suggested.

We have performed classical trajectory Monte Carlo studies of electron capture and ionization in multiply charged $(Q<~8)$ ion–Rydberg-atom collisions at intermediate impact velocities. Impact parallel to the minor and to the major axis, respectively, of the initial Kepler electron ellipse has been investigated. The important role of the initial electron momentum distribution found for singly charged ion impact is strongly diminished for higher projectile charge, while the initial spatial distribution remains important for all values of Q studied.

We present measurements of the steady-state temperature in a three-dimensional cesium optical lattice, operating in the near-resonance regime of the $D2\mathrm{}$ line. For various detunings between the ${(F}_g=\overrightarrow{4}{F}_e=5)$ and the ${(F}_g=\overrightarrow{4}{F}_e=4)$ transitions, we systematically determine at which intensities/optical potential modulation depths the Sisyphus cooling process breaks down and what the lowest achievable temperatures are. We find that the minimum temperature decreases as we increase the detuning with respect to the ${(F}_g=\overrightarrow{4}{F}_e=5)$ transition.

We report on the microscopic imaging of individual sites of an optical lattice with a period of 5.3 μm created by a retroreflected, focused ${\mathrm{CO}}_2$-laser beam. In this one-dimensional lattice, the Lamb-Dicke limit is fulfilled in all three spatial dimensions. Single lattice sites have been individually addressed with a focused near-resonant laser beam. Because of the negligible decoherence rate from spontaneous photon scattering such a lattice holds intriguing prospects for the realization of fault-tolerant quantum logic gates.

We have performed relativistic many-body calculations of the hyperfine interaction in the $6s$ and $7s$ states of Cs, including the off-diagonal matrix element. The calculations were used to determine the accuracy of the semiempirical formula for the electromagnetic transition amplitude $〈6s|M1\mathrm{}|7s〉$ induced by the hyperfine interaction. We have found that even though the contribution of the many-body effects into the matrix elements is very large, the square-root formula $〈6s|H_{\mathrm{hfs}}|7s〉=\sqrt{〈6s|H_{\mathrm{hfs}}|6s〉〈7s|H_{\mathrm{hfs}}|7s〉}$ remains valid to the accuracy of a fraction of ${10}^{-3}.$ The result for the M1- amplitude is used in the interpretation of the parity-violation measurement in the $6s-7s$ transition in Cs, which claims a possible deviation from the standard model.

Previous work on Bell’s inequality realized in the laboratory has used entangled photons. Here we describe how entangled atoms can violate Bell’s inequality, and how these violations can be measured with a very high detection efficiency. We first discuss a simple scheme based on two-level atoms inside a cavity to prepare the entangled state. We then discuss a scheme using three-level atoms, which requires a parameter regime much easier to access experimentally using current technology. As opposed to other schemes, our proposal relies on the presence of finite decay rates and its implementation should therefore be much less demanding.

We propose an implementation for quantum logic and computing using trapped atomic spins of two different species, interacting via direct magnetic spin-spin interaction. In this scheme, the spins (electronic or nuclear) of distantly spaced trapped neutral atoms serve as the qubit arrays for quantum information processing and storage, and the controlled interaction between two spins, as required for universal quantum computing, is implemented in a three-step process that involves state swapping with a movable auxiliary spin.

It is not possible to disentangle a qubit in an unknown state $|\psi 〉$ from a set of $N-1$ ancilla qubits prepared in a specific reference state $|0〉.$ That is, it is not possible to perfectly perform the transformation $(|\psi ,0,\dots ,0\mathrm{}〉+|0,\psi ,\dots ,0\mathrm{}〉+\cdot \cdot \cdot +|0,0,\dots ,\psi 〉)\to |0,\dots ,0\mathrm{}〉\otimes |\psi 〉.$ The question is then how well we can do? We consider a number of different methods of extracting an unknown state from an entangled state formed from that qubit and a set of ancilla qubits in a known state. Measuring the whole system is, as expected, the least effective method. We present various quantum “devices” which disentangle the unknown qubit from the set of ancilla qubits. In particular, we present the optimal universal disentangler which disentangles the unknown qubit with a fidelity that does not depend on the state of the qubit, and a probabilistic disentangler which performs the perfect disentangling transformation, but with a probability less than 1.