We have investigated K-shell vacancy production due to ionization and electron transfer processes, in collisions of highly charged oxygen ions with various solid targets such as Cl, K, Ti, Fe, and Cu at energies between 1.5 and 6.0 MeV/u. The K-shell ionization cross sections were derived from the measured K x-ray cross sections. An ab initio theoretical model based on the local plasma approximation (LPA), which is an extension of the dielectric formalism to consider core electrons, provides an explanation of the measured data only qualitatively. In case of asymmetric collisions ${(Z}_p{/Z}_t<0.35,$ $Z_p,$ $Z_t$ being the atomic numbers of the projectile and target, respectively) and at higher energies, the LPA model explains the data to some extent but deviates for more symmetric collision systems. On the other hand, a perturbed-stationary-state (PSS) calculation (ECPSSR), including the corrective terms due to energy (E) loss, Coulomb (C) deflection, and relativistic (R) wave functions designed for ion-atom collisions agree quite well with the data for different combinations of target and projectile elements. In addition, we have also measured the $K\left(\mathrm{target}\right)-K\left(\mathrm{projectile}\right)\hspace{0.5em}\mathrm{electron}$ transfer cross sections and compared them with a model based on perturbed-stationary-state approximation.

We propose a converging algorithm allowing to reconstruct phase shifts in a broad range of momenta using low-energy scattering data and information about bound states (if supported by the potential).

The dynamics of an ensemble of highly charged Ar and Ba ions in an electron-beam ion trap (EBIT) was studied by recording time-resolved x-ray spectra emitted from trapped ions. Sawtoothlike signatures manifest in the spectra for a variety of EBIT operating conditions indicating a sudden collapse of the ion inventory in the trap. The collapse occurs on a time scale of approximately 100 ms and the evolution of the sawteeth is very sensitive to parameters such as electron-beam current and axial trap depth. Analysis of the measurements is based on a time-dependent calculation of the trapping process showing that sawtooth activity is caused by the feedback between the low-$Z$ argon and high-$Z$ barium ions. This unexpected behavior demonstrates the importance of nonlinear effects in electron-beam traps containing more than a single ion species.

Gadolinium occurs, in natural abundance, as several isotopes. The possible combinations of different gadolinium isotopes dictates that even for a fixed number of atoms in the cluster, clusters of gadolinium atoms will exhibit a range of masses. This and the expected consequence of the translation energy distributions are explored as possible corrections to Stern-Gerlach cluster beam-deflection experiments. Upon closer inspection of the experimental data, we find that the translation energy plus the vibrational temperature distribution may be inhomogeneous. This could be the origin of a long tail to high deflections in the experimental deflection profiles, at low cluster temperatures, in the magnetic cluster Stern-Gerlach experiments.

The dynamics induced while controlling quantum systems by optimally shaped laser pulses have often been difficult to understand in detail. A method is presented for quantifying the importance of specific sequences of quantum transitions involved in the control process. The method is based on a “beable” formulation of quantum mechanics due to John Bell that rigorously maps the quantum evolution onto an ensemble of stochastic trajectories over a classical state space. Detailed mechanism identification is illustrated with a model seven-level system. A general procedure is presented to extract mechanism information directly from closed-loop control experiments. Application to simulated experimental data for the model system proves robust with up to 25% noise.

Angle- and energy-dependent cross sections for electron emission were measured for 68-MeV/u ${\mathrm{Kr}}^{33+}$ ions impacting on ${\mathrm{H}}_2.$ These results show, in accordance with our earlier observation, that interference effects are produced by the coherent emission of electrons from the two H atoms, in analogy with Young’s two-slit experiment. Furthermore, the present results demonstrate that the observed oscillatory pattern varies with the electron observation angle, contrary to our earlier expectations but in agreement with recent theoretical predictions.

We show that atomic Fermi gases in quasi-two-dimensional (2D) geometries are promising for achieving superfluidity. In the regime of BCS pairing for weak attraction, we calculate the critical temperature $T_c$ and analyze possibilities of increasing the ratio of $T_c$ to the Fermi energy. In the opposite limit, where a strong coupling leads to the formation of weakly bound quasi-2D dimers, we find that their Bose-Einstein condensate will be stable on a long time scale.

We demonstrate that it is possible to choose an optimal signal mode for state reconstruction when performing quantum-state tomography with array detectors. The mode optimization is done during the data analysis (i.e., after all the data have been collected.) We develop theoretically a procedure for finding the mode that satisfies a criterion which is quadratic in field operators; as examples we explicitly show how to maximize the average photon number, or the amount of quadrature squeezing. We experimentally demonstrate the technique by finding the mode which maximizes the average photon number for coherent-state signal beams occupying both linear and sinusoidal modes.

There exists a class of relativistic electric-dipole matrix-element zeros which occur in $\mathrm{}(n,l,j)\mathrm{}\to (\epsilon ,l+1,j)$ transitions at the photon energy ${\omega }^0{=mc}^2/(l+1\mathrm{}),$ independent of the potential $V$ as well as n and Z. These zeros do have observable physical consequences, despite the fact that they occur at high energies where multipole matrix elements are important.

Cross sections for the photoionization (PI) of ${\mathrm{Sc}}^{2+}$ ions with $\left[\mathrm{Ar}\right]3d$ ground-state configuration have been measured by employing the merged ion-photon beams method. The ${\mathrm{Sc}}^{2+}$ ions were produced from metallic vapor in an electron cyclotron resonance ion source, and the photon beam was generated by an undulator in the electron-synchrotron storage ring of the advanced light source of the Lawrence Berkeley National Laboratory. The experimental photon energy range 23–68 eV encompasses the direct $3d$ and $3p$ photoionization thresholds. The experimental photoion spectrum is dominated by autoionizing resonances due to $3p$ excitations predominantly decaying via Coster-Kronig and super-Coster-Kronig transitions. Individual resonances located around $E\approx 40.2\mathrm{eV}$ have been measured with an instrumental energy spread $\Delta E$ as low as 1.2 meV, corresponding to a resolving power of $E/\left(\Delta E\right)$ around 33 500. The fractions of metastable ions in the ${\mathrm{Sc}}^{2+}$ ion beam are obtained by comparing the photoionization cross section with the recently measured [Schippers et al., Phys. Rev. A 65, 042723 (2002)] cross section for the time-reversed process of photorecombination of ${\mathrm{Sc}}^{3+}$ ions. Absolute strengths of several ${3p}^5{3d}^2$ and ${3p}^{5}3d4s$ PI resonances have been determined. They are the same as the corresponding resonance strengths for isoelectronic ${\mathrm{Ca}}^{+}$ ions.

In some respects, a cluster consisting of many atoms may be regarded as a single large atom. Knowing the dielectric properties of such a cluster permits one to evaluate the form of the van der Waals (dispersion) interactions between two clusters or between one cluster and a surface. In this paper, we derive these interactions in two extreme opposite regimes of separation: fully retarded and nonretarded. In the fully retarded regime (very large separation), the magnitude of the interaction is determined by just the static polarizability of the cluster(s). In the nonretarded regime (small separation), we employ a single resonant frequency model of the cluster polarizability to derive expressions for the interactions’ coefficients. Numerical examples are presented to demonstrate that many-body screening of these interactions can be significant. The results represent the corrections to the commonly used approximation of pairwise additivity of interatomic interactions.

We theoretically investigate the ground-state properties and quantum dynamics of a pair of adjacent ring-shaped Bose-Einstein condensates that are coupled via tunneling. This device, which is the analog of a symmetric superconducting quantum interference device, is the simplest version of what we term an atomic-phase interference device (APHID). The two-ring APHID is shown to be sensitive to rotation.

Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of elementary excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons—sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable.

We experimentally demonstrate quantum teleportation for continuous variables using squeezed-state entanglement. The teleportation fidelity for a real experimental system is calculated explicitly, including relevant imperfection factors such as propagation losses, detection inefficiencies, and phase fluctuations. The inferred fidelity for input coherent states is $F=0.61\mathrm{}\pm 0.02,$ which when corrected for the efficiency of detection by the output observer, gives a fidelity of $\mathrm{0.62.}$ By contrast, the projected result based on the independently measured entanglement and efficiencies is $\mathrm{0.69.}$ The teleportation protocol is explained in detail, including a discussion on discrepancy between experiment and theory, as well as on the limitations of the current apparatus.

In a recent proposal for a quantum cryptographic scheme analogous to one out of two oblivious transfers [Phys. Rev. A 66, 052316 (2002)], a sender, Bob, can encode two bits of information (X,Y) in a quantum carrier but a receiver, Alice, can decode only either X or Y dependent on her choice. Although Bob can discover her choice whenever he desires, she can detect this with a 50% probability. This paper clarifies the amount of information that Bob can expect to obtain from Alice without being detected by her by means of an Einstein-Podolsky-Rosen (EPR) type of attack. We can show that Bob inevitably fails to discover her choice with a 50% probability even though he can always completely escape her detection.

We derive a simple asymptotic expression for the screened Casimir free energy that is valid in both the high-temperature limit and in the large-separation limit. Any finite (i.e., nonzero) plasma density fundamentally alters the long-range interaction. The similarity of the derived expression with the Yukawa potential of nuclear interactions encourages us to investigate the Casimir free energy between two nuclear particles in a sea of electrons and positrons. We use simple estimates to explore the possible role of screened Casimir interactions for nuclear interactions. The magnitude of the force and of the coupling constant indicates an intriguing possible interpretation in which the nuclear force is a screened Casimir force and the mesons can be viewed as plasmons in the electron-positron sea.

Weak nuclear coupling between the nucleons of a molecule and its electrons causes the energy and electronic wave function to be different for two enantiomers of a chiral molecule, i.e., for two molecules which are the specular image of each other. Although this effect has been known for some time, its magnitude is so small that all attempts made so far at measuring it experimentally have failed. We report in this paper computational estimates of vibrational frequency shifts due to parity-violation energy near or above current experimental resolution. Our findings indicate that an experimental evidence of parity-violation effects in molecular systems is within reach.

The two-qubit interaction Hamiltonian of a given physical implementation determines whether or not a two-qubit gate such as the controlled-NOT (CNOT) gate can be realized easily. It can be shown that, e.g., with the $\mathrm{XY}$ interaction more than one two-qubit operation is required in order to realize the CNOT operation. Here we propose a two-qubit gate for the $\mathrm{XY}$ interaction which combines the CNOT and SWAP operations. By using this gate quantum circuits can be implemented efficiently, even if only nearest-neighbor coupling between the qubits is available.

We report the experimental demonstration of quantum teleportation of the quadrature amplitudes of a light field. Our experiment was stably locked for long periods, and was analyzed in terms of fidelity $\mathcal{F}$ and with signal transfer $T_q{=T}^{+}{+T}^{-}$ and noise correlation $V_q{=V}_{\mathrm{in}\mathrm{|}\mathrm{}\mathrm{out}}^{+}{V}_{\mathrm{in}\mathrm{|}\mathrm{}\mathrm{out}}^{-}.$ We observed an optimum fidelity of $0.64\pm 0.02,$ $T_q=1.06\mathrm{}\pm 0.02,$ and $V_q=0.96\mathrm{}\pm \mathrm{0.10.}$ We discuss the significance of both $T_q>1\mathrm{}$ and $V_q<1\mathrm{}$ and their relation to the teleportation no-cloning limit.

The frequency of the $5s{}^2{S}_{1/2}$–$4d{}^2{D}_{5/2}$ electric quadrupole transition at 674 nm in a single, trapped, laser-cooled ${}^{88}{\mathrm{Sr}}^{+}$ ion has been measured with respect to the Système International (SI) second using a femtosecond laser optical frequency comb. The measured frequency of 444 779 044 095.52 kHz, with an estimated standard uncertainty of 0.10 kHz, is more accurate than, and in agreement with, the value previously measured using a conventional frequency chain.