We study the interaction of two localized impurities in a repulsive one-dimensional Fermi liquid via bosonization. In a previous paper [Phys. Rev. A 72, 023616 (2005)], it was shown that at distances much larger than the interparticle spacing the impurities interact through a Casimir-type force mediated by the zero-sound phonons of the underlying quantum liquid. Here we extend these results and show that the strength and sign of this Casimir interaction depend sensitively on the impurity separation. These oscillations in the Casimir interaction have the same period as Friedel oscillations. Their maxima correspond to tunneling resonances tuned by the impurity separation.

An experiment which could decide against the Copenhagen interpretation of quantum mechanics has been proposed by K. Popper and, subsequently, it has been criticized by M. J. Collett and R. Loudon. Here we show that both the above-mentioned arguments are not correct because they are based on a misuse of basic quantum rules.

A complete and deterministic Bell state measurement was realized by a simple linear optics experimental scheme which adopts two-photon polarization-momentum hyperentanglement. The scheme, which is based on the discrimination among the single photon Bell states of the hyperentangled state, requires the adoption of standard single photon detectors. The four polarization Bell states have been measured with average fidelity $F=0.889\pm 0.010$ by using the linear momentum degree of freedom as the ancilla. The feasibility of the scheme has been characterized as a function of the purity of momentum entanglement.

We present a method for performing quantum-state reconstruction on qubits and qubit registers in the presence of decoherence and inhomogeneous broadening. The method assumes only rudimentary single-qubit rotations as well as knowledge of decoherence and loss mechanisms. We show that full state reconstruction is possible even in the case where single-qubit rotations may only be performed imperfectly. Furthermore, we show that for ensemble quantum-computing proposals, quantum-state reconstruction is possible even if the ensemble experiences inhomogeneous broadening and if only imperfect qubit manipulations are available during state preparation and reconstruction.

The low-lying $n(=3,4,5)d$ ${}^{2}D_{5∕2}$ states of alkaline-earth-metal ions are of vital importance in a number of different physical applications. The hyperfine structure constants of these states are characterized by unusually strong electron correlation effects. Relativistic coupled-cluster theory has been employed to carry out ab initio calculations of these constants. The role of the all-order core-polarization effects was found to be decisive in obtaining good agreement of our calculated magnetic dipole hyperfine structure constants with accurate measurements. The present work is an apt demonstration of the power of the coupled-cluster method to cope with strongly interacting configurations.

The decay of protonated DNA dinucleotides, $\mathrm{dA}_2{}^{+}$, $\mathrm{dG}_2{}^{+}$, $\mathrm{dT}_2{}^{+}$, $\mathrm{dC}_2{}^{+}$ and deprotonated ones, $\mathrm{dA}_2{}^{-}$ and $\mathrm{dT}_2{}^{-}$, after $260\mathrm{nm}$ photon absorption was measured in an electrostatic ion storage ring (A denotes adenine, G guanine, T thymine, and C cytosine). Fragmentation on the microsecond time scale was observed and assigned to statistical dissociation. Good fits to the decay spectra were obtained with a model based on microcanonical rate constants of the Arrhenius type with activation energies and preexponential factors for the dissociation that agree well with literature values. In accordance with results from other groups, $\mathrm{dT}_2{}^{+}$ was found to have the longest lifetime among the cations. The importance of decay processes faster than the microsecond time scale is elucidated by a comparison between the total ion beam depletion and that due to the observed statistical decay. We find that such processes play a major role for all of the dinucleotides, being more than 25 times more probable than the microsecond statistical dissociation for $\mathrm{dA}_2{}^{+}$, $\mathrm{dG}_2{}^{+}$, and $\mathrm{dC}_2{}^{+}$, about 10 times for $\mathrm{dT}_2{}^{+}$, and between 2 and 6 times for $\mathrm{dA}_2{}^{-}$ and $\mathrm{dT}_2{}^{-}$. For the cations, we ascribe these processes to nonstatistical dissociation prior to randomization of the excitation energy among all degrees of freedom whereas direct photoelectron detachment may play a role for the anions. Thus, our data indicate that the propensity for nonstatistical dissociation increases upon nucleobase protonation. Consistent with this trend, the propensity is less for $\mathrm{dT}_2{}^{+}$ than for the other dinucleotide cations because the phosphoric acid group competes with thymine for the proton.

The transmission of incident $10–20\mathrm{keV}∕q$ ${\mathrm{Ar}}^{+}$, ${\mathrm{Ar}}^{3+}$, ${\mathrm{Ne}}^{3+}$, and ${\mathrm{Ne}}^{7+}$ ions in an ${\mathrm{Al}}_2{\mathrm{O}}_3$ nanocapillary array was studied. The array consists of a dense distribution of pores typically $100\mathrm{nm}$ in diameter and $60\mathrm{\mu }\mathrm{m}$ in length. Emergent charge-state-selected angular distributions were studied at low energy using a two-dimensional (2D) position sensitive detector. The principal transmitted $q$ state is the incident $q$ state in all cases. The transmitted fraction of incident beam, $\approx 2\times {10}^{-8}$, is many orders of magnitude smaller than the array’s surface porosity $(\approx 40\%)$. No evidence of significant energy loss is observed for the transmitted ions. Yields in lower $q$ states and neutrals formed by electron capture are typically below 3% of the entrance $q$-state yield. Observed angular distributions consist of well resolved, 2D structures sitting on a continuum distribution. The angular distribution and sharp angular structures can be steered in the direction of the pores within about $\pm 0.5°$ without a significant loss of transmitted intensity by rotating the sample with respect to the incident beam. All data suggest that the structure in the scattered ion angular distributions arises when ions bounce at ultralow grazing angles in very large impact parameter Coulomb collisions with electrically charged nanopore walls. Analysis of the observed structure has allowed the identification of single, double, and triple collisions inside the nanopores.

A description of photoassociation by cw laser is formulated in the framework of grid methods. The Hamiltonian describing one or several bound states coupled to a multiple of continuum manifolds via a radiative field is written in the energy representation and diagonalized. The generality of the treatment allows us to compute accurately and efficiently physical properties such as nonlinear high-intensity energy shifts, line shapes, and photoassociation rates both for isolated and nonisolated resonances. Application is given to sodium photoassociation in the experimental conditions of McKenzie et al. [Phys. Rev. Lett. 88, 090403 (2002)]. Inverted regions for the dependency of the rate vs the intensity and nonsymmetric line shapes are predicted to occur above the saturation limit. Comparison with the model of Bohn and Julienne [Phys. Rev. A 60, 414 (1999)] is discussed.

We investigate the influence of the Coulombic nature of the binding potential on high-order harmonic generation in ${\mathrm{H}}_2^{+}$ molecules. We show that two-center interference effects are predicted accurately using approximated two-center Coulomb wave functions for the electron continuum state in the recombination amplitude that determines the probability for harmonic emission upon recollision.

We perform the first numerical three-dimensional studies of quantum field effects in the Bosenova experiment on collapsing condensates by E. Donley et al. [Nature (London) 415, 39 (2002)] using the exact experimental geometry. In a stochastic truncated Wigner simulation of the collapse, the collapse times are larger than the experimentally measured values. We find that a finite temperature initial state leads to an increased creation rate of uncondensed atoms, but not to a reduction of the collapse time. A comparison of the time-dependent Hartree-Fock-Bogoliubov and Wigner methods for the more tractable spherical trap shows excellent agreement between the uncondensed populations. We conclude that the discrepancy between the experimental and theoretical values of the collapse time cannot be explained by Gaussian quantum fluctuations or finite temperature effects.

The shear viscosity of a two-component Fermi gas in the normal phase is calculated as a function of temperature in the unitarity limit, taking into account strong-coupling effects that give rise to a pseudogap in the spectral density for single-particle excitations. The results indicate that recent measurements of the damping of collective modes in trapped atomic clouds can be understood in terms of hydrodynamics, with a decay rate given by the viscosity integrated over an effective volume of the cloud.

We have observed Ba $6s(n+3)d{}^{1}D_2-6sng{}^{1}G_4$ two-photon microwave transitions for $31⩽n⩽44$. We observe $400\text{−}\mathrm{kHz}$-wide lines in spite of the Earth’s magnetic field of $0.5\mathrm{G}$. The lines are so narrow since the transitions are between states with the same $g_j$ factor, so that all $\Delta m_j=0$ transitions occur at the same frequency. These measurements provide an order-of-magnitude improvement in the $6snd$ quantum defects and confirm the energies predicted by a multichannel quantum defect theory analysis for this perturbed region of the spectrum.

The mode-mode entanglement between trapped ions and cavity fields is investigated in the dispersive regime. We show how a simple initial preparation of Gaussian coherent states and a postselection may be used to generate motional nonlocal mesoscopic states involving ions in different traps. We also present a study of the entanglement induced by dynamical Stark shifts considering a cluster of $N$ trapped ions. In this case, all entanglement is due to the dependence of the Stark shifts on the ions’ state of motion manifested as a cross-Kerr interaction between each ion and the field.

We consider quantum error-correction codes for multimode bosonic systems, such as optical fields, that are affected by amplitude damping. We demonstrate that the most accessible method of transforming optical systems with the help of passive linear networks has limited usefulness in preparing and manipulating such codes. These limitations stem directly from the recoverability condition for one-photon loss. We introduce a three-photon code protecting against the first order of amplitude damping, i.e., a single photon loss, and discuss its preparation using linear optics with single-photon sources and conditional detection. Quantum state and process tomography in the code subspace can be implemented using passive linear optics and photon counting. An experimental proof-of-principle demonstration of elements of the proposed quantum error correction scheme for a one-photon erasure lies well within present technological capabilities.

We construct a tridiagonal matrix representation for the three-dimensional Dirac-Coulomb Hamiltonian that provides for a simple and straightforward relativistic extension of the complex scaling method. Besides the Coulomb interaction, additional vector, scalar, and pseudoscalar coupling to short-range potentials are also included in the same representation. Using that, we are able to obtain highly accurate values for the relativistic bound states and resonance energies. A simple program code is developed to perform the calculation for a given charge, angular momentum, and potential configuration. The resonance structure in the complex relativistic energy plane is also shown graphically. Illustrative examples are given and we verify that in the nonrelativistic limit one obtains known results. As an additional advantage of this tridiagonal representation, we use it to obtain highly accurate evaluation of the relativistic bound state energies for the Woods-Saxon potential (as a model of nuclear interaction) with the nucleus treated as a solid sphere of uniform charge distribution.

Autoionization dynamics of core-valence doubly excited states in ${\mathrm{N}}_2$ is studied by measuring angular dependence and photon energy evolution of inner-shell photoelectron spectra. The anisotropic electron emissions in the autoionization are interpreted in terms of symmetries of the doubly excited states. The autoionization features in the photoelectron spectra demonstrate clearly the electronic decay closely related to nuclear dynamics in the femtosecond regime. A nonadiabatic picture is required to describe the autoionization of a Rydberg-type doubly excited state.

We study the quantum dynamics of a material wave packet bouncing off a modulated atomic mirror in the presence of a gravitational field. We find the occurrence of coherent accelerated dynamics for atoms beyond the familiar regime of dynamical localization. The acceleration takes place for certain initial phase-space data and within specific windows of modulation strengths. The realization of the proposed acceleration scheme is within the range of present-day experimental possibilities.