The inner-shell photoexcitation of the Rydberg series of Be atoms is explored from both experimental and theoretical points of view. We used synchrotron radiation to photoionize Be atoms and the time-of-flight method to record charge-separated photoion yield spectra. Many new autoionizing resonance peaks were observed in the ${\mathrm{Be}}^{2+}$ and ${\mathrm{Be}}^{+}$ spectra. They were categorized as Rydberg series members converging to the $1s\left(2s2p{}^{1}P^o\right){}^{2}P^o$, $1s\left(2s3s{}^{3}S\right){}^{2}S$, and $1s\left(2s3s{}^{1}S\right){}^{2}S$ series limits. Furthermore, numerical calculations using multiconfiguration Dirac-Fock (MCDF) method enabled us to assign unknown resonance peaks as the $1s\left(2s3p{}^{3}P^o\right){}^{2}P^{o}ns$ series members. The calculation of the ground state of Be atoms revealed that the admixture of the $1s^{2}2p^2$ into the ground state amounts to 8.67%.

A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional trap can be described with the lowest Landau-level set of states. In this case, the condensate wave function $\psi (x,y)$ is a Gaussian function of $r^2=x^2+y^2$, multiplied by an analytic function $P\left(z\right)$ of the single complex variable $z=x+iy$; the zeros of $P\left(z\right)$ denote the positions of the vortices. Here, a similar description is used for a rapidly rotating anisotropic two-dimensional trap with arbitrary anisotropy $({\omega }_x∕{\omega }_y⩽1)$. The corresponding condensate wave function $\psi (x,y)$ has the form of a complex anisotropic Gaussian with a phase proportional to $xy$, multiplied by an analytic function $P\left(\zeta \right)$, where $\zeta \propto x+i{\beta }_{-}y$ and $0⩽{\beta }_{-}⩽1$ is a real parameter that depends on the trap anisotropy and the rotation frequency. The zeros of $P\left(\zeta \right)$ again fix the locations of the vortices. Within the set of lowest Landau-level states at zero temperature, an anisotropic parabolic density profile provides an absolute minimum for the energy, with the vortex density decreasing slowly and anisotropically away from the trap center.

A procedure is developed which allows one to measure all the parameters occurring in a complete model [A. A. Semenov et al., Phys. Rev. A 74, 033803 (2006)] of realistic leaky cavities with unwanted noise. The method is based on the reflection of properly chosen test pulses by the cavity.

We report on a large scale calculation concerning the $5s^2{}^{1}S$ and $5s5p{}^{1,3}P$ levels in ${}^{88}\mathrm{Sr}\mathrm{I}$, using multiconfiguration Dirac-Fock methods. Our focus is on the ${}^{3}P_2$ meta-stable level, which has been shown to be extremely useful in atom cooling and trapping experiments. The lifetime for this level from our work $\left(1071s\right)$ agrees very well with a previous theoretical value, but not with the available experimental value $\left({520}_{-140}^{+310}s\right)$. The results for all the transitions between the $5s^2{}^{1}S$ and $5s5p{}^{1,3}P$ levels and within the $5s5p{}^{1,3}P$ terms are also given.

The hydrogen Lyman-$\alpha$, Balmer-$\alpha$, and Balmer-$\beta$ emission has been measured from the ${\mathrm{H}}_2\mathrm{O}$ molecule at photon energies exceeding the $1s$ ionization threshold. Fluorescence emission is shown to be a sensitive probe to neutral core-hole doubly excited states and singly ionized $1s$ shake-up states that are embedded in the core ionization continuum. In addition, the photoabsorption spectrum of the water molecule in the energy range of the double excitations has been measured with better statistics than previously.

While exact cloning of an unknown quantum state is prohibited by the linearity of quantum mechanics, approximate cloning is possible and has been used, e.g., to derive limits on the security of quantum communication protocols. In the case of asymmetric cloning, the information from the input state is distributed asymmetrically between the different output states. Here, we consider asymmetric phase-covariant cloning, where the goal is to optimally transfer the phase information from a single input qubit to different output qubits. We construct an optimal quantum cloning machine for two qubits that does not require ancilla qubits and implement it on an NMR quantum information processor.

We propose a scheme to implement the two-qubit gates between the nuclear spins of the encapsulated atoms in endohedral fullerenes ${}^{15}\mathrm{N}@{\mathrm{C}}_{60}$ or ${}^{31}\mathrm{P}@{\mathrm{C}}_{60}$, within today’s magnetic resonance techniques. Since there is no interaction between the nuclear spins, this scheme employs the electronic spins as medium and two swap operations are proposed to transfer the information between the nuclear spin $\frac{1}{2}$ and the electronic spin $\frac{3}{2}$, and between two electronic spins $\frac{3}{2}$. These two-qubit gates, along with the single-qubit rotation gates, compose a universal set of quantum gates in fullerene-based quantum computation.

A detailed investigation of the long-lived states of the hydrogen molecule anion has been performed within the ab initio–based nonlocal resonance model. The resonances in the $X{}^2\Sigma _u^{+}$ electronic state of $\mathrm{H}_2{}^{-}$ are stabilized against autodetachment by molecular rotation and can be interpreted as orbiting states of $\mathrm{H}+{\mathrm{H}}^{-}$ with high angular momenta $(J=22-27)$. The lifetimes and energies of all long-lived states have been calculated for the hydrogen molecular anion and its isotopic analogs. Recent experimental values of Heber et al. [Phys. Rev. A 73, 060501(R) (2006)] for lifetimes of $\mathrm{H}_2{}^{-}$, $\mathrm{H}{\mathrm{D}}^{-}$, and $\mathrm{D}_2{}^{-}$ can be explained within the model. For $\mathrm{T}_2{}^{-}$, we predict a large number of states with lifetimes up to $\sim 0.1\mathrm{s}$.

The alignment of nuclear states resonantly formed in nuclear excitation by electron capture (NEEC) is studied by means of a density matrix technique. The vibrational excitations of the nucleus are described by a collective model and the electrons are treated in a relativistic framework. Formulas for the angular distribution of photons emitted in the nuclear relaxation are derived. We present numerical results for alignment parameters and photon angular distributions for a number of heavy elements in the case of $E2$ nuclear transitions. Our results are intended to help future experimental attempts to discern NEEC from radiative recombination, which is the dominant competing process.

When a quantum transition is followed by a classical process, as in strong-field rescattering events, it is essential to recognize the different time scales appropriate to each process. This establishes the sequential nature of the phenomena, and the necessity of satisfying quantum and classical conservation conditions independently. The term “rescattering” has been used in both quantum and classical senses, and the distinction is important. An example is examined where proper care has not been taken in distinguishing between quantum and classical conditions. The result is a major violation of angular momentum conservation that has apparently been unrecognized. An explanation for how this could happen is provided. Application of the principles presented here is important for current proposals to alter the parameters of laser focusing in efforts to overcome relativistic effects that degrade higher harmonic generation. In the (extreme ultraviolet) XUV and x-ray environments, the quantum-classical time distinction is blurred, leading to a loss of the simplifying features of classical behavior.

The time evolution of Stark wave packets in Rydberg atoms under the influence of colored noise is analyzed. The Stark wave packets are generated by exposing $K\left(350p\right)$ Rydberg atoms to an electric field step. Their time evolution is monitored using a half-cycle probe pulse that is applied after a variable time delay. The noise is generated by randomly modulating the amplitude of the static field. We show that noise results in an enhanced and irreversible dephasing of Stark quantum beats, as monitored by the damping of the beat amplitude. This source of decoherence is most effective when the characteristic frequency of the noise power spectrum matches the orbital frequency of the Rydberg electron. Noise driven resonant $\Delta n=1$ transitions broaden the energy distribution thereby accelerating the dephasing.

We discuss the fabrication and characterization of fiber Fabry-Perot cavities developed for integrated atom detection on the atom chip. Investigations show that the cavities are suitable for the detection of small numbers of atoms, with restrictions due to absorption in the Bragg gratings. We show that a significant reduction in these absorption losses can be attained by thermal annealing, removing any material limitations to single-atom detection.

We study on-site occupation number fluctuations in a system of interacting bosons in an optical lattice. The ground-state distribution is obtained analytically in the limiting cases of strong and weak interaction, and by means of exact Monte Carlo simulations in the strongly correlated regime. As the interaction is increased, the distribution evolves from Poissonian in the noninteracting gas to a sharply peaked distribution in the Mott-insulator (MI) regime. In the special case of large occupation numbers, we demonstrate analytically and check numerically that there exists a wide interval of interaction strength, in which the on-site number fluctuations remain Gaussian and are gradually squeezed until they are of order unity near the superfluid (SF)-MI transition. Recently, the on-site number statistics were studied experimentally in a wide range of lattice potential depths [Phys. Rev. Lett. 96, 090401 (2006)]. In our simulations, we are able to directly reproduce experimental conditions using temperature as the only free parameter. Pronounced temperature dependence suggests that measurements of on-site atom number fluctuations can be employed as a reliable method of thermometry in both SF and MI regimes.

A spin-dependent localized Hartree-Fock density-functional approach is presented for the efficient and accurate treatment of inner-shell excited states of atomic systems. The approach is applied to the calculation of the total and excitation energies of inner-shell excited states of several closed-shell atomic systems: Be, ${\mathrm{B}}^{+}$, Ne, and Mg. The predicted results are in overall good agreement with available experimental and other ab initio theoretical data. In addition, results for highly excited inner-shell states are presented.

We predict stable, collapse-free solitonslike structures in two-dimensional nonlinear Schrödinger systems in subdiffractive regimes, accomplished by a spatiotemporal modulation of the external potential. We investigate the scaling laws, the stability, and the dynamical properties of these subdiffractive solitons.

We apply the techniques introduced by Kraus et al. [Phys. Rev. Lett. 95, 080501 (2005)] to prove security of quantum-key-distribution (QKD) schemes using two-way classical post-processing as well as QKD schemes based on weak coherent pulses instead of single-photon pulses. As a result, we obtain improved bounds on the secret-key rate of these schemes. For instance, for the six-state protocol using two-way classical post-processing we recover the known threshold for the maximum tolerated bit error rate of the channel, 0.276, but demonstrate that the secret-key rate can be substantially higher than previously shown. Moreover, we provide a detailed analysis of the Bennett-Brassard 1984 (BB84) and the SARG protocol using weak coherent pulses (with and without decoy states) in the so-called untrusted-device scenario, where the adversary might influence the detector efficiencies. We evaluate lower bounds on the secret-key rate for realistic channel parameters and show that, for channels with low noise level, the bounds for the SARG protocol are superior to those for the BB84 protocol, whereas this advantage disappears with increasing noise level.

We present the results of calculations defining global, three-dimensional representations of the complex-valued potential-energy surfaces of the ${}^{2}B_1$, ${}^{2}A_1$, and ${}^{2}B_2$ metastable states of the water anion that underlie the physical process of dissociative electron attachment to water. The real part of the resonance energies is obtained from configuration-interaction calculations performed in a restricted Hilbert space, while the imaginary part of the energies (the widths) is derived from complex Kohn scattering calculations. A diabatization is performed on the ${}^{2}A_1$ and ${}^{2}B_2$ surfaces, due to the presence of a conical intersection between them. We discuss the implications that the shapes of the constructed potential-energy surfaces will have on the nuclear dynamics of dissociative electron attachment to ${\mathrm{H}}_2\mathrm{O}$.

We report the results of a first-principles study of dissociative electron attachment to ${\mathrm{H}}_2\mathrm{O}$. The cross sections were obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multiconfiguration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential-energy surfaces for the three (${}^{2}B_1$, ${}^{2}A_1$, and ${}^{2}B_2$) electronic Feshbach resonances involved in this process. These three metastable states of ${\mathrm{H}}_2{\mathrm{O}}^{-}$ undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the ${}^{2}B_1$ and ${}^{2}A_1$ states as well as the conical intersection between the ${}^{2}A_1$ and ${}^{2}B_2$ states into our treatment. The nuclear dynamics are inherently multidimensional and involve branching between different final product arrangements as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system.

Two different strong-laser-field-assisted atomic processes are considered: the laser-assisted electron-ion radiative recombination (LAR) and the laser-assisted electron-atom scattering (LAS). Assuming Gaussian space-time distribution of laser intensity in focus, we calculated the focal-averaged spectra for these processes. These spectra form plateaulike structures and are qualitatively similar to the spectra calculated for fixed intensity. The difference is that for the focal-averaged results, the plateaus are more inclined and the oscillatory structures are suppressed (or even absent). We also investigate the contribution of incoherent electron scattering off neighboring atoms (ions) to the LAR and LAS spectra. We suppose that an electron, after the scattering on an ionic target, may recombine with another ion (we call this process ISLAR—incoherent scattering followed by LAR). Analogously, the electron that scatters on an atom in the LAS process may scatter once more on another atom (this is the double scattering). In both cases, two targets are involved and the process is incoherent. The spectra that involve these incoherent processes are compared with the corresponding spectra for the coherent LAR and LAS processes, in which an additional act of scattering off the same target is included. If the density of atomic targets is high enough, the contribution of incoherent scattering can be larger than the contribution of coherent scattering. The spectra of ISLAR and double scattering exhibit a cutoff-like behavior, having much higher cutoff energies than that of LAR and LAS.

We propose and discuss methods for detecting quasimolecular complexes which are expected to form in strongly interacting optical lattice systems. Particular emphasis is placed on the detection of composite fermions forming in Bose-Fermi mixtures. We argue that, as an indirect indication of the composite fermions and a generic consequence of strong interactions, periodic correlations must appear in the atom shot noise of bosonic absorption images, similar to the bosonic Mott insulator [S. Fölling et al., Nature (London) 434, 481 (2005)]. The composites can also be detected directly and their quasimomentum distribution measured. This method—an extension of the technique of noise correlation interferometry [E. Altman et al., Phys. Rev. A 79, 013603 (2004)]—relies on measuring higher order correlations between the bosonic and fermionic shot noise in the absorption images. However, it fails above a certain number of the constituents due to a dramatic increase of uncorrelated noise.