We show that the technique of Stark-chirped rapid adiabatic passage (SCRAP), hitherto used for complete population transfer between two quantum states, offers a simple and robust method for complete population transfer amongst three states in atoms and molecules. In this case SCRAP uses three laser pulses: a strong far-off-resonant pulse modifies the transition frequencies by inducing dynamic Stark shifts and thereby creating time-dependent level crossings amongst the three diabatic states, while near-resonant and moderately strong pump and Stokes pulses, appropriately offset in time, drive the population between the initial and final states via adiabatic passage. The population transfer efficiency is robust to variations in the intensities of the lasers, as long as these intensities are sufficiently large to enforce adiabatic evolution. With suitable pulse timings the population in the (possibly decaying) intermediate state can be minimized, as with stimulated Raman adiabatic passage (STIRAP). This technique applies to one-photon as well as multiphoton transitions and it is also applicable to media exhibiting inhomogeneous broadening; these features represent clear advantages over STIRAP by overcoming the inevitable dynamical Stark shifts that accompany multiphoton transitions as well as unwanted detunings, e.g., induced by Doppler shifts.

We analyze the physics of Bose-Einstein condensates confined in two dimensional (2D) quasiperiodic optical lattices, which offer an intermediate situation between ordered and disordered systems. First, we analyze the time-of-flight interference pattern that reveals quasiperiodic long-range order. Second, we demonstrate localization effects associated with quasidisorder as well as quasiperiodic Bloch oscillations associated with the extended nature of the wave function of a Bose-Einstein condensate in an optical quasicrystal. In addition, we discuss in detail the crossover between diffusive and localized regimes when the quasiperiodic potential is switched on, as well as the effects of interactions.

Saturated tabletop lasers operating at $5\mathrm{Hz}$ repetition rate with average powers $>1\mu \mathrm{W}$ were demonstrated at wavelengths between 16.5 and $13.9\mathrm{nm}$ in the $4d{}^{1}S_0–4p{}^{1}P_1$ transitions of Ni-like ions. The results were obtained using picosecond laser heating pulses with an energy of only $1\mathrm{J}$ by optimizing the angle of incidence for maximum energy deposition. Lasing was also observed for shorter wavelength transitions of the same isoelectronic sequence, with amplification in the $11.9\mathrm{nm}$ line of Ni-like Sn approaching gain saturation, and progressively reduced gain for wavelengths as low as $10.9\mathrm{nm}$ for Ni-like Te. These high repetition rate soft x-ray lasers will enable new applications in science and the development of unique metrology and processing tools for industry.

We present our recently developed random-phase approximation with exchange (RPAE) method, which can be used to study the inner-shell electron transition in an open-shell atom. The expressions for the matrix elements of all terms of the dipole and Coulomb interactions have been derived and implemented in a computer program. The photoionization cross sections of the $4d$ giant resonances of ${\mathrm{Xe}}^{+}$, I, and ${\mathrm{I}}^{+}$ have been calculated. The results for ${\mathrm{Xe}}^{+}$ and ${\mathrm{I}}^{+}$ agree very well with the experimental data. However, the theoretical results for the I $4d$ cross section are still almost three to four times higher than the experimental data. We recommend a remeasurement of the I $4d$ giant resonance with a careful experimental arrangement.

We present experimental evidence for a strong dependence on the angle between the molecular axis of ${\mathrm{H}}_2$ and the direction of the incoming projectile $\left(p\right)$ in the cross section for transfer excitation in fast $p\text{−}{\mathrm{H}}_2$ collisions. For collision energies of 1.0 and $1.3\mathrm{MeV}$ we find good agreement between the observed data and an analytical expression based on a two-atomic-center description using Brinkman-Kramers amplitudes. This clearly shows that the observed angular dependence is a result of quantum mechanical interference and not a trivial geometrical effect.

We address a problem of identifying a given pure state with one of two reference pure states, when no classical knowledge on the reference states is given, but a certain number of copies of them are available. We assume the input state is guaranteed to be either one of the two reference states. This problem, which we call quantum pure state identification, is a natural generalization of the standard state discrimination problem. The two reference states are assumed to be independently distributed in a unitary invariant way in the whole state space. We give a complete solution for the averaged maximal success probability of this problem for an arbitrary number of copies of the reference states in general dimension. It is explicitly shown that the obtained mean identification probability approaches the mean discrimination probability as the number of the reference copies goes to infinity.

We address the problem of springlike coupling between bosons in an open-chain configuration where the counter-rotating terms are explicitly included. We show that fruitful insight can be gained by decomposing the time-evolution operator of this problem into a pattern of linear-optics elements. This allows us to provide a clear picture of the effects of the counter-rotating terms in the important problem of long-haul entanglement distribution. The analytic control over the variance matrix of the state of the bosonic register allows us to track the dynamics of the entanglement. This helps in designing a global addressing scheme, complemented by a proper initialization of the register, which quantitatively improves the entanglement between the extremal oscillators in the chain, thus providing a strategy for feasible long-distance entanglement distribution.

The Casimir interaction between two media of ground-state atoms is well described with the help of the Lifshitz formula depending upon the permittivity of the media. We will show that this formula is in contradiction with experimental evidence for excited atoms. We calculate the Casimir force between two atoms if one or both of them are excited. We use methods of quantum electrodynamics specially derived for the problem. It enables us to take into account the excited-state radiation widths of atoms. Then we calculate the force between the excited atom and medium of ground-state atoms. The results are in agreement with the ones obtained by other authors who used perturbation theory or linear response theory. Generalization of our results to the case of the interaction between two media of excited atoms results in a formula, which is in not only in quantitative, but in qualitative contradiction with the Lifshitz formula. This contradiction disappears if the media of ground-state atoms are considered. Moreover, our result does not include the permittivity of the media. It includes a quantity which differs from the permittivity only for excited atoms. The main features of our results are as follows. The interaction is resonant, the force may be either attractive or repulsive depending on the resonant frequencies of the atoms of different media, and the value of the Casimir force may be several orders of magnitude lager than that predicted by the Lifshitz formula. The features mentioned here are in agreement with known experimental and theoretical evidence obtained by many authors for the interaction of a single excited atom with dielectric media.

By adding any complex absorbing potential (CAP) $-i\lambda V\left(\vec{r}\right)$ to a system Hamiltonian, the corresponding complex eigenvalues are analytical functions of $\lambda ,E_j\left(\lambda \right)$. It is shown here that for a quite general flexible class of CAP’s the real part of ${\lim }_{\lambda \to 0}{E}_j\left(\lambda \right)$ provides the resonance energy. The imaginary part of that limit is the resonance width (i.e., inverse lifetime) in spite of the fact that $\mathrm{Im}{E}_j\left(0\right)=0$. The need for the Padé approximation within this approach is explained. Application to an illustrative numerical test case model Hamiltonian is given. This method could open a gate for studying systems that could not be studied until now due to the complexity of the numerical computations. In particular, one may in this way obtain resonance energies by a modification, in a straightforward simple manner, of the widely used conventional methods that were developed for the calculations of bound states.

We consider the entanglement of orthogonal generalized Bernoulli states in two separate single-mode high-$Q$ cavities. The expectation values and the correlations of the electric field in the cavities are obtained. We then define, in each cavity, a dichotomic operator expressible in terms of the field states which can be, in principle, experimentally measured by a probe atom that “reads” the field. Using the quantum correlations of couples of these operators, we construct a Bell’s inequality which is shown to be violated for a wide range of the degree of entanglement and which can be tested in a simple way. Thus the cavity fields directly show quantum nonlocal properties. A scheme is also sketched to generate entangled orthogonal generalized Bernoulli states in the two separate cavities.

Interactions among qubits are essential for performing two-qubit quantum logic operations. However, nature gives us only nearest neighbor interactions in simple and controllable settings. Here we propose a strategy to induce interactions among two atomic entities that are not necessarily neighbors of each other through their common coupling with a cavity field. This facilitates fast multiqubit quantum logic operations through a set of two-qubit operations. Using its explicit position dependence, this interaction can be employed for simulation of quantum spin systems. The ideas presented here are applicable to various quantum-information proposals for atom-based qubits such as trapped ions, atoms trapped in optical cavities, and optical lattices.

We find exact solutions for a universal set of quantum gates on a scalable candidate for quantum computers, namely an array of two-level systems. The gates are constructed by a combination of dynamical and geometrical (non-Abelian) phases. Previously these gates have been constructed mostly on nonscalable systems and by numerical searches among the loops in the manifold of control parameters of the Hamiltonian.

X-ray-absorption and x-ray Raman scattering spectra recorded in the vicinity of the manganese $L_{2,3}$ absorption edge in $\mathrm{Mn}{\mathrm{F}}_2$ are presented. The results are compared with free-ion Hartree-Fock calculations for ${\mathrm{Mn}}^{2+}$. We confirm that x-ray-absorption and valence emission spectra of $\mathrm{Mn}{\mathrm{F}}_2$ can be explained almost entirely in terms of the ${\mathrm{Mn}}^{2+}$ free ion, with the resonant valence emission providing detailed information about the $d^5$ electronic structure. We found that at the $L_3$ absorption edge elastic emission is dominant, while at the $L_2$ valence emission is dominated by a feature corresponding to a transition into a low-spin state in the ground configuration, with other emission satellites corresponding to energy losses as large as $10\mathrm{eV}$. The measured energies of these low spin states are in good agreement, with the ${\mathrm{Mn}}^{2+}$ free ion calculation.

We have performed calculations of two successive charge transfers from Rydberg states in a strong magnetic field. In the first charge transfer, a positron interacts with a highly excited atom to form positronium. In the second stage, the positronium interacts with an antiproton to give antihydrogen. For many parameters, our results are in qualitative agreement with previous calculations with no magnetic field. However, we do find that there are important changes which may affect the usefulness of the method for efficient formation of antihydrogen that can be trapped.

We have calculated the electronic stopping power and the energy-loss straggling parameter of swift He, Li, B, and N ions moving through several oxides, namely $\mathrm{Si}{\mathrm{O}}_2$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, and $\mathrm{Zr}{\mathrm{O}}_2$. The evaluation of these stopping magnitudes was done in the framework of the dielectric formalism. The target properties are described by means of a combination of Mermin-type energy-loss functions that characterize the response of valence-band electrons, together with generalized oscillator strengths to take into account the ionization of inner-shell electrons. We have considered the different charge states that the projectile can have, as a result of electron capture and loss processes, during its motion through the target. The electron density for each charge state was described using the Brandt-Kitagawa statistical model and, for He and Li ions, also hydrogenic orbitals. This procedure provides a realistic representation of both the excitation properties of the target electrons and the projectile charge density, yielding stopping powers that compare reasonably well with available experimental data above a few tens of keV/amu.

A robust and versatile method is demonstrated to maintain, for an arbitrary time, quasiconstant and strong orientation for molecules with minute dipole moments. The procedure is based on submitting molecules in cyclic wave packets to periodic trains of nonresonant pulses in an electrostatic field. We show that approximate cyclic states can be created by suddenly switching off a long laser pulse. A control scheme to remove the static field without spoiling orientation is suggested, which would permit large field-free orientation between pulses.

We have investigated the noise-induced transition of cold atoms between double or triple phase-space attractors that are produced in the parametrically driven magneto-optical trap. The transition rates between two dynamic attractors, directly measured for various modulation frequencies and amplitudes, are in good agreement with calculations from the dynamic version of Kramers’ theory and Monte Carlo simulations. For the triple attractors, the transition rates are measured indirectly through the steady-state population and the results are also in agreement with simulations. Our experiment may be useful for study of nonlinear dynamic problems involving transitions between states far from equilibrium.

We have performed experiments using a three-dimensional Bose-Einstein condensate of sodium atoms in a one-dimensional optical lattice to explore some unusual properties of band structure. In particular, we investigate the loading of a condensate into a moving lattice and find nonintuitive behavior. We also revisit the behavior of atoms, prepared in a single quasimomentum state, in an accelerating lattice. We generalize this study to a cloud whose atoms have a large quasimomentum spread, and show that the cloud behaves differently from atoms in a single Bloch state. Finally, we compare our findings with recent experiments performed with fermions in an optical lattice.

We analyze theoretically the experiment reported in [F. Gerbier et al., Phys. Rev. Lett. 95, 050404 (2005)]. There, the interference pattern produced by an expanding atomic cloud in the Mott insulator regime was observed, indicative of short-range coherence in the system. The latter was traced back to the presence of a small amount of particle-hole pairs in the insulating phase for finite lattice depths. We analyze the influence of these pairs on the interference pattern using a random phase approximation, and derive the corresponding visibility. We also account for the inhomogeneity inherent to atom traps in a local density approximation. The calculations reproduce the experimental observations, except for very large lattice depths. The deviation from the measurement in this range is attributed to the increasing importance of nonadiabatic effects.

We show that an optical parametric oscillator based on three concurrent ${\chi }^{\left(2\right)}$ nonlinearities can produce, above threshold, bright output beams of macroscopic intensities which exhibit strong tripartite continuous-variable entanglement. We also show that there are two ways that the system can exhibit a three-mode form of the Einstein-Podolsky-Rosen paradox, and calculate the extracavity fluctuation spectra that may be measured to verify our predictions.