The results of a theoretical study of HOCO${}^{-}$ photodetachment are presented with a view toward understanding the origin of two peaks observed by Lu and Continetti [Phys. Rev. Lett. 99, 113005 (2007)] in the photoelectron kinetic energy spectrum very close to threshold. It is shown that the peaks can be attributed to vibrational Feshbach resonances of dipole-bound trans-HOCO${}^{-}$, and not $s$- and $p$-wave shape resonances as previously assumed. Fixed-nuclei variational electron-HOCO scattering calculations are used to compute photodetachment cross sections and laboratory-frame photoelectron angular distributions. The calculations show a broad $A$${}^{\text{'}\text{'}}$($\pi$*)-shape resonance several electron volts above threshold.

We study the theory of several aspects of the dynamics of coherent atom-molecule conversion in spin-one Bose-Einstein condensates. Specifically, we discuss how, for a suitable dark-state condition, the interplay of spin-exchange collisions and photo association leads to the stable creation of an atom-molecule pair from three initial spin-zero atoms. This process involves two two-body interactions and can be intuitively viewed as an effective three-body recombination. We investigate the relative roles of photo association and of the initial magnetization in the “resonant” case, where the dark-state condition is perfectly satisfied. We also consider the “nonresonant” case, where that condition is satisfied either only approximately—the so-called adiabatic case—or not at all. In the adiabatic case, we derive an effective nonrigid pendulum model that allows one to conveniently discuss the onset of an antiferromagnetic instability in an “atom-molecule pendulum,” as well as large-amplitude pair oscillations and atom-molecule entanglement.

A common problem in Bell-type experiments is the well-known detection loophole: if the detection efficiencies are not perfect and if one simply postselects the conclusive events, one might observe a violation of a Bell inequality, even though a local model could have explained the experimental results. In this paper, we analyze the set of all postselected correlations that can be explained by a local model, and show that it forms a polytope, larger than the Bell local polytope. We characterize the facets of this postselected local polytope in the Clauser-Horne-Shimony-Holt scenario, where two parties have binary inputs and outcomes. Our approach gives interesting insights on the detection loophole problem.

The geometry of classical dynamics in coupled oscillators with SU(2) transformations is explored and found to be relevant to a family of continuous-transformation orbits between Lissajous and trochoidal curves. The quantum wave-packet coherent states are derived analytically to correspond exactly to the transformation geometry of classical dynamics. By using the quantum wave-packet coherent states derived herein, stationary coherent states are constructed and are shown to possess spatial patterns identical to the transformation geometry between Lissajous and trochoidal orbits.

We present an operational interpretation of quantum discord based on the quantum state merging protocol. Quantum discord is the markup in the cost of quantum communication in the process of quantum state merging, if one discards relevant prior information. Our interpretation has an intuitive explanation based on the strong subadditivity of von Neumann entropy. We use our result to provide operational interpretations of other quantities like the local purity and quantum deficit. Finally, we discuss in brief some instances where our interpretation is valid in the single-copy scenario.

Quantum discord quantifies nonclassical correlations beyond the standard classification of quantum states into entangled and unentangled. Although it has received considerable attention, it still lacks any precise interpretation in terms of some protocol in which quantum features are relevant. Here we give quantum discord its first information-theoretic operational meaning in terms of entanglement consumption in an extended quantum-state-merging protocol. We further relate the asymmetry of quantum discord with the performance imbalance in quantum state merging and dense coding.

An electron-beam ion trap (EBIT) is used to measure extreme ultraviolet spectra between 10 and 25 nm from highly charged ions of tungsten with an open $3d$ shell (W xlviii through W lvi). We found that almost all strong lines are due to the forbidden magnetic-dipole ($M1$) transitions within $3d^n$ ground configurations. A total of 37 previously unknown spectral lines are identified using detailed collisional-radiative (CR) modeling of the EBIT spectra. A level-merging scheme for compactification of rate equations is described. The CR simulations for Maxwellian plasmas show that several line ratios involving these $M1$ lines can be used to reliably diagnose temperature and density in hot fusion devices.

Hylleraas-configuration-interaction (Hy-CI) method variational calculations are reported for the ${}^{1}S$ ground state of neutral beryllium. The best nonrelativistic energy obtained was $-14.667\hspace{0.5em}356\hspace{0.5em}4$ hartree, which is estimated to be accurate to a tenth of a microhartree.

State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the (BaRb)${}^{+}$ molecular ion in the Born-Oppenheimer approximation for the singlet and triplet states dissociating into the ground-state ${}^1$$S$ Rb${}^{+}$ ion and the Ba atom in the ground ${}^1$$S$ state or the lowest singlet or triplet $d$ excited states, and for the singlet and triplet states dissociating into the ground-state ${}^2$$S$ Rb atom and the ground-state ${}^2$$S$ Ba${}^{+}$ ion. The ground-state potential energy was obtained with the coupled-cluster method restricted to single, double, and nonperturbative triple excitations. The first triplet states in the $\Sigma$, $\Pi$, and $\Delta$ symmetries were computed with the restricted open-shell coupled-cluster method restricted to single, double, and nonperturbative triple excitations. All other excited-state potential energy curves were computed using the equation of motion approach within the coupled-cluster singles, doubles, and linear triples framework. The long-range coefficients describing the electrostatic, induction, and dispersion interactions at large interatomic distances are also reported. The electric transition dipole moments governing the $x$ ${}^1\Sigma \to {}^1\Sigma ,{}^1\Pi$ transitions have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Nonadiabatic radial and angular coupling matrix elements as well as the spin-orbit coupling matrix elements have been evaluated using the multireference configuration-interaction method restricted to single and double excitations with a large active space. With these couplings, the spin-orbit-coupled (relativistic) potential energy curves for the 0${}^{+}$ and 1 states relevant for the running experiments have been obtained. Finally, relativistic transition moments and nonadiabatic coupling matrix elements were obtained from the nonrelativistic results and spin-orbit eigenvectors. The electronic structure input has been employed in the single-channel scattering calculations of the collisional cross sections between the Ba${}^{+}$ ion and Rb atom. Both nonrelativistic and relativistic potentials were used in these calculations. Our results show that the inelastic cross section corresponding to the charge transfer from the Rb atom to the Ba${}^{+}$ ion is much smaller than the elastic one over a wide range of energies up to 1 mK. This suggests that sympathetic cooling of the Ba${}^{+}$ ion by collisions with ultracold Rb atoms should be possible.

The effects of Coulomb interaction screening on electron-hydrogen atom 1$S$ → 2$S$ and 1$S$ → 2$p$ excitation scattering between the $n$ = 2 and $n$ = 3 excitation thresholds have been investigated by using the $R$-matrix method with pseudostates. The excitation collision strengths show dramatic changes when the interaction screening length $D$ varies from ∞ to 9 a.u., as a result of the convergence of $S$-type and some $p$- and $D$-type Feshbach resonances to the varying 3$S$ or 3$p$ thresholds, and due to the crossover of some other $p$-, $D$- and all $F$-type Feshbach resonances into shape-type resonances when they pass across the 3$S$ or 3$p$ threshold at certain critical values of $D$. The noncrossover of some $p$- and $D$-type Feshbach resonances into shape-type resonances at the 3$S$ (or 3$p$ for those of $D$-type) threshold is at variance with the behavior of these types of resonances at the 2$S$ (2$p$ for those of D-type) threshold, which results from the threefold splitting of the $n$ = 3 hydrogenic level and, consequently, the more complex nature of the configuration mixing in the $n$ = 3 threshold region. The evolution of the total 1$S$ → 2$S$, 1$S$ → 2$p$, and 2$S$ → 2$p$ excitation collision strengths, when the screening strength varies, is presented and discussed.

The excited state dynamics of $o$-dichlorobenzene has been studied by femtosecond time-resolved photoelectron imaging. The lifetime of the first excited state $S_1$ of $o$-dichlorobenzene was determined to be 482 ± 10 ps. Field-free nonadiabatic alignment of the $o$-dichlorobenzene on the first excited state $S_1$ (with an asymmetry parameter k $=$ 0.153) by a femtosecond laser pulse was observed via time-resolved photoelectron angular distributions. Rotational wave packet revivals on the $S_1$ state of the typical asymmetric molecule $o$-dichlorobenzene at 296 ps has been measured.

We expand the existing polaron response theory, expressed within the Mori-Zwanzig projection operator formalism applicable for the transfer of arbitrary energy and zero momentum, for the case of finite momentum exchange. A general formula is then derived that can be used to calculate the response of a system to a probe that transfers both momentum and energy to the system. The main extension of the existing polaron response theory is the finite momentum exchange, which was not needed until now, since it is negligible for optical absorption. However, this formalism is needed to calculate the response of the polaronic system consisting of an impurity in a Bose-Einstein condensate (BEC) to Bragg spectroscopy. We show that the well-known features that appear in the optical absorption of the solid-state Fröhlich polaron are also present in the Bragg response of the BEC-impurity polaron. The f-sum rule is written in a form suitable to provide an independent consistency test for our results. The effect of lifetime broadening on the BEC-impurity spectrum is examined. The results derived here are discussed in the framework of an experimental realization consisting of a lithium impurity in a sodium condensate.

We demonstrate both theoretically and experimentally that a nonlinear beam can be reflected by a negative defect in a photonic lattice if the incident angle is below a threshold value. Above this threshold angle, the beam simply passes through the defect. This phenomenon occurs in both one- and two-dimensional photonic lattices, and it provides a way to use the incident angle to control beam propagation in a lattice network. If the defect is absent or positive, no evident transition from reflection to transmission occurs. These nonlinear phenomena are also compared with linear nondiffracting-beam propagation in a photonic lattice with a defect, and both similarities and differences are observed. In addition, some important features in linear and nonlinear beam propagations are explained analytically by using a linear model with a delta-function defect.

We experimentally study the spatial properties of the field generated by spontaneous parametric down-conversion (SPDC) when the pump laser beam is strongly focused in the nonlinear crystal. Special attention is paid to classical intensity measurements with a CCD camera. We introduce the concept of a classical equivalent source that replicates all the coherence properties of SPDC light and explains all our experimental results. We show that, in contrast with experiments with a well-collimated pump, here both the phase-matching conditions and the position of the focusing plane determine the measured intensity profiles in the image plane of the crystal. The transition from the near-field regime to the far field is investigated. Measurements of two-photon correlations under strong focusing are also presented and the special features thereof are discussed.

We consider the long-term evolution of a random nonlinear wave that propagates in a multimode optical waveguide. The optical wave exhibits a thermalization process characterized by an irreversible evolution toward an equilibrium state. The tails of the equilibrium distribution satisfy the property of energy equipartition among the modes of the waveguide. As a consequence of this thermalization, the optical field undergoes a process of classical wave condensation, which is characterized by a macroscopic occupation of the fundamental mode of the waveguide. Considering the nonlinear Schrödinger equation with a confining potential, we formulate a wave turbulence description of the random wave into the basis of the eigenmodes of the waveguide. The condensate amplitude is calculated analytically as a function of the wave energy, and it is found in quantitative agreement with the numerical simulations. The analysis reveals that the waveguide configuration introduces an effective physical frequency cutoff, which regularizes the ultraviolet catastrophe inherent to the ensemble of classical nonlinear waves. The numerical simulations have been performed in the framework of a readily accessible nonlinear fiber optics experiment.

Bound entangled states are the exotic objects in the entangled world. They require entanglement to create them, but once they are formed, it is not possible to locally distill any free entanglement from them. It is only until recently that a few bound entangled states were realized in the laboratory. Motivated by these experiments, we propose schemes for creating various classes of bound entangled states with photon polarization. These include Acín-Bruß-Lewenstein-Sanpara states, Dür’s states, Lee-Lee-Kim bound entangled states, and an unextendible-product-basis bound entangled state.

Shortcomings of experimental techniques are usually assumed to diminish nonclassical properties of quantum systems. Here it is demonstrated that this standard assumption is not true in general. It is theoretically shown that the inability to resolve different photon numbers with photodetection may pseudoincrease a measured Bell parameter. Under proper conditions one even pseudoviolates the quantum Cirel’son bound of the Bell parameter, and the corresponding density operator fails to be positive semidefinite. This paradox can be resolved by appropriate squash models.

We develop criteria to detect three classes of nonlocality that have been shown by Wiseman et al. [Phys. Rev. Lett. 98, 140402 (2007)] to be nonequivalent: entanglement, EPR steering, and the failure of local hidden-variable theories. We use the approach of Cavalcanti et al. [Phys. Rev. Lett. 99, 210405 (2007)] for continuous variables to develop the nonlocality criteria for arbitrary spin observables defined on a discrete Hilbert space. The criteria thus apply to multisite qudits, i.e., systems of fixed dimension $d$, and take the form of inequalities. We find that the spin moment inequalities that test local hidden variables (Bell inequalities) can be violated for arbitrary $d$ by optimized highly correlated nonmaximally entangled states provided the number of sites $N$ is high enough. On the other hand, the spin inequalities for entanglement are violated and thus detect entanglement for such states, for arbitrary $d$ and $N$, and with a violation that increases with $N$. We show that one of the moment entanglement inequalities can detect the entanglement of an arbitrary generalized multipartite Greenberger-Horne-Zeilinger state. Because they involve the natural observables for atomic systems, the relevant spin-operator correlations should be readily observable in trapped ultracold atomic gases and ion traps.

It is shown that a weak measurement of a quantum system produces a new state of the quantum system which depends on the prior state, as well as the (uncontrollable) measured position of the pointer variable of the weak-measurement apparatus. The result imposes a constraint on hidden-variable theories which assign a different state to a quantum system than standard quantum mechanics. The constraint means that a crypto-nonlocal hidden-variable theory can be ruled out in a more direct way than previously done.

The dissipative quantum dynamics of a two-level system interacting with a structured reservoir consisting of a damped harmonic mode is investigated by means of the numerically exact path integral Monte Carlo method. This approach provides benchmark results in a broad range of parameter space, in particular, in those domains which are not accessible by approximate methods and alternative numerical schemes, that is, strong coupling between system and harmonic mode and from low to high temperatures. For low temperatures the numerical data are quantitatively in agreement with the noninteracting blip approximation only in the regimes of very weak and very strong coupling. It turns out that the entangled dynamics of the two-level system and the harmonic mode is relatively robust so that its signatures are observable up to relatively strong friction and high temperatures. Nonequilibrium initial preparations of the reservoir with respect to the initial state of the system give rise, for strong interactions, to a stepwise decay of the population, thus displaying coherent dynamics of the bath. The impact of an additional Ohmic bath coupled directly to the two-level system is studied as well, including the case where both reservoirs carry different temperatures.