Theoretical cross sections for the pressure broadening by hydrogen of rotational transitions of water are compared to the latest available measurements in the temperature range 65–220 K. A high-accuracy interaction potential is employed in a full close-coupling calculation. A good agreement with experiment is observed above $~80$ K, while the sharp drop observed experimentally at lower temperatures is not predicted by our calculations. Possible explanations for this discrepancy include the failure of the impact approximation and the possible role of ortho-to-para conversion of ${\mathrm{H}}_2$.

We now experimentally demonstrate a Y-shaped graph state with photons’ polarization and spatial modes as qubits. Based on this state and a linear-type graph state, we report on the experimental realization of two different Bell inequality tests, which represent higher violation than previous Bell tests.

Recently, a “counterfactual” quantum-key-distribution scheme was proposed by T.-G. Noh [Phys. Rev. Lett. 103, 230501 (2009)]. In this scheme, two legitimate distant peers may share secret keys even when the information carriers are not traveled in the quantum channel. We find that this protocol is equivalent to an entanglement distillation protocol. According to this equivalence, a strict security proof and the asymptotic key bit rate are both obtained when a perfect single-photon source is applied and a Trojan horse attack can be detected. We also find that the security of this scheme is strongly related to not only the bit error rate but also the yields of photons. And our security proof may shed light on the security of other two-way protocols.

Path-integral formalism is employed to study normal and lateral Casimir interactions in a system composed of a dispersive medium surrounded by two semi-infinite ideal conductors. The dispersive medium is modeled by a continuum of harmonic oscillators, and it is shown that for smooth conductors, the normal force at small distances in the presence of a dispersive medium coincides with the original Casimir force, while at large distances, it tends to the original form with a renormalized coefficient. The correction to the normal force because of the roughness on one of the conductors is calculated. When the inner surfaces of both conductors have roughness, the lateral Casimir interaction occurs because of translational symmetry breaking, which is studied. It is shown that both normal and lateral Casimir forces in the presence of a dispersive medium are weaker in comparison with the original one and are proportional to the roughness amplitude squared. The dependence of the normal and lateral interactions on the memory and strength of the dispersive medium is considered.

The atomic masses of the alkali-metal isotopes ${}^6\mathrm{Li},{}^{23}\mathrm{Na},{}^{39,41}\mathrm{K},{}^{85,87}\mathrm{Rb}$, and ${}^{133}\mathrm{Cs}$ have been obtained from measurements of cyclotron frequency ratios of pairs of ions simultaneously trapped in a Penning trap. The results, with one standard deviation uncertainty, are: $M({}^6\mathrm{Li})=6.015\hspace{0.5em}122\hspace{0.5em}887\hspace{0.5em}4(16)\mathrm{u},M({}^{23}\mathrm{Na})=22.989769\hspace{0.5em}282\hspace{0.5em}8(26)\mathrm{u},M({}^{39}\mathrm{K})=38.963\hspace{0.5em}706\hspace{0.5em}485\hspace{0.5em}6(52)\mathrm{u},M({}^{41}\mathrm{K})=40.961\hspace{0.5em}825\hspace{0.5em}257\hspace{0.5em}4(48)\mathrm{u},M({}^{85}\mathrm{Rb})=84.911\hspace{0.5em}789739(9)\mathrm{u},M({}^{87}\mathrm{Rb})=86.909\hspace{0.5em}180\hspace{0.5em}535(10)\mathrm{u}$, and $M({}^{133}\mathrm{Cs})=132.905\hspace{0.5em}451\hspace{0.5em}963(13)\mathrm{u}$. Our mass of ${}^6\mathrm{Li}$ yields an improved neutron separation energy for ${}^7\mathrm{Li}$ of 7251.1014(45) keV.

$K\alpha$-to-$K\beta$ x-ray intensity ratios of Ti and Co in pure metals and in alloys of Ti${}_x$Co${}_{1-x}$ ($x=0.7$, 0.6, 0.5, 0.4, and 0.3) have been measured for understanding the charge-transfer and delocalization phenomena in the Ti${}_x$Co${}_{1-x}$ alloys using the energy-dispersive x-ray fluorescence technique. The valence-electron structure of Ti and Co in the samples have been evaluated by the comparison of the measured $K\alpha$-to-$K\beta$ x-ray intensity ratios with the results of multiconfiguration Dirac-Fock calculations for various electron structures of these metals. Significant changes in the 3$d$ electron population (with respect to the pure metal) are observed for Ti and Co in different alloy compositions. Our analysis indicates that these changes can be explained by assuming the transfer of 3$d$ electrons from one element to the other element (charge transfer) and/or the rearrangement of electrons between 3$d$ and 4$s$,4$p$ states (delocalization) of the individual metal atoms.

The hyperfine structure and isotope shifts of the $3s^{2}3p^2\hspace{0.5em}{}^3{P}_2\to 3s3p^3\hspace{0.5em}{}^3{D}_3^o$ transition in silicon have been measured. The transition at 221.7 nm was studied by-laser induced fluorescence in an atomic Si beam. For ${}^{29}\mathrm{Si}$, the hyperfine $A$ constant for the $3s^{2}3p^2\hspace{0.5em}{}^3{P}_2$ level was determined to be $-160.1\pm 1.3$ MHz ($1\sigma$ error), and the $A$ constant for the $3s3p^3\hspace{0.5em}{}^3{D}_3^o$ level is $-532.9\pm 0.6$ MHz. The isotope shifts (relative to the abundant isotope ${}^{28}\mathrm{Si}$) of the transition were determined to be $1753.3\pm 1.1$ MHz for ${}^{29}\mathrm{Si}$ and $3359.9\pm 0.6$ MHz for ${}^{30}\mathrm{Si}$. This is an improvement by about two orders of magnitude over a previous isotope shift measurement. From these results we are able to predict the hyperfine structure and isotope shift of the radioactive ${}^{31}\mathrm{Si}$ atom, which is of interest in building a scalable quantum computer.

We have measured absolute cross sections for single, double, triple, and quadruple ionization of ${\mathrm{C}}_{60}$ in collisions with 3 MeV/u C, F, and Si projectile ions at various projectile charge states. The experiment was performed using the recoil-ion time-of-flight technique. Projectile charge state dependence of the ionization yields was compared mainly with a model based on the giant dipole plasmon resonance (GDPR). In some cases, the continuum-distorted-wave–eikonal-initial-state (CDW-EIS) model which is normally applied for ion-atom collisions was also used as a reference. An excellent qualitative agreement between the experimental data for single and double ionization and the GDPR model predictions was found for all projectile charge states.

We present measurements of the circular dichroism of optically pumped Rb vapor near the $D_1$ resonance line. Collisions with the buffer gases ${}^3\mathrm{He}$ and ${\mathrm{N}}_2$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples.

O $1s$, C $1s$, and S $2p$ core-valence double ionization electron spectra of the OCS molecule have been obtained experimentally by a time-of-flight photoelectron-photoelectron coincidence spectroscopy technique. In order to analyze and assign the spectral features observed, we present a protocol for computing core-valence ionization energies of such systems. The protocol is based on a restricted active space multiconfigurational self-consistent field (MCSCF) methodology with a freeze-relax procedure to guarantee a correct core-valence state root index without variational collapse. Corrections for extended dynamical correlation and core-core correlation, respectively, are made by multiconfigurational perturbation theory and by uncontracted basis set Møller-Plesset theory. Envisioning applications to larger molecules, a spin-restricted open-shell density functional method is also applied for the lowest core-valence energies. Furthermore, cross sections through a scheme for computing multiatom Auger transitions generating core-valence holes are presented. We find that the procedure outlined is capable of deriving the energy onset of core-valence ionization within a fraction of an eV and that assignments can be made of the most salient spectral features.

We study the spin dynamics of a spin-1 ferromagnetic Bose-Einstein condensate with magnetic dipole-dipole interaction (MDDI) based on the Gross-Pitaevskii and Bogoliubov theories. We find that various magnetic structures such as checkerboards and stripes emerge in the course of the dynamics due to the combined effects of spin-exchange interaction, MDDI, quadratic Zeeman and finite-size effects, and nonstationary initial conditions. However, the short-range magnetic order observed by the Berkeley group [Phys. Rev. Lett. 100, 170403 (2008)] is not fully reproduced in our calculations; the periodicity of the order differs by a factor of 3 and the checkerboard pattern eventually dissolves in the course of time. Possible reasons for the discrepancy are discussed.

We develop a theoretical model to investigate the Bragg diffraction of an elongated interacting Bose-Einstein condensate which is illuminated by a pair of laser beams. We find that the mean-field effect resulting from the atomic interaction plays an important role in modifying the atomic coherence. Our results show that both the repulsive and attractive interactions would dampen the momentum oscillation of the condensate; they establish surprisingly distinguishable equilibria for the atomic occupations among different diffraction orders. We also give an experimental proposal to observe this phenomenon.

We study two many-body systems of bosons interacting via an infinite three-body contact repulsion in a lattice: a pairs quasicondensate induced by correlated hopping and the discrete version of the Pfaffian wave function. We propose to experimentally realize systems characterized by such interaction by means of a proper spin-1 lattice Hamiltonian: spin degrees of freedom are locally mapped into occupation numbers of emerging bosons, in a fashion similar to spin-1/2 and hardcore bosons. Such a system can be realized with ultracold spin-1 atoms in a Mott insulator with a filling factor of 1. The high versatility of these setups allows us to engineer spin-hopping operators breaking the SU(2) symmetry, as needed to approximate interesting bosonic Hamiltonians with three-body hardcore constraint. For this purpose we combine bichromatic spin-independent superlattices and Raman transitions to induce a different hopping rate for each spin orientation. Finally, we illustrate how our setup could be used to experimentally realize the first setup, that is, the transition to a pairs quasicondensed phase of the emerging bosons. We also report on a route toward the realization of a discrete bosonic Pfaffian wave function and list some open problems for reaching this goal.

A scheme for complex-valued acquisition of the diffraction imaging with quasimonochromatic incoherent light is theoretically proposed. The main idea is to project the real and the imaginary parts of a Fraunhofer diffraction field on intensity distributions, respectively, with the use of a $\pi /2$ phase-changing plate. The whole procedure is iterative algorithm free and needs no a priori knowledge of an arbitrary object. A numerical experiment and a quantitative confirmation are also given. To our knowledge, it was the first physical proposal for the complex-valued acquisition of a diffraction imaging by two-dimensional coherent patterns with thermal illumination.

We propose a method for enhancing the flatness of a supercontinuum centered at 1.55 $\mu$m by the use of specially designed tapered microstructured optical fibers (MOFs). Based on the procedure presented one can determine the linear taper profile parameters and the optimum launching conditions needed to achieve the broadest supercontinuum spectra (SC) and the best spectra flatness. We quantify the maximally broad and flat SC using the calculated standard deviation of the spectra at the required wavelength range and show that it is possible to obtain significantly better results than those obtained by using an untapered fiber.

Experimental data on total- and partial-ionization cross sections of ionic fragments of ${\mathrm{CO}}_2$ molecule produced by impact of 10–26-keV electrons are obtained on a crossed-beam apparatus in our laboratory. An ejected electron-produced ion-coincidence technique is employed together with a time-of-flight mass spectrometer for analysis of the ions. The six ionic fragments, ${\mathrm{CO}}_2{}^{+}$, ${\mathrm{CO}}^{+}$, ${\mathrm{CO}}_2{}^{2+}$, ${\mathrm{O}}^{+}$, ${\mathrm{C}}^{+}$, and ${\mathrm{C}}^{2+}$, resulting from dissociative ionization of the ${\mathrm{CO}}_2$ molecule are observed and identified; their relative ionization cross sections and branching ratios are determined as a function of impact energy. The binary-encounter Bethe model is found to overestimate the experimental data for total-ionization cross sections of the observed ions. No other experimental or theoretical data exist in the investigated energy range to make a direct comparison with the present results.

Bosonic atom-trimer scattering is studied in the unitary limit using momentum-space equations for four-particle transition operators. The impact of the Efimov effect on the atom-trimer scattering observables is explored, and a number of universal relations is established. Positions and widths of tetramer resonances are determined. The trimer relaxation rate constant is calculated.

We simulate the experimental possibility of observing antiferromagnetic (AF) order in bosonic mixtures of rubidium $($${}^{87}\mathrm{Rb}$$)$ and potassium $($${}^{41}\mathrm{K}$$)$ in a two-dimensional optical lattice in the presence of harmonic confinement. By tuning the interspecies interactions and the lattice heights, we have found the ground states, within the mean-field approximation, that interpolate from phase separation to AF order. For a moderate lattice height, the coexistence of the Mott and AF phases is possible for the Rb atoms whereas the K atoms remain in the AF-superfluid phase. This observation may provide an experimentally feasible route to hitherto unobserved AF order for ${}^{87}\mathrm{Rb}$-${}^{41}\mathrm{K}$ mixtures.

We report numerical and experimental investigations of spatiotemporal nonlinear optical effects leading to spectral broadening in an array of subwavelength silicon waveguides pumped with infrared femtosecond pulses. Adjusting an input pulse position across the array, we observe different patterns in the output spectra. We explain these observations using a theory of the resonant (Cherenkov) radiation emitted by temporal solitons belonging to different spatial supermodes of the array. We also demonstrate strong nonperturbative coupling of temporal dispersion and discrete diffraction in the subwavelength arrays.

We propose a theoretical scheme of quantum nondemolition measurement of two-qubit Werner state. We discuss our scheme with the two qubits restricted in a local place and then extend the scheme to the case in which two qubits are separated. We also consider the experimental realization of our scheme based on cavity quantum electrodynamics. It is very interesting that our scheme is robust against the dissipative effects introduced by the probe process. We also give a brief interpretation of our scheme finally.