We report the hyperfine coupling constants for the $6d{}^{2}D_J$ states of ${}^{133}\mathrm{Cs}$ using two-color absorption spectroscopy with sub-Doppler resolution. Two single-mode diode lasers resonantly excite cesium in a low-pressure vapor cell. The frequency scale is directly referenced to the ground hyperfine interval of ${}^{87}\mathrm{Rb}$ using a radio-frequency modulation technique. The $6d{}^{2}D_{5∕2}$ coupling constants are measured as $A=-4.66\pm 0.04\mathrm{MHz}$ and $B=0.9\pm 0.8\mathrm{MHz}$, agreeing with the literature. The $6d{}^{2}D_{3∕2}$ coupling constants are measured as $A=16.34\pm 0.03\mathrm{MHz}$ and $B=-0.1\pm 0.2\mathrm{MHz}$, which significantly improve the precision of previous measurements.

We present a detailed quantum mechanical treatment of the photodetachment of ${\mathrm{H}}^{-}$ by a short laser pulse in the presence of crossed static electric and magnetic fields. An exact analytic formula is presented for the final state electron wave function (describing an electron in both static electric and magnetic fields and a short laser pulse of arbitrary intensity). In the limit of a weak laser pulse, final state electron wave packet motion is examined and related to the closed classical electron orbits in crossed static fields predicted by Peters and Delos [Phys. Rev. A 47, 3020 (1993)]. Owing to these closed orbit trajectories, we show that the detachment probability can be modulated, depending on the time delay between two laser pulses and their relative phase, thereby providing a means to partially control the photodetachment process. In the limit of a long, weak pulse (i.e., a monochromatic radiation field) our results reduce to those of others; however, for this case we analyze the photodetachment cross section numerically over a much larger range of electron kinetic energy (i.e., up to $500{\mathrm{cm}}^{-1}$) than in previous studies and relate the detailed structures both analytically and numerically to the above-mentioned, closed classical periodic orbits.

We present a theoretical model of high-harmonic generation from diatomic molecules. The theory includes effects of alignment as well as nuclear motion and is used to predict results for ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, and ${\mathrm{D}}_2$. The results show that the alignment dependence of high-harmonics is governed by the symmetry of the highest occupied molecular orbital and that the inclusion of the nuclear motion in the theoretical description generally reduces the intensity of the harmonic radiation. We compare our model with experimental results on ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$, and obtain very good agreement.

It is known that photons produced by spontaneous parametric down-conversion can be coupled into optical fibers more efficiently by focusing the pump field. We find that focusing the pump in type-II down-conversion causes photons of ordinary and extraordinary polarization to acquire very different angular spreads, which amounts to spatial information that distinguishes between the polarization states. Numerical studies predict that the photons collected by a detector or quantum channel will be of predominantly one polarization and that the degree of polarization entanglement will be lessened in some cases.

The influence of the size and shape of a dispersing and absorbing dielectric body on the local-field-corrected spontaneous decay of an excited atom embedded in a body is studied on the basis of the real-cavity model. By means of a Born expansion of the Green tensor of the system it is shown that to linear order in the susceptibility of the body the decay rate exactly follows Tomaš’s formula found for the special case of an atom at the center of a homogeneous dielectric sphere [Phys. Rev. A 63, 053811 (2001)]. It is further shown that for an atom situated at the interior of an arbitrary dielectric body this formula remains valid beyond linear order. The case of an atom embedded in a weakly polarizable sphere is discussed in detail.

The concepts of concurrence and mode concurrence are the measures of entanglement for spin-$1∕2$ and spinless fermion systems, respectively. Based on the Jordan-Wigner transformation, any spin-$1∕2$ system is always associated with a fermion system (called the counterpart system). A comparison of concurrence and mode concurrence can be made with the aid of Marshall’s sign rule for the ground states of spin-$1∕2$ $XXZ$ and spinless fermion chain systems. We observe that there exists an inequality between concurrence and mode concurrence for the ground states of the two corresponding systems. The spin-$1∕2$ $XY$ chain system and its spinless fermion counterpart as a realistic example are discussed to demonstrate the analytical results.

The radial matrix elements connecting the ionic ${\mathrm{Ba}}^{+}6s$ ground state to low-lying excited $6p$ and $5d$ states can be extracted from the $K$ splittings of the bound $6sn\ell$ states in much the same way that ionic polarizabilities are extracted from the separations between $\ell$ states. We develop an expression for the $K$ splitting by a pair of expansions which allows us to compare the contributions of different ionic states. This comparison confirms that all but the lowest two may be safely ignored. Finally, we extract the radial ${\mathrm{Ba}}^{+}$ matrix elements $⟨6s\mid r\mid 6p⟩=4.03\left(12\right)$ and $⟨6s\mid r^2\mid 5d⟩=9.76\left(29\right)$ from the experimentally obtained $K$ splittings.

Resonance structures in the photoionization of ${\mathrm{S}}^{+}$ for the removal of a $3p$ or $3s$ electron from the ground $3s^{2}3p^3$ ${}^{4}S^o$ and excited metastable ${}^{2}D^o$ and ${}^{2}P^o$ states have been studied in the $B$-spline $R$-matrix approach. The nonorthogonal orbitals have been used for an accurate representation of the initial ${\mathrm{S}}^{+}$ bound states, the final ${\mathrm{S}}^{2+}$ ion plus photoelectron states and ${\mathrm{S}}^{2+}$ thresholds. Calculations have been carried out in 17- and 27-state close-coupling approximations. The relativistic effects have been incorporated in the Breit-Pauli Hamiltonian. Photoionization cross sections are dominated by $3s^{2}3p^2\left({}^{1}D\right)ns$ ${}^{2}D$, $3s^{2}3p^2\left({}^{1}D\right)nd$ ${}^{2}F$, ${}^{2}D$, ${}^{2}P$, and $3s3p^3({}^{5}S^o$, ${}^{3}S^o$, ${}^{3}D^o$, ${}^{3}P^o)np$ ${}^{4}P$ Rydberg series of autoionizing resonances. The resonance states are identified and analyzed to obtain resonance positions $E_r$, effective quantum numbers $n^{*}$, and widths ${\Gamma }_r$ using a procedure of eigenphase gradients. The resonance line shape and correlation parameters have also been determined. Photoionization cross sections have been calculated in both length and velocity formulations that exhibit very good agreement (within 5%) with each other for most photon energies. Our results are compared with a recent merged ion-photon beam experiment. Significant discrepancies between the theoretically predicted and experimentally measured resonance structures and continuum cross sections are noted.

The dynamics of magnetic relaxation of Tm atoms in cold helium gas is investigated using ab initio interaction potentials between $\mathrm{Tm}\left({}^{2}F\right)$ and He atoms. The interaction of $\mathrm{Tm}\left({}^{2}F\right)$ with He gives rise to four adiabatic potentials of ${\Sigma }^{+}$, $\Pi$, $\Delta$, and $\Phi$ symmetries, which are found to be degenerate to within $0.1{\mathrm{cm}}^{-1}$ at all interatomic distances larger than $R=5.4\mathrm{\AA }$. The small splitting between the interaction potentials leads to suppression of Zeeman transitions in Tm-He collisions. Our quantum scattering calculations yield a small rate constant of $1.5\times {10}^{-15}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for Zeeman relaxation of the $\mathrm{Tm}\left({}^{2}F_{7∕2}\right)$ atoms in the maximally stretched $M=7∕2$ sublevel at the temperature $0.8\mathrm{K}$, in reasonable agreement with the measured value $(5.0\pm 2.1)\times {10}^{-15}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. The sensitivity of Zeeman-relaxation cross sections to details of the interaction potentials is examined. To our knowledge, this is one of only two comparisons of ab initio quantum scattering calculations with experimental measurements of inelastic collisions at subkelvin temperatures near one Kelvin. Our work thus demonstrates the feasibility of describing cold collisions from first principles.

Differential cross sections for electron collisions with the ${\mathrm{O}}_2$ molecule in its ground $X{}^3\Sigma _g^{-}$ state, as well as excited $a{}^1\Delta _g$ and $b{}^1\Sigma _g^{+}$ states are calculated. As previously, the fixed-bond $R$-matrix method based on state-averaged complete active space self-consistent-field orbitals is employed. In addition to elastic scattering of electron with the ${\mathrm{O}}_2$ $X{}^3\Sigma _g^{-}$, $a{}^1\Delta _g$, and $b{}^1\Sigma _g^{+}$ states, electron impact excitation from the $X{}^3\Sigma _g^{-}$ state to the $a{}^1\Delta _g$ and $b{}^1\Sigma _g^{+}$ states as well as $6\mathrm{eV}$ states of $c{}^1\Sigma _u^{-}$, $A^{\prime }{}^3\Delta _u$, and $A{}^3\Sigma _g^{+}$ states is studied. Differential cross sections for excitation to the $6\mathrm{eV}$ states have not been calculated previously. Electron impact excitation to the $b{}^1\Sigma _g^{+}$ state from the metastable $a{}^1\Delta _g$ state is also studied. For electron impact excitation from the ${\mathrm{O}}_2$ $X{}^3\Sigma _g^{-}$ state to the $b{}^1\Sigma _g^{+}$ state, our results agree better with the experimental measurements than previous theoretical calculations. Our cross sections show angular behavior similar to the experimental ones for transitions from the $X{}^3\Sigma _g^{-}$ state to the $6\mathrm{eV}$ states, although the calculated cross sections are up to a factor of 2 larger at large scattering angles. For the excitation from the $a{}^1\Delta _g$ state to the $b{}^1\Sigma _g^{+}$ state, our results marginally agree with the experimental data except for the forward scattering direction.

Detailed analyses of previous measurements, combined with additional measurements reported here, have been made of electron interference structures observed in $60\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{Kr}}^{34+}+{\mathrm{H}}_2$ collisions. Results are used to characterize the angular dependence of the primary interference structures over a wide range of electron ejection angles, particularly backward angles, and, additionally, to search for high-frequency structures as reported recently for $1–5\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{H}}^{+}+{\mathrm{H}}_2$ collisions [Hossain et al., Phys. Rev. A 72, 010701(R) (2005)]. The data for backward ejection angles, in combination with earlier data, permit a detailed comparison with theory over the range 30°–150°, showing that none of the existing theories predict accurately the observed oscillation frequencies for backward angles. Electron spectra for 90° and 150° taken in small energy steps and with improved statistics compared to earlier measurements were examined by means of a Fourier analysis but no evidence of the high-frequency structures reported for ${\mathrm{H}}^{+}+{\mathrm{H}}_2$ collisions was found.

A large sample $(N\approx {10}^4)$ of fullerene ions $(m=720\mathrm{a}.\mathrm{u})$ is cooled by means of a much smaller number$(\approx 100)$ of laser-cooled magnesium ions $(m=24\mathrm{a}.\mathrm{u})$. The results demonstrate that sympathetic cooling of large molecules to low temperatures is feasible. The temperature of the ${}^{24}\mathrm{Mg}^{+}$ ions in the mixed ${\mathrm{Mg}}^{+}\text{−}{{\mathrm{C}}_{60}}^{+}$ ion cloud stored in an rf trap is found to be $T_{\mathrm{Mg}}=5\mathrm{K}$ from their fluorescence signal. Molecular dynamics simulations are used to obtain the corresponding equilibrium temperature of the fullerene ions, and show that $T_{{\mathrm{C}}_{60}}=14\mathrm{K}$.

We present a straightforward scheme for creating macroscopic superpositions of different superfluid flow states of Bose-Einstein condensates trapped in optical lattices. This scheme has the great advantage that all the techniques required are within the reach of current experiments. Furthermore, the relative difficulty of creating superpositions scales favorably with the size of the state. This means that this scheme may be well suited to creating superpositions involving large numbers of particles. Such states may have interesting technological applications such as making quantum-limited measurements of angular momentum.

A Bose-Einstein condensate in three-dimensional free space is known to be unstable against expansion or collapse if the scattering length of atoms is constant. We propose a method to produce a stable self-trapped condensate in which nondestructive measurement of the condensate’s peak density is used to perform feedback control of the scattering length. The stability is shown to be robust against experimental imperfections in the measurements.

We consider two dynamically deforming plates immersed in the vacuum of a scalar field. We study both the (generalized) Neumann and the Dirichlet boundary conditions on the surfaces. For rough plates undergoing small displacements parallel or perpendicular to the normal axis, the mass correction, the vacuum viscosity, and the dissipation rate arising from photon emission inside the cavity, are calculated. In the case of motion along the normal axis, these quantities have no dependence on the shape of plates, and the Neumann ones are greater. We examine the specific example of two corrugated surfaces of a wave number $k_{1p}$ and mean separation $H$, performing lateral oscillation with a frequency ${\omega }_{1p}$. In contrast to Dirichlet photons, Neumann photons can be excited for all values of $k_{1p}$, $H$, and ${\omega }_{1p}$. For short cavity lengths, the number of Neumann photons increases as $H^{-2}$. The phase difference between the harmonic motion of plates can be used to tune the dissipation rate. Neumann mass correction and dissipation rate are greater than Dirichlet ones. We calculated the force exerted on two corrugated plates that are moving uniformly in the lateral directions. This lateral force decreases as $\exp (-k_{1p}H)$ if $k_{1p}H>1$, increases as $H^{-5}$ if $k_{1p}H<0.1$, and is stronger in the case of the Dirichlet boundary condition.

The Casimir force is the ultimate background in ongoing searches for extragravitational forces in the micrometer range. Eccentric cylinders offer favorable experimental conditions for such measurements as spurious gravitational and electrostatic effects can be minimized. Here we report on the evaluation of the exact Casimir interaction between perfectly conducting eccentric cylinders using a mode summation technique, and study different limiting cases of relevance for Casimir force measurements, with potential implications for the understanding of mechanical properties of nanotubes.

The dynamics of a spin-$1∕2$ particle coupled to a nuclear spin bath through an isotropic Heisenberg interaction is studied as a model for the spin decoherence in quantum dots. The time-dependent polarization of the central spin is calculated as a function of the bath-spin distribution and the polarizations of the initial bath state. For short times, the polarization of the central spin shows a Gaussian decay, and at later times it is revived displaying nonmonotonic time dependence. The decoherence time scale depends on moments of the bath-spin distribuition, and also on the polarization strengths in various bath-spin channels. The bath polarizations have a tendency to increase the decoherence time scale. The effective dynamics of the central spin polarization is shown to be described by a master equation with non-Markovian features.

Laser-assisted antihydrogen $\left(\overline{\mathrm{H}}\right)$ formation cross sections (differential and total) for collisions of antiprotons with positronium (Ps) are studied in the framework of the eikonal approximation for two geometries, when the field polarization is parallel $\left({\Vert }^L\right)$ or perpendicular $\left({\perp }^r\right)$ to the incident Ps momentum. The variations of the $\overline{\mathrm{H}}$ formation cross sections with respect to the field strength and the laser photon energy are studied for the multiphoton (absorption and emission) processes. The contribution of the atomic (both Ps and $\overline{\mathrm{H}}$) dressing terms to the enhancement of the $\overline{\mathrm{H}}$ formation cross section is studied for both the geometries (${\Vert }^L$ and ${\perp }^r$). The most important prediction from the present work is the enhancement of the field-free (FF) $\overline{\mathrm{H}}$ formation cross sections particularly at lower incident energies when the system $(\mathrm{Ps}+\overline{p})$ is irradiated by a single mode, linearly polarized laser, the enhancement being more pronounced for a wider range of incident energy in the ${\perp }^r$ geometry than in the ${\Vert }^L$ one.

We have measured single- and multiple-target ionization cross sections for the ${\mathrm{F}}^{-}+\mathrm{Ar}$ collision system. Measurements of the final target and projectile charge states were performed in coincidence, separating the collision channels for single-, double-, and triple-projectile-electron loss and for direct ionization. The studied velocity region extends from $v=0.46$ to $v=1.45$ atomic units. Results are compared with existing ${\mathrm{H}}^{-}+\mathrm{Ar}$ data as well as with Ar multiple ionization by protons, electrons, and antiprotons. For the direct-ionization channel, ratios for multiple-to-single target ionization are similar to those found for ${\mathrm{H}}^{+}+\mathrm{Ar}$ collisions. For this channel multiple ionization is well described by independent single-ionization events by a frozen projectile. For the projectile-electron-loss collision channels, on the other hand, the correlation between projectile electrons and target electrons plays an important role. Our data show that the average final charge state of the target, $⟨q⟩$, increases steeply with the final charge state of the projectile, while an independent-particle model (neglecting two-center electron-electron correlation) only accounts for small variations of $⟨q⟩$.

In this work, we present a theoretical study on elastic electron collisions with the four ${\mathrm{C}}_2{\mathrm{N}}_2$ isomers. More specifically, calculated differential, integral, and momentum transfer cross sections are reported in the $1–100\mathrm{eV}$ energy range. Calculations are performed at both the static-exchange-absorption and the static-exchange-polarization-absorption levels. The iterative Schwinger variational method combined with the distorted wave approximation is used to solve the scattering equations. Our study reveals an interesting trend of the calculated cross sections for the four isomers. In particular, strong isomer effect is seen at low incident energies. Also, we have identified a shape resonance which leads to a depression in the calculated partial integral cross section.