As an important step toward an atomic parity violation experiment in one single trapped Ra${}^{+}$ ion, laser spectroscopy on short-lived ${}^{212,213,214}\mathrm{Ra}$${}^{+}$ ions was conducted. The isotope shift of the $6\hspace{0.5em}{}^2{D}_{3/2}$-$7\hspace{0.5em}{}^2{P}_{1/2}\hspace{0.5em}$and $6\hspace{0.5em}{}^2{D}_{3/2}$-$7\hspace{0.5em}{}^2{P}_{3/2}\hspace{0.5em}$transitions and the hyperfine structure constants of the $7\hspace{0.5em}{}^2{P}_{1/2}\hspace{0.5em}$and $6\hspace{0.5em}{}^2{D}_{3/2}\hspace{0.5em}$states in ${}^{213}\mathrm{Ra}$${}^{+}$ were measured, which provides a benchmark for the required atomic theory. A lower limit of $232(4)$ ms for $6\hspace{0.5em}{}^2{D}_{5/2}\hspace{0.5em}$state lifetime was determined.

Cold fermionic atoms with three different hyperfine states with SU($3$) symmetry confined in one-dimensional optical lattices show color-charge separation, generalizing the conventional spin-charge separation for interacting SU($2$) fermions in one dimension. Through time-dependent density-matrix renormalization-group simulations, we explore the features of this phenomenon for a generalized SU($3$) Hubbard Hamiltonian. In our numerical simulations of finite-size systems, we observe different velocities of the charge and color degrees of freedom when a Gaussian wave packet or a charge (color) density response to a local perturbation is evolved. The differences between attractive and repulsive interactions are explored and we note that neither a small anisotropy of the interaction, breaking the SU($3$) symmetry, nor the filling impedes the basic observation of these effects.

We describe a quantum key distribution protocol based on pairs of entangled qubits that generates a secure key between two partners in an environment of unknown and slowly varying reference frame. A direction of particle delivery is required, but the phases between the computational basis states need not be known or fixed. The protocol can simplify the operation of existing setups and has immediate applications to emerging scenarios such as earth-to-satellite links and the use of integrated photonic waveguides. We compute the asymptotic secret key rate for a two-qubit source, which coincides with the rate of the six-state protocol for white noise. We give the generalization of the protocol to higher-dimensional systems and detail a scheme for physical implementation in the three-dimensional qutrit case.

We consider a guided Bose-Einstein matter wave flowing through a disordered potential. We determine the critical velocity at which superfluidity is broken and compute its statistical properties. They are shown to be connected to extreme values of the random potential. Experimental implementations of this physics are discussed.

We investigate the practicality of the method proposed by Maciel et al. [Phys. Rev. A. 80, 032325 (2009).] for detecting the entanglement of two spatial qutrits (three-dimensional quantum systems), which are encoded in the discrete transverse momentum of single photons transmitted through a multislit aperture. The method is based on the acquisition of partial information of the quantum state through projective measurements, and a data processing analysis done with semidefinite programs. This analysis relies on generating gradually an optimal entanglement witness operator, and numerical investigations have shown that it allows for the entanglement detection of unknown states with a cost much lower than full state tomography.

We analyze the role of dimensionality in the time evolution of discrete-time quantum walks through the example of the three-state walk on a two-dimensional triangular lattice. We show that the three-state Grover walk does not lead to trapping (localization) or recurrence to the origin, in sharp contrast to the Grover walk on the two-dimensional square lattice. We determine the power-law scaling of the probability at the origin with the method of stationary phase. We prove that only a special subclass of coin operators can lead to recurrence, and there are no coins that lead to localization. The propagation for the recurrent subclass of coins is quasi-one dimensional.

The static electric dipole polarizabilities for a variety of atoms and molecules are calculated using a finite-field method based on ab initio pseudopotential density functional theory. The calculations are performed in real space without an explicit basis. We employ different representations of the exchange-correlation potential: the local density approximation, generalized gradient approximation, and asymptotically corrected functionals introduced by van Leeuwen and Baerends and by Casida and Salahub. Our calculations show that the computed values of polarizabilities are strongly influenced by the asymptotic behavior of the density functional exchange-correlation potential. The accuracy of theoretical atomic and molecular polarizabilities is substantially improved by the use of asymptotically correct exchange-correlation functionals. This result can be explained in terms of electronic excitation energies and the polarizability sum rule.

We report on the experimental observation of high-resolution rotationally resolved spectra of vibrational polyads $10$ and $12$ of methane lying approximately halfway to the dissociation energy. The spectra were obtained at 295 K and 124 K and pressures as low as 200 mbar using a highly sensitive laser-induced grating (LIG) technique. The spectra correspond to direct single-photon absorption transitions from the ground state with cross sections as low as ${10}^{-25}$ to ${10}^{-26}$ cm${}^2$ molecule${}^{-1}$. We discuss theoretical developments toward the complete analysis of these transitions.

We present a joint experimental and theoretical investigation to resolve the discrepancy in the ratio of relative peak cross sections for narrow atomic resonances among various experimental spectra and also between theory and experiment. Our study includes an effort to measure both the absorption and ionization spectra in a single experimental setup. We also present a careful analysis of the effect on the resonance structure due to the Doppler broadening at finite temperature when the Doppler width is greater than the natural linewidth of the resonance. In addition, we demonstrate that the column density strongly affects not only the absorption structure profile of a narrow atomic resonance but also the ionization spectra measured in an ionization chamber. From the good agreement reported in this article between the observed and the theoretically simulated spectra for the pressure-dependent peak cross sections and the effective asymmetry parameter for the lowest resonance of the He $(1,0){}_2^{-}$ series, we are able to characterize the monochromator (i.e., slit) function of a given light source, including its estimated energy resolution.

On the basis of the Floquet formalism, the ionization mechanisms of atomic hydrogen in circularly and linearly polarized intense laser fields are discussed. By using the complex scaling method in the velocity gauge, the pole positions of the scattering-matrix on the complex quasienergy Riemann surface are calculated, and pole trajectories with respect to the variation of the laser intensity are obtained. In the low-frequency regime, the pole trajectory exhibits a smooth ponderomotive energy shift in the case of circular polarization. In contrast, the smoothness is lost in the case of linear polarization. In the high-frequency regime, the pole trajectories exhibit the stabilization phenomenon for both the types of polarization. These observations are elucidated by a unified picture based on the analysis of the adiabatic potentials for the radial motion of the electron in the acceleration gauge. The ionization in the case of circular polarization of the low-frequency regime is governed by the electron tunneling through a barrier of a single adiabatic potential. The stabilization in the high-frequency regime can be explained by the change in the avoided crossings among the adiabatic potential curves. The transition between the different frequency regimes is explicable by the change in the structure of the adiabatic potentials. The difference caused by the type of polarization is ascribable to the difference in the space-time symmetry.

We present an analytical inversion technique, which can be used to recover ionization probabilities from spatially averaged data in an $N$-dimensional detection scheme. The solution is given as a power series in intensity. For this reason, we call this technique a multiphoton expansion (MPE). The MPE formalism was verified with an exactly solvable inversion problem in two dimensions, and probabilities in the postsaturation region, where the intensity-selective scanning approach breaks down, were recovered. In three dimensions, ionization probabilities of $\mathrm{Xe}$ were successfully recovered with MPE from simulated (using the Ammosov-Delone-Krainov tunneling theory) ion yields. Finally, we tested our approach with intensity-resolved benzene-ion yields, which show a resonant multiphoton ionization process. By applying MPE to this data (which were artificially averaged), the resonant structure was recovered, which suggests that the resonance in benzene may have been observed in spatially averaged data taken elsewhere.

We present a general mapping between continuous and lattice models of Bose and Fermi gases in one dimension, interacting via local two-body interactions. For $s$-wave interacting bosons we arrive at the Bose-Hubbard model in the weakly interacting, low-density regime. The dual problem of $p$-wave interacting fermions is mapped to the spin-$1/2$ $\mathit{XXZ}$ model close to the critical point in the highly polarized regime. The mappings are shown to be optimal in the sense that they produce the least error possible for a given discretization length. As an application we examine the ground state of an interacting Fermi gas in a harmonic trap, calculating numerically real-space and momentum-space distributions as well as two-particle correlations. In the analytically known limits the convergence of the results of the lattice model with the continuous one is shown.

We show how Fermi-liquid theory can be applied to ultracold Fermi gases, thereby expanding their “simulation” capabilities to a class of problems of interest to multiple physics subdisciplines. We introduce procedures for measuring and calculating position-dependent Landau parameters. This lays the groundwork for addressing important controversial issues: (i) the suggestion that thermodynamically, the normal state of a unitary gas is indistinguishable from a Fermi liquid and (ii) that a fermionic system with strong repulsive contact interactions is associated with either ferromagnetism or localization; this relates as well to ${}^3\mathrm{He}$ and its $p$-wave superfluidity.

We demonstrated a $7.36$ nm Ni-like samarium soft-x-ray laser, pumped by $36$ J of a neodymium:glass chirped-pulse amplification laser. Double-pulse single-beam non-normal-incidence pumping was applied for efficient soft-x-ray laser generation. In this case, the applied technique included a single-optic focusing geometry for large beam diameters, a single-pass grating compressor, traveling-wave tuning capability, and an optimized high-energy laser double pulse. This scheme has the potential for even shorter-wavelength soft-x-ray laser pumping.

A monochromatic laser pumping a parametric down-conversion crystal generates frequency-entangled photon pairs. We study this experimentally by addressing such frequency-entangled photons at telecommunication wavelengths (around $1550$ nm) with fiber-optics components such as electro-optic phase modulators and narrow-band frequency filters. The theory underlying our approach uses the notion of frequency-bin entanglement. Our results show that the phase modulators address coherently up to eleven frequency bins, leading to an interference pattern which can violate by more than five standard deviations a Bell inequality adapted to our setup.

We observe the complete dynamics of the propagation of very intense, femtosecond laser pulses in air under tight focusing conditions via direct imaging of the entire interaction zone. The whole life history of the focused pulses is then reconstructed by means of numerical simulations. We show that beam breakup leads to a dual-rate increase in filament numbers with laser power. Linearly and circularly polarized pulses give rise to beam breakup and fusion governed by external focusing conditions. For tight focusing conditions, intensity saturation due to plasma generation and nonlinear losses does not limit the intensity growth, thereby giving access to a new propagation regime featured by an efficient laser energy deposition in fully ionized air and intense ${10}^{15}$ W/cm${}^2$ pulses at the focus.

This brief report is a follow-up to the recent proposal to use La${}^{-}$ as another candidate, in addition to Os${}^{-}$, in laser cooling of anions, which can then be used to cool antiprotons sympathetically. Using the relativistic configuration interaction formalism, we calculate the photodetachment cross sections of the upper laser cooling state La${}^{-}$ $5d$$6s^2$$6p\hspace{0.5em}{}^3{D}_1$ and Os${}^{-}$ $5d^6$$6s^2$$6p\hspace{0.5em}{}^6{D}_{9/2}$. Our results show that La${}^{-}$ has a very similar two-photon detachment loss as Os${}^{-}$, retaining it as another promising candidate for cooling antiprotons sympathetically.

We present analytical solutions for the problem of a two-level atom driven by a class of chirped pulses. The solutions are given in terms of Heun functions. By use of the appropriate chirping parameters, an enhancement of four orders of magnitude in the population transfer is obtained.

Photoelectron angular distributions (PADs) recorded for the ${\mathrm{O}}_2$($X$ ${}^3{\Sigma }_g^{-}$) $\leftarrow$ ${\mathrm{O}}_2^{-}$($X$ ${}^2$${\Pi }_g$) band show significant vibrational dependence. Experimental evidence of vibrational influence on the PAD has, to date, been sparse. Consequently, little attention has been paid to vibrational effects in the consideration of direct detachment processes by recent theoretical treatments. The results presented here demonstrate the sensitivity of the PAD to vibronic coupling in the anion ground electronic state, a phenomenon which is usually neglected in direct molecular anion photodetachment. These results provide the essential data for the evaluation and refinement of existing theoretical models.