We present ab initio calculations of the $W_A$ parameter of the $P$-odd spin-rotational Hamiltonian for a variety of diatomic molecules, including the group 2 and group 12 halides. The results were obtained by relativistic Dirac-Hartree-Fock and density functional theory approaches and corrected for core polarization effects. Strong enhancement of $W_A$ is found for the group 12 diatomic halides, which should be helpful in future determination of the nuclear anapole moment.

Many recent applications of time-dependent density functional theory begin in an initially excited state and propagate it using an adiabatic approximation for the exchange-correlation potential. This, however, inserts the excited-state density into a ground-state approximation. By studying a series of model calculations, we highlight the relevance of initial-state dependence of the exact functional when starting in an excited state, discuss different valid choices of the initial Kohn-Sham state, and explore the errors inherent in the adiabatic approximation that neglects this dependence.

It is shown that the atom-molecule collision problem in the presence of an external electric field can be solved using the total angular momentum representation in the body-fixed coordinate frame, leading to a computationally efficient method for ab initio modeling of low-temperature scattering phenomena. Our calculations demonstrate rapid convergence of the cross sections for vibrational and Stark relaxation in He-CaD collisions with the number of total angular momentum states in the basis set, leading to a 5- to 100-fold increase in computational efficiency over the previously used methods based on the fully uncoupled space-fixed representation. These results open up the possibility of carrying out numerically converged quantum scattering calculations on a wide array of atom-molecule collisions and chemical reactions in the presence of electric fields.

We report on total cross section measurements for positron scattering from the chiral enantiomers ($+$)-methyl ($R$)-2-chloropropionate and (–)-methyl ($S$)-2-chloropropionate. The energy range of the present study was 0.1–50 eV, while the energy resolution of our incident positron beam was ∼0.25 eV (FWHM). As positrons emanating from β decay in radioactive nuclei have a high degree of spin polarization, which persists after moderation, we were particularly interested in probing whether the positron helicity differentiates between the measured total cross sections of the two enantiomers. No major differences were, however, observed. Finally, quantum chemical calculations, using the density functional theory based B3LYP-DGTZVP model within the gaussian 09 package, were performed as a part of this work in order to assist us in interpreting some aspects of our data.

We present a theory for excitation of heavy hydrogenlike projectile ions by light target atoms in collisions where the momentum transfers to the atom are very large on the atomic scale. It is shown that in this process the electrons and the nucleus of the atom behave as (quasi-) free particles with respect to each other and that their motion is governed by the field of the nucleus of the ion. The effect of this field on the atomic particles can be crucial for the contribution to the excitation of the ion caused by the electrons of the atom but, because of large nuclear mass, may be neglected in the contribution to the excitation due to the nucleus of the atom. The theory is applied to calculate excitation of Bi${}^{82+}$(1$s$) ions in collisions with hydrogen.

In a recent publication [Schütte et al., Phys. Rev. Lett. (to be published)] it was demonstrated, both experimentally and theoretically, that Auger electrons are subject to an energetic chirp if a three-body-interaction dubbed postcollision interaction (PCI) is involved. Here, we extend previous theoretical work and give a detailed analysis of field-assisted PCI based on numerical solutions of the time-dependent Schrödinger equation, extensive Monte Carlo–averaged molecular dynamics simulations, and analytical theory. The dependence on various streaking and excitation conditions is investigated, and we discuss how these findings may help to improve XUV pulse characterization as well as understanding of ultrafast atomic processes.

We explore the laser-induced ionization dynamics of N${}_2$ and CO${}_2$ molecules subjected to a few-cycle, linearly polarized, 800 nm laser pulse using effective two-dimensional single-active-electron time-dependent quantum simulations. We show that the electron recollision process taking place after an initial tunnel ionization stage results in quantum interference patterns in the energy-resolved photoelectron signals. If the molecule is initially aligned perpendicular to the field polarization, the position and relative heights of the associated fringes can be related to the molecular geometrical and orbital structure by using a simple inversion algorithm which takes into account the symmetry of the initial molecular orbital from which the ionized electron is produced. We show that it is possible to extract interatomic distances in the molecule from an averaged photon-electron signal with an accuracy of a few percent.

We describe theoretically a setup in which a tapered optical nanofiber is introduced into an optical lattice potential for cold atoms. First, we consider the disturbance to the geometry of the lattice potential due to scattering of the lattice lasers from the dielectric fiber surface and show that the resulting distortion to the lattice can be minimized by placing the fiber at an appropriate position in the lattice. We then calculate the modifications of the local potentials that are achievable by transmitting off-resonant light through the fiber. The availability of such a technique holds the potential to deterministically create and address small well-defined samples of atoms in the evanescent field of the tapered nanofiber.

Photoionization of aligned and fixed nuclei three-dimensional H${}_2{}^{+}$ and two-dimensional H${}_2$ by intense circularly polarized attosecond extreme ultraviolet laser pulses is investigated from numerical solutions of the time-dependent Schrödinger equation. Molecular above-threshold-ionization angular distributions are found to be rotated with respect to the two laser perpendicular polarizations or, equivalently the symmetry axes of the molecule. The angle of rotation is critically sensitive to laser wavelength $\lambda$, photoelectron energy $E_{\text{en}}$, and molecular internuclear distance $R$. The correlated interaction of the two electrons in H${}_2$ is shown to also influence such angular distribution rotations in different electronic states.

We propose a dark-state cooling scheme of trapped ion systems using standing waves in the Lamb-Dicke limit. By exploiting the property of standing waves, the heating effects caused by the carrier and the blue sideband transitions vanish and lower final phonon number can be achieved. Different from other dark-state cooling schemes, our scheme is more robust under the fluctuations of laser intensities.

We investigate single-particle properties of a one-component Fermi gas with a tunable $p$-wave interaction. Including pairing fluctuations associated with this anisotropic interaction within a $T$-matrix theory, we calculate the single-particle density of states, as well as the spectral weight, above the superfluid transition temperature $T_{\mathrm{c}}$. Starting from the weak-coupling regime, we show that the so-called pseudogap first develops in these quantities with increasing the interaction strength. However, when the interaction becomes strong to some extent, the pseudogap becomes obscure to eventually disappear in the intermediate coupling regime. In the strong-coupling regime, the excitation gap associated with the formation of tightly bound molecules again opens. This nonmonotonic interaction dependence of the excitation gap is quite different from the case of an $s$-wave interaction, where the pseudogap simply develops with increasing the interaction strength, which continuously changes into the molecular excitation gap. The difference between the two cases is shown to originate from the momentum dependence of the $p$-wave interaction, which vanishes in the low momentum limit. We also identify the pseudogap regime in the phase diagram with respect to the temperature and the $p$-wave interaction strength. Since the pseudogap is a precursor phenomenon of the superfluid phase transition, our results would be useful for the research toward the realization of $p$-wave superfluid Fermi gases.

The properties of Bose-Einstein-condensed systems of hard spheres at high density are studied by taking into account higher-order corrections beyond the Hartree-Fock-Bogoliubov approximation. Based on a diagrammatic technique of the perturbation expansion starting from the Bogoliubov approximation, we show that the effective interactions separate into two distinct parts: the screened and condensate-mediated interactions. The latter is described by the exchange of virtual quasiparticles between noncondensate bosons via the Bose-Einstein condensate and is attractive for small energy transfer. We calculate the condensation temperature, excitation spectrum, and condensate density in the whole region of the gas parameter. It is shown that the condensate temperature decreases compared to that of an ideal Bose gas due to hard-sphere interactions. We find that the condensate-mediated attraction between noncondensate bosons leads to an enhancement of the anomalous self-energy and, as a consequence, to the emergence of a roton minimum in the excitation spectrum and to the strong suppression of the condensate fraction in the region of high density.

We present a density-functional theory for the one-dimensional harmonically trapped Bose-Fermi mixture with repulsive contact interactions. The ground-state density distribution of each component is obtained by solving the Kohn-Sham equations numerically based on the local density approximation and the exact solution for the homogeneous system given by Bethe ansatz method. It is shown that for sufficiently strong interaction, a considerable amount of fermions are repelled out of the central region of the trap, exhibiting partial phase separation of Bose and Fermi components. Oscillations emerge in the Bose density curves, reflecting the strong correlation with fermions. For infinitely strong interaction, the ground-state energy of the mixture and the total density are consistent with the scenario that all atoms in the mixture are fully fermionized.

We study properties of a trapped dipolar Bose-Einstein condensate (BEC) in a circular ring or a spherical shell using the mean-field Gross-Pitaevskii equation. In the case of the ring-shaped trap we consider different orientations of the ring with respect to the polarization direction of the dipoles. In the presence of long-range anisotropic dipolar and short-range contact interactions, the anisotropic density distribution of the dipolar BEC in both traps is discussed in detail. The stability condition of the dipolar BEC in both traps is illustrated in a phase plot of dipolar and contact interactions. We also study and discuss the properties of a vortex dipolar BEC in these traps.

We propose and demonstrate an effective mode-filtering technique of non-Gaussian states generated by photon subtraction. More robust non-Gaussian states have been obtained by removing noisy low frequencies from the original mode spectrum. We show that non-Gaussian states preserve their nonclassicality after quantum teleportation to a higher degree when they have been mode filtered. This is indicated by a stronger negativity, $-0.033\pm 0.005$, of the Wigner function at the origin, compared to $-0.018\pm 0.007$ for states that have not been mode filtered. This technique can be straightforwardly applied to various kinds of photon-subtraction protocols and can be a key ingredient in a variety of applications of non-Gaussian states, especially teleportation-based protocols toward universal quantum information processing.

Motivated by recent “circuit QED” experiments we investigate the noise properties of coherently driven nonlinear resonators. By using Josephson junctions in superconducting circuits, strong nonlinearities can be engineered, which lead to the appearance of pronounced effects already for a low number of photons in the resonator. Based on a master equation approach we determine the emission spectrum and observe for typical circuit QED parameters, in addition to the primary Raman-type peaks, second-order peaks. These peaks describe higher harmonics in the slow noise-induced fluctuations of the oscillation amplitude of the resonator and provide a clear signature of the nonlinear nature of the system.

We consider the propagation of ultrashort solitons in noncentrosymmetric quadratically nonlinear optical media described by a general Hamiltonian of multilevel atoms. We use a long-wave approximation to derive a coupled system of Korteweg–de Vries equations describing ultrashort soliton evolution in such materials. This model was derived by using a rigorous application of the reductive perturbation formalism (multiscale analysis). The study of linear eigenpolarizations in the degenerate case and the corresponding formation of half-cycle solitons from few-cycle-pulse inputs are also presented.

We put forward a general classical approach to obtain the quantum dipole-dipole interaction (DDI) between two two-level “atoms” in arbitrary nanostructures, in which the transfer rate of the DDI is analytically expressed as the difference between the two classical dipoles’ total radiation power and the sum of the two individual dipole's radiation powers. The radiation power can be calculated by the finite-difference time-domain method. We apply the theory to investigate the DDI in a photonic crystal nanocavity. It is found that strong DDI at a distance can be achieved under resonant conditions and with a high quality factor, and the attractive or repulsive properties of the DDI can be manipulated. Our results should be significant for solid-state quantum-information processing based on the DDI.

Electromagnetic sources, e.g., lasers, antennas, diffusers, or thermal sources, produce a wave field that interacts with objects to transfer to them its momentum. We show that the photonic force exerted on a dipolar particle in the near field of a planar statistically homogeneous fluctuating source uniquely depends on and acts along the coordinate perpendicular to its surface. The gradient part of this force is contributed by only the evanescent components of the emitted field, its sign being opposite that of the real part of the particle polarizability. The nonconservative force is due to the propagating components, which are repulsive and constant. In addition, the source coherence length adds a degree of freedom since it largely affects these forces. The excitation of plasmons in the source surface drastically enhances the gradient force while slightly weakening the nonconservative scattering plus curl force. Hence these consequences obtained for random and partially coherent wave fields emitted by the sources addressed here should be relevant for particle manipulation at the subwavelength scale.

Nondegenerate four-wave mixing driven by two pulsed pumps transfers the quantum state of an input signal pulse to an output idler pulse, which is a frequency-converted and reshaped version of the signal. By varying the pump shapes appropriately, one can connect signal and idler pulses with arbitrary durations and shapes. This process enables a variety of functions required by quantum information networks.