We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited-state lifetime and radiative coupling strength between the two atoms. We demonstrate that steady-state SGE can be established by incoherently pumping the atoms to their excited states. We have shown that an appropriate rate of incoherent pump can help in producing optimal steady-state SGE. The multilevel systems offer us more channels to establish entanglement. The system under consideration can be realized in a tight trap or atoms/ions doped in a solid substrate.

We investigate how quantum coincidence interferometry is affected by a controllable manipulation of transverse wave vectors in type-II parametric down-conversion using adaptive optics techniques. In particular, we discuss the possibility of spatial walk-off compensation in quantum interferometry and an effect of even-order spatial aberration cancellation.

We present a model applicable to cold diatomic collisions and solve the close-coupled equations for the particular ${{}^6\text{L}\text{i}}_2$ system. Feshbach resonances are determined ab initio for both $s$ and $p$ waves. The $s$-wave scattering lengths are reported for all possible hyperfine states as a function of magnetic field strengths between 0 and 1500 G. In addition, $p$-wave scattering lengths are calculated for selected hyperfine states. Matrix elements for the hyperfine, Zeeman, and rotational Hamiltonian were worked out by the use of the molecular Hund’s case (a) basis set. All relevant matrix elements are reported. The short-range hyperfine interaction has been included in the calculations, and its effect on the scattering length are investigated. Hyperfine parameters were obtained from separate ab initio calculations.

Long-lived metastable states of ${\text{Yb}}^{+}$ ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of ${\text{Yb}}^{+}$ ions into the long-lived ${{}^{2}F}_{7/2}$ state by means of collisions between He buffer gas and ${\text{Yb}}^{+}$ ions held in a linear Paul trap. Transfer rates were measured as functions of buffer-gas pressure and repump-laser power, and the collisional population transfer rates were extracted. The measured transfer rate coefficients are $8.32\left(75\right)\times {10}^{-11}$ and $8.65\left(33\right)\times {10}^{-11}{\text{cm}}^3/\text{s}$ for the collisional processes ${{}^{2}P}_{1/2}\to {{}^{2}D}_{5/2}$ and ${{}^{2}D}_{3/2}\to {{}^{2}F}_{7/2}$, respectively.

Antiferromagnetic, Mott-insulator, $d$-wave, and gossamer superfluid phases are calculated for two-dimensional (2D) square lattices from the extended Hubbard $\left(t\text{−}J\text{−}U\right)$ model using the Gutzwiller projection method and renormalized mean-field theory. The phase separation between antiferromagnetic and $d$-wave superfluid phases is found near half filling when the on-site repulsion exceeds $U\gtrsim 7.3t$ and coincides with a first-order transition in the double occupancy. The phase separation is thus predicted for 2D optical lattices with ultracold Fermi atoms whereas it is inhibited in cuprates by Coulomb frustration which instead may lead to stripes. In a confined optical lattice the resulting density distribution is discontinuous and with extended Mott plateau which enhances the antiferromagnetic phase but suppresses the superfluid phase. Observation of Mott-insulator, antiferromagnetic, stripe, and superfluid phases in density and momentum distributions and correlations is discussed.

We investigate the dynamics of a Bose-Einstein condensate held in an optical lattice under the influence of a strong periodic driving potential. Studying the mean-field version of the Bose-Hubbard model reveals that the condensate becomes dynamically unstable when the effective intersite tunneling becomes negative. We further show how controlling the sign of the tunneling can be used to manage the dispersion of an atomic wave packet.

A technique is described by which light-induced gauge potentials allow systems of ultracold neutral atoms to behave like charged particles in a magnetic field. Here, atoms move in a uniform laser field with a spatially varying Zeeman shift and experience an effective magnetic field. This technique is applicable for atoms with two or more internal ground states. Finally, an explicit model of the system using a single-mode two-dimensional Gross-Pitaevskii equation yields the expected vortex lattice.

We consider an electron interacting with a Bose-Einstein condensate of atoms that can form negative ions. The binding energy $E_a$ of an electron by a single neutral atom gives rise to a continuous band of electronic quantum states resulting from the process of charge exchange among the condensate atoms. When such a condensate is placed in between the two leads done from a material with Fermi energy close to $E_a$, the lead electrons can tunnel through the condensate via this band thus resulting in the condensate electroconductance. It turns out that this process is very sensitive to the interatomic distance, and it gets strongly suppressed by the quantum fluctuations of the condensate density with respect to the prediction of the mean-field theory as the result. We adapt the standard field theory methods originally developed for description of a particle propagating through a disordered potential and present an exactly soluble analytical model of the process. In contrast with the standard description widely known in the theory of disordered systems, we take into account inelastic processes associated with quantum transitions in the condensate. Possibilities of the experimental observation of the phenomenon are discussed.

We investigate the time dynamics of light-induced desorption of Rb atoms in hollow-core photonic-band-gap fibers and demonstrate all-optical generation of precisely controlled Rb-vapor densities. We also compare the performance of the desorption process in an unmodified fiber with one with an organosilane-coated core, and based on the vapor depletion and recovery behavior, we propose a mechanism to describe the desorption processes. We further demonstrate that high densities of Rb vapor can be generated after the desorption beam is switched off and use it to realize $\Lambda$-scheme electromagnetically induced transparency at control powers as low as 80 nW.

We study the entanglement distillability of bipartite mixed states of two modes of a free Dirac field as seen by two relatively accelerated parties. It is shown that there are states that will change from distillable into separable for a certain value of acceleration. We exemplify these criteria in the context of Werner states.

We consider multiple teleportation in the Knill-Laflamme-Milburn (KLM) scheme. We introduce adaptive teleportation, i.e., such that the choice of entangled state used in the next teleportation depends on the results of the measurements performed during the previous teleportations. We show that adaptive teleportation enables an increase in the probability of faithful multiple teleportation in the KLM scheme. In particular if a qubit is to be teleported more than once then it is better to use nonmaximally entangled states than maximally entangled ones in order to achieve the highest probability of faithful teleportation.

We examine structural and dynamical properties of quantum resonances associated with an avoided crossing and identify the parameter shifts where these properties attain extreme values. Thus the concept of avoided crossing resonance can be defined in different ways, which do not coincide in the general case. These definitions are applied to optimize the fidelity and speed of trapped-ion quantum gates.

We suggest a method of entangling significantly the distant ends of a spin chain using minimal control. This entanglement between distant individual spins is brought about solely by exploiting the dynamics of an initial mixed state with Néel order if the lattice features nearest-neighbor $XXZ$ interaction. There is no need to control single spins or to have engineered couplings or to pulse globally. The method only requires an initial nonadiabatic switch (a quench) between two Hamiltonians followed by an evolution under the second Hamiltonian. The scheme is robust to randomness of the couplings as well as the finiteness of an appropriate quench and could potentially be implemented in various experimental setups, ranging from atoms in optical lattices to Josephson-junction arrays.

We have produced ultracold heteronuclear ${\text{YbRb}}^{\ast }$ molecules in a combined magneto-optical trap by photoassociation. The formation of electronically excited molecules close to the dissociation limit was observed by the trap loss spectroscopy in mixtures of ${}^{87}\text{R}\text{b}$ with ${}^{174}\text{Y}\text{b}$ and ${}^{176}\text{Y}\text{b}$. The molecules could be prepared in well-defined rovibrational levels, allowing for an experimental determination of the long-range potential in the electronically excited state.

We derive analytical solutions for the system of two ultracold spin-polarized fermions interacting in $p$ wave and confined in an axially symmetric harmonic trap. To this end we utilize $p$-wave pseudopotential with an energy-dependent scattering volume. This allows to describe the scattering in tight trapping potentials in the presence of scattering resonances. We verify predictions of the pseudopotential treatment for some model interaction potential obtaining an excellent agreement with exact energy levels. Then we turn to the experimentally relevant case of neutral atom interactions in the vicinity of a $p$-wave Feshbach resonance. In the framework of the multichannel quantum-defect theory we derive relatively simple formula for an energy-dependent scattering volume, and later we apply it to investigate the energy spectrum of trapped atoms close to the $p$-wave Feshbach resonance.

Electron and positron cross sections have been investigated experimentally for scattering from benzotrifluoride $\left({\text{C}}_6{\text{H}}_5{\text{CF}}_3\right)$ molecules over the energy range 0.2–1000 eV. The current results have been compared with our previous results for ${\text{C}}_6{\text{H}}_6$ molecules. Similar to ${\text{C}}_6{\text{H}}_6$, a peak has been observed in electron total cross sections (TCS) centered at 8.0 and a shoulder at about 40 eV. Vibrational excitation cross section experiments were carried out to probe the origin and nature of the 8 eV peak. For positron TCS, a broad peak spanning the region 0.8–15 eV and a change in slope at about 40 eV are observed with the only difference between the current results and those of ${\text{C}}_6{\text{H}}_6$ observed in the region 1–100 eV.

We present absolute differential cross sections (DCS) for elastic scattering from two benzene derivatives ${\text{C}}_6{\text{H}}_5{\text{CH}}_3$ and ${\text{C}}_6{\text{H}}_5{\text{CF}}_3$. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles $15°–130°$ and impact energies 1.5–200 eV. DCS results for these two molecules were compared to those of ${\text{C}}_6{\text{H}}_6$ from our previous study. We found that (1) these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5–200 eV, although DCS for ${\text{C}}_6{\text{H}}_5{\text{CF}}_3$ increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and (2) that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV.

The present work is a generalization of the dynamical screening factor presented by Lo et al. [J. Phys. B 40, 3973 (2007)] to consider an atom located at an arbitrary position within the fullerene. A more elaborate investigation into the case where the atom is located at the center is performed and compared with quantum-mechanical calculations for dynamical screening factors of $\text{Ar}@{\text{C}}_{60}$ [M. E. Madjet et al., Phys. Rev. Lett. 99, 243003 (2007)] and $\text{Mg}@{\text{C}}_{60}$ [H. S. Chakraborty et al., Phys. Rev. A 78, 013201 (2008)]. The $\pi$ and $\sigma$ plasmons of the fullerene are accounted for in a modified screening factor to improve correspondence with the quantum calculations. The spatial dependence of the screening factor was explored with $\text{Ar}@{\text{C}}_{60}$ and $\text{Ar}@{\text{C}}_{240}$ and found to depend significantly on the radial distance of the atom from the center of the fullerene. A spatial averaging of the screening factor is presented.

In this paper we investigate the single and double ionization signals of ${\text{H}}_2$ molecules, with fixed and moving nuclei, as a function of laser intensity, for two different values of laser wavelength ($\lambda =390\text{nm}$ and $\lambda =780\text{nm}$), using an approach for evaluating the ionization signals which allows the investigation of relatively long-lasting pulses. The He system is first investigated to benchmark our calculation against already known results. We confirm the evidence of nonsequentiality in the ionization processes of all the systems investigated. Furthermore, we show that the nuclei motion enhances the double ionization signals by means of a mechanism which is very similar to a charge-resonant enhanced ionization (CREI) effect [Zuo and Bandrauk, Phys. Rev. A 52, R2511 (1995)].