Bound entangled states are states that are entangled but from which no entanglement can be distilled if all parties are allowed only local operations and classical communication. However, in creating these states one needs nonzero entanglement resources to start with. Here, the entanglement of two distinct multipartite bound entangled states is determined analytically in terms of a geometric measure of entanglement and a related quantity. The results are compared with those for the negativity and the relative entropy of entanglement.

We present a protocol for transfer of an unknown quantum state. The protocol is based on a two-mode cavity interacting dispersively in a sequential manner with three-level atoms in the $\Lambda$ configuration. We propose a scheme for quantum networking using an atomic channel. We investigate the effect of cavity decoherence in the entire process. Further, we demonstrate the possibility of an efficient quantum memory for arbitrary superposition of two modes of a cavity containing one photon.

Explicitly correlated Gaussian functions allow an accurate determination of wave functions and energies of a few electron atoms. A recently introduced variant of these functions involving terms linear in the interparticle distances exhibits a faster convergence and correct behavior at coalescence points as shown in pilot calculations for the helium atom. The extension of this method to atoms with more than two electrons requires dealing with a different type of three-electron integral. In this work, we study in detail a generating three-electron integral $\int \exp \left(-{\sum }_{i,j=1}^3{a}_{ij}{\mathbf{r}}_i·{\mathbf{r}}_j\right)∕\left(r_1{r}_2{r}_3\right)d{\mathbf{r}}_{1}d{\mathbf{r}}_{2}d{\mathbf{r}}_3$, present a compact analytical form, and analyze its numerical evaluation.

We show how the scattering phase shift, the $s$-wave scattering length, and the $p$-wave scattering volume can be obtained from Riccati equations derived in variable phase theory. We find general expressions that provide upper and lower bounds for the scattering length and the scattering volume. We show how, in the framework of the variable phase method, Levinson’s theorem yields the number of bound states supported by a potential. We report results from a study of the heteronuclear alkali-metal dimers NaRb and LiRb. We consider ab initio molecular potentials for the $X{}^1\Sigma ^{+}$ and $a{}^3\Sigma ^{+}$ states of both dimers and compare and discuss results obtained from experimentally based $X{}^1\Sigma ^{+}$ and $a{}^3\Sigma ^{+}$ potentials of NaRb. We explore the mass dependence of the scattering data by considering all isotopomers and we calculate the numbers of bound states supported by the molecular potentials for each isotopomer.

The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of a single ${}^3\mathrm{He}$ atom bound to a cluster with $N$ ${}^4\mathrm{He}$ atoms, with the aim of establishing the most adequate filling ordering of single-fermion orbits to the mixed clusters with a large number of ${}^3\mathrm{He}$ atoms. The resulting ordering looks like the rotational spectrum of a diatomic molecule, being classified only by the angular momentum of the level, although vibrational-like excitations appear at higher energies for sufficiently large $N$.

We have measured the ac Stark shift of the $4s^2{}^{1}S_0–4s4p{}^{3}P_1$ line in ${}^{40}\mathrm{Ca}$ for perturbing laser wavelengths between $780\mathrm{nm}$ and $1064\mathrm{nm}$ with a time domain Ramsey-Bordé atom interferometer. We found a zero crossing of the shift for the $m_S=0–m_P=0$ transition and $\sigma$ polarized perturbation at $800.8\left(22\right)\mathrm{nm}$. The data was analyzed by a model deriving the energy shift from known transition wavelengths and strengths. To fit our data, we adjusted the Einstein $A$ coefficients of the $4s3d{}^{3}D–4s4p{}^{3}P$ and $4s5s{}^{3}S–4s4p{}^{3}P$ fine structure multiplets. With these we can predict vanishing ac Stark shifts for the ${}^{1}S_{0}m=0–{}^{3}P_{1}m=1$ transition and ${\sigma }^{-}$ light at $983\left(12\right)\mathrm{nm}$ and at $735.5\left(20\right)\mathrm{nm}$ for the transition to the ${}^{3}P_0$ level.

Self-consistent excited states of condensates are solutions of the Gross-Pitaevskii (GP) equation and have been amply discussed in the literature and related to experiments. By applying a recently introduced more general mean field which includes the GP one as a special case, we find a new class of self-consistent excited states. In these states macroscopic numbers of bosons reside in different one-particle functions, i.e., the states are fragmented. Still, a single chemical potential is associated with the condensate. A numerical example is presented, illustrating that the energies of the new, fragmented states are much lower than those of the GP excited states, and that they are stable to variations of the particle number and shape of the trap potential.

The coherence properties of a $46.9\text{−}\mathrm{nm}$ soft-x-ray laser beam produced in a capillary discharge plasma have been investigated. The beam is produced in a regime that is free from the effect of refraction defocusing, with a divergence of only $0.5–0.6\mathrm{mrad}$. The discharge plasma is produced in capillary channels with length of $45\mathrm{cm}$, where the Fresnel number of the gain medium is of the order of unity. The full laser energy is about $300\mu \mathrm{J}$. The spatial coherence of the laser has been experimentally investigated using a Young’s double-slit interferometer and analyzed assuming a Gaussian Schell-model source and the generalized Van Cittert–Zernike theorem. We demonstrate the achievement of almost full spatial coherence and a near-Gaussian intensity distribution.

Quantum feedback in strongly coupled systems can probe a regime where one quantum of excitation is a large fluctuation. We present theoretical and experimental studies of quantum feedback in an optical cavity QED system. The time evolution of the conditional state, following a photodetection, can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured in a new steady state and then released. The feedback protocol requires resonance operation, and proper amplitude and delay for the change in the drive. We demonstrate the successful use of feedback in the suppression of the vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return to steady state. The feedback works only because we have an entangled quantum system, rather than an analogous correlated classical system.

We investigate theoretically the molecular yield in photoassociation of Bose-Einstein condensed sodium atoms for light intensities of the order of and above those applied in a recent experiment. Our results show that the rate at which ground-state molecules may be formed saturates at high light intensities whereas the loss rate of condensate atoms does not. This is caused by the opposing roles of the short- and long-range pair correlations present near resonance under the influence of the laser and is crucial for the development of efficient photoassociation procedures in a condensate.

We characterize the long-time projective behavior of the stochastic master equation describing a continuous, collective spin measurement of an atomic ensemble both analytically and numerically. By adding state-based feedback, we show that it is possible to prepare highly entangled Dicke states deterministically.

We present a model to realize a probabilistic conditional sign flip gate using only linear optics. The gate operates in the space of number-state qubits and is obtained by a nonconventional use of the teleportation protocol. Both a destructive and a nondestructive version of the gate are presented. In the former case an Hadamard gate on the control qubit is combined with a projective teleportation scheme mixing control and target. The success probability is $1∕2$. In the latter case we need a quantum encoder realized via the interaction of the control qubit with an ancillary state composed of two maximally entangled photons. The success probability is $1∕4$.

A key element in the architecture of a quantum-information processing network is a reliable physical interface between fields and qubits. We study a process of entanglement transfer engineering, where two remote qubits respectively interact with an entangled two-mode continuous-variable (CV) field. We quantify the entanglement induced in the qubit state at the expenses of the loss of entanglement in the CV system. We discuss the range of mixed entangled states which can be obtained with this setup. Furthermore, we suggest a protocol to determine the residual entangling power of the light fields inferring, thus, the entanglement left in the field modes which, after the interaction, are no longer in a Gaussian state. Two different setups are proposed: a cavity-QED system and an interface between superconducting qubits and field modes. We address in detail the practical difficulties inherent in these two proposals, showing that the latter is promising in many aspects.

The dissociative recombination (DR) of $\mathrm{He}{\mathrm{H}}^{+}$ is studied using the multichannel quantum defect theory (MQDT) of molecules. The MQDT is extended to include the dissociative Rydberg states. The idea of a “closed dissociative channel” is introduced for a precise description. The calculated DR cross section sensitively depends upon rotational motion, which enhances the DR at a collision energy lower than $0.2\mathrm{eV}$. Calculations in the present study reproduced the DR rate coefficient measured by two facilities of storage rings (CRYRING and TARN II). A great change of the adiabatic quantum defect with internuclear distance induced a large DR cross section in the noncrossing system. This mechanism is an alternative to the electronic resonance of the crossing existing system.

A high-resolution photoabsorption spectrum of $\mathrm{Ne}$ has been measured in the energy range of the $\left[1s2p\right]n\ell n^{\prime }{\ell }^{\prime }$ doubly excited states, where square brackets indicate hole states, by means of photoion yield spectroscopy. The observed features have been interpreted by adopting a simple Rydberg formula. Energies as well as quantum defects for the members of the $\left[1s2p\right]\left({}^{3,1}P\right)3pnp$ $\left(3⩽n⩽5\right)$ series have been determined. We report observations of angle-resolved spectra of the resonant Auger (RA) transitions to the ${\mathrm{Ne}}^{+}$ $\left[2p^3\right]3p^2$ states and to the ${\mathrm{Ne}}^{+}$ $\left[2s2p^2\right]3p^2$ states from the $\left[1s2p\right]\left({}^{3,1}P\right)3p^2$ doubly excited states. These double-spectator-type transitions are confirmed by a good general agreement between the measured and theoretical RA spectra, where theoretical spectra are calculated based on the Hartree-Fock approximation. The measured anisotropy parameters are compared with theoretical predictions calculated using a pure $LS$ coupling approach. We have made assignments for several levels with the aid of theoretical calculations.

The time-dependent close-coupling theory is extended to allow the calculation of $e-\mathrm{H}$ elastic and inelastic scattering processes. We first calculate ${}^{1,3}S$ elastic scattering cross sections for $\mathrm{H}\left(1s\right)$ in time-dependent Hartree-Fock theory and find good agreement with time-independent distorted-wave theory. We then calculate elastic scattering cross sections for $\mathrm{H}\left(1s\right)$ using time-dependent close-coupling theory and find good agreement with R-matrix scattering theory. Finally, we apply the time-dependent close-coupling method to calculate elastic and inelastic cross sections for $\mathrm{H}\left(2s\right)$ and $\mathrm{H}\left(2p\right)$. Correlation effects are found to be important in all elastic and inelastic processes involving the $n=2$ excited states of hydrogen. In particular, the ionization cross sections are used to calculate ionization rate coefficients for comparison with rate coefficients currently used in collisional-radiative models.

We exploit a method to precisely calibrate the peak intensity of intense laser pulses by measuring the momentum transferred to the ion in single ionization by circularly polarized light. Using this approach, we show how the experimental data can be used to get information about the absolute ionization rate at a specific local laser-peak intensity within the focal volume. The results of this method are compared to other results obtained with different methods of laser-peak-intensity calibration described in the literature.

We study the propagation of sound waves in a Bose-Einstein condensate trapped in a one-dimensional optical lattice. We find that the velocity of the propagation of sound wave packets decreases with increasing optical lattice depth, as predicted by the Bogoliubov theory. The strong interplay between nonlinearities and the periodicity of the external potential generates phenomena that are not present in the uniform case. Shock waves, for instance, can propagate slower than sound waves, due to the negative curvature of the dispersion relation. Moreover, nonlinear corrections to the Bogoliubov theory appear to be important even with very small density perturbations, inducing a saturation of the amplitude of the sound signal.

We have developed a scheme to measure the optical torque exerted by a laser beam on a phase object by measuring the orbital angular momentum of the transmitted beam. The experiment is a macroscopic simulation of a situation in optical tweezers, as orbital angular momentum has been widely used to apply torque to microscopic objects. A hologram designed to generate ${\mathrm{LG}}_{02}$ modes and a CCD camera are used to detect the orbital component of the beam. Experimental results agree with theoretical numerical calculations, and the strength of the orbital component suggest its usefulness in optical tweezers for micromanipulation.

We present a calculation of coherent backscattering with inelastic scattering by saturated atoms. We consider the scattering of a quasimonochromatic laser pulse by two distant atoms in free space. By restricting ourselves to scattering of two photons, we employ a perturbative approach, valid up to second order in the incident laser intensity. The backscattering enhancement factor is found to be smaller than two (after excluding single scattering), indicating a loss of coherence between the doubly scattered light emitted by both atoms. Since the undetected photon carries information about the path of the detected photon, the coherence loss can be explained by a which-path argument, in analogy with a double-slit experiment.