The temporal evolution of coherent population trapping (CPT) was observed in rubidium atomic vapor when sudden changes were made to the detuning of a weak Raman field. The subsequent creation and destruction of CPT are caused by the temporal oscillations of optically induced Raman coherence, with their period depending on the Raman detuning. The oscillating signal was observed over a time of order of tens of milliseconds, and the dependence of the relaxation time on the cell temperature and laser power were investigated. The main features of the experimental observations were well explained by the time-dependent density-matrix equations.

A theory for the refractive-index enhancement due to quantum coherence and interference has been developed in dispersive polaritonic and photonic band-gap materials doped with an ensemble of noninteracting three-level atoms. Quantum coherence is introduced by driving the atoms with a coherent monochromatic laser field. The real and the imaginary parts of the susceptibility have been calculated by using the master equation and the Laplace transform methods. It is found that the energy gap in these materials plays an important role in the refractive-index enhancement. Numerical simulations for the real and the imaginary parts of susceptibility are performed for SiC as a function of the probe laser frequency. It is found that there is a giant refractive-index enhancement with vanishing absorption when the resonance frequencies lie near the lower band edge.

The Casimir force between metallic plates made of realistic materials is evaluated for distances in the nanometer range. A spectrum over real frequencies is introduced and shows narrow peaks due to surface resonances (plasmon polaritons or phonon polaritons) that are coupled across the vacuum gap. We demonstrate that the Casimir force originates from the attraction (repulsion) due to the corresponding symmetric (antisymmetric) eigenmodes, respectively. This picture is used to derive a simple analytical estimate of the Casimir force at short distances. We recover the result known for Drude metals without absorption and compute the correction for weakly absorbing materials.

We report the observation of polaritonic bistability in semiconductor microcavities in the strong-coupling regime. The origin of bistability is the polariton-polariton interaction, which gives rise to a Kerr-like nonlinearity. The experimental results are in good agreement with a simple model taking transverse effects into account.

We study the dynamics of quantum correlations in a class of exactly solvable Ising-type models. We analyze in particular the time evolution of initial Bell states created in a fully polarized background and on the ground state. We find that the pairwise entanglement propagates with a velocity proportional to the reduced interaction for all the four Bell states. Singletlike states are favored during the propagation, in the sense that tripletlike states change their character during the propagation under certain circumstances. Characteristic for the anisotropic models is the instantaneous creation of pairwise entanglement from a fully polarized state; furthermore, the propagation of pairwise entanglement is suppressed in favor of a creation of different types of entanglement. The “entanglement wave” evolving from a Bell state on the ground state turns out to be very localized in space time. Our findings agree with a recently formulated conjecture on entanglement sharing; some results are interpreted in terms of this conjecture.

We present a theory of the linear response of a Bose-Einstein-condensed gas to external perturbations at finite temperature. The theory developed here is the basis of a recent quantitative explanation of the measurements of condensate excitations and decay rates made at JILA [D. S. Jin et al., Phys. Rev. Lett. 78, 764 (1997)]. The formalism is based on a dynamic, number-conserving, mean-field scheme and is valid in the collisionless limit of well-defined quasiparticles. The theory is gapless, consistent with the generalized Kohn theorem for the dipole modes, and includes the time-dependent normal and anomalous averages, Beliaev and Landau processes, and all relevant finite-size effects. The important physical process where the thermal cloud is driven directly by the external perturbation is explicitly included. This is required for consistency with the dipole modes and is also needed to explain the JILA observations.

We consider the class of the one-mode Gaussian states of the quantum radiation field. The relative entropy of such a state with respect to a similar one is derived. We analyze the entropic amount of nonclassicality of a Gaussian state defined as the minimal relative entropy of any classical Gaussian state with respect to it. A similar quantity built with the Hilbert-Schmidt distance is also calculated. Both nonclassicality measures are then compared with the Bures-metric degree of nonclassicality evaluated previously. The properties of the closest classical Gaussian state, as well as the decrease of the nonclassicality under thermal noise mappings are carefully examined in each case. For mixed states we find that only the Bures-distance amount of nonclassicality is equivalent to the nonclassical depth.

It has been proposed that the radio-frequency electric-dipole $\mathrm{}\left(E1\mathrm{}\right)\mathrm{}$ transition between two nearly degenerate opposite-parity states in atomic dysprosium should be highly sensitive to possible temporal variation of the fine-structure constant $\left(\alpha \right)$ [V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A 59, 230 (1999)]. We analyze here an experimental realization of the proposed search in progress in our laboratory, which involves monitoring the $E1\mathrm{}$ transition frequency over a period of time using direct frequency counting techniques. We estimate that a statistical sensitivity of $|\dot{\alpha }/\alpha |\sim {10}^{-18}/\mathrm{yr}$ may be achieved and discuss possible systematic effects that may limit such a measurement.

Total cross sections for electron-ion photorecombination (PR) processes are calculated using a projection-operator and resolvent-operator approach. This approach provides a unified quantum-mechanical description of the combined electron-ion PR process, including radiative and dielectronic recombination as coherent, interfering components. An especially adapted version of the Hebrew-University Lawrence-Livermore Atomic Code HULLAC is developed and employed for the calculations. In particular, PR cross sections for He-like argon and iron ions are calculated for incident-electron energies in the vicinity of the ${1s2l2l}^{\prime }$ and ${1s2l3l}^{\prime }$ doubly-excited, autoionizing levels of the Li-like ions. Significant effects of quantum interference between radiative and dielectronic recombination, in the form of asymmetric PR cross-section profiles, are predicted, especially for weak transitions. The general behavior of the interference effect, as a function of the ion charge q and as a function of the principal quantum number $n^{\prime }$ of the outer electron in the autoionizing state, is investigated using a hydrogenic-scaling analysis. It is found that the degree of asymmetry in the PR cross-section profile can be substantial for close-to-neutral ions and also for very highly-charged ions. In the intermediate-charge regime, on the other hand, the asymmetry is anticipated to be less prominent. The dependence of the quantum-interference effect on $n^{\prime }$ is predicted to be much weaker.

We study the mechanisms of collapse of the condensate wave function in the Gross-Pitaevskii theory with attractive interparticle interaction. We reformulate the Gross-Pitaevskii equation as Newton’s equations for a flux of particles, and introduce the collapsing fraction of particles. We assume that this collapsing fraction is expelled from the condensate due to dissipation. Using this hypothesis we analyze the dependence of the collapse behavior on the initial conditions. We find that, for a properly chosen negative scattering length, the remnant fraction of atoms becomes larger when the initial aspect ratio of the condensate is increased.

We examine the effect of the transverse breathing mode on the longitudinal sound propagation in a Bose-Einstein condensate in a one-dimensional optical lattice. In particular, we discuss how the coupling with the transverse breathing mode influences the sound velocity in an optical lattice. Using a variational approach we calculate the dispersion relations for the longitudinal sound mode and the transverse breathing mode analytically, and find that the shift in the sound velocity from the uncoupled result can be large enough to be experimentally relevant. We also find that the effective mass of the transverse breathing mode is affected considerably by the coupling to longitudinal sound.

Atomic vapors make flexible and useful nonlinear optical media when light is detuned far from resonances. However, few direct measurements of their nonlinear coefficients have been performed to date. We present a measurement of the Kerr coefficient for various detunings to both the red and blue of the $D2\mathrm{}$ line in hot atomic rubidium vapor. Saturation effects complicate the interpretation of the standard z-scan method, but a simple saturation model agrees well with our data. We find values of $n_2\approx \pm {10}^{-7}{\mathrm{cm}}^2/\mathrm{W}$ for 1 GHz detunings from the $D2\mathrm{}$ line.

We consider a system consisting of a single ion in a Paul trap coupled to a cavity electromagnetic field mode. We analyze the fidelity of a scheme for quantum swapping between vibrational and cavity field states, when the system is in contact with a reservoir at zero temperature.

In this paper we discuss entanglement properties of neutral kaons systems and their use for testing local realism. In particular, we analyze a Hardy-type scheme [A. Bramon and G. Garbarino, Phys. Rev. Lett. 89, 160401 (2002)] recently suggested for performing a test of hidden-variable theories against standard quantum mechanics. Our result is that this scheme could, in principle, lead to a conclusive test of local realism, but only if higher identification efficiencies than in today’s experiments will be reached.

We compare the maximum achievable polarization correlations for classical-like separable states and quantum entangled states. For one-photon systems we find that the maximally entangled states have three times larger correlations than the maximum correlations achievable with separable states. However, for larger photon numbers we find that there are separable states with larger correlations than the maximally entangled states.

We present an analytical response theory formulation for the dependence of the nuclear magnetic resonance shielding tensor of molecules on the external magnetic field. First-principles calculations for ${}^{59}\mathrm{Co}$ in $\mathrm{Co}(\mathrm{acetylacetonate}{)}_3$ and $\mathrm{Co}({\mathrm{NH}}_3{)}_6^{3+}$ are carried out using the Hartree-Fock self-consistent field method as well as density-functional theory. We report magnetic-field dependence of the ${}^{59}\mathrm{Co}$ shielding constant of $-6\times {10}^{-3}{\mathrm{p}\mathrm{p}\mathrm{m}/\mathrm{T}}^2$ in $\mathrm{Co}(\mathrm{acetylacetonate}{)}_3,$ which is at the limit of being experimentally observable.

Variational calculations of the ground-state energy of helium are performed using a basis set representation that includes an explicit treatment of the Fock expansion in hyperspherical coordinates. The construction of basis functions that have the correct cusp behavior at three-particle coalescence points and the evaluation of integrals containing these functions is discussed. The basis set in hyperspherical coordinates is added to a basis set consisting of products of Laguerre polynomials in perimetric coordinates. It is demonstrated that the use of Fock basis functions provides a substantial improvement in the convergence rate of the basis set expansion.

We report equilibrium geometric structures of ${\mathrm{CuO}}_2,$ ${\mathrm{CuO}}_3,$ ${\mathrm{CuO}}_6,$ and ${\mathrm{CuO}}_6^{-1}$ clusters obtained by an all-electron linear combination of atomic orbitals scheme within the density-functional theory with generalized gradient approximation to describe the exchange-correlation effects. The vibrational stability of all clusters is examined on the basis of the vibrational frequencies. A structure with $C_s$ symmetry is found to be the lowest-energy structure for ${\mathrm{CuO}}_2,$ while a Y-shaped structure with $C_{2v}$ symmetry is the most stable structure for ${\mathrm{CuO}}_3.$ For the larger ${\mathrm{CuO}}_6$ and ${\mathrm{CuO}}_6^{-1}$ clusters, several competitive structures exist with structures containing ozonide units being higher in energy than those with ${\mathrm{O}}_2$ units. The infrared and Raman spectra are calculated for the stable optimal geometries.

We study hydrogenlike target excitation by a traveling electromagnetic pulse. The spatial size of the pulse $l=c\tau$ $(c$ is the speed of light and $\tau$ is the pulse duration) is assumed to be comparable or less than the characteristic size of the initially occupied atomic state. When propagating through the atom, the pulse is shown to transform the electron wave function “slice by slice.” These transformations lead to electron transitions between states with $\Delta m=\pm 1$ which are forbidden in the dipole approximation. The case of linear polarization is considered. It is found that magnetic-level excitation probabilities are small for the hydrogen atom, but can be more significant for the hydrogenlike multicharged ions.

The possibilities of pairing in two-dimensional boson-fermion mixtures are carefully analyzed. It is shown that the boson-induced attraction between two identical fermions dominates the p wave pairing at low density. For a given fermion density, the pairing gap becomes maximal at a certain optimal boson concentration. The conditions for observing pairing in current experiments are discussed.