Total and partial photoionization cross sections for the ejection of either a $2p$ or a $2s$ electron from the ground ${2s}^2{2p}^4{}^{3}P$ state of atomic oxygen have been investigated using the R-matrix method. Cross sections are dominated by Rydberg series of autoionizing resonances converging to several ionic states. The autoionizing states are analyzed and identified using a procedure of eigenphase gradients. Comparison of our results with available previous calculations and experiments is shown to lead to some interesting conclusions regarding the importance of electron correlation and normalization of the measured relative cross sections. Our calculation removed long-standing discrepancy between theory and experiment regarding the shape of photoionization cross section near the ${}^2{P}^o$ threshold. The calculated branching ratios for the production of ${}^4{S}^o,{}^2{D}^o,$ and ${}^2{P}^o$ states at 584 and $304\hspace{0.5em}\mathrm{\AA }\mathrm{}$ show good agreement with experiments.

A method for calculating resonances in three-body Coulombic systems is proposed. The Faddeev-Merkuriev integral equations are solved by applying the Coulomb-Sturmian separable expansion method. The $e^{-}{e}^{+}{e}^{-}$ S-state resonances up to $n=5\mathrm{}$ threshold are calculated.

We study the reflectivity of Casimir–van der Waals potentials, which behave as $-C_4{/r}^4$ at large distances and as $-C_3{/r}^3$ at small distances. The overall behavior of the reflection amplitude R depends crucially on the parameter $\rho =\sqrt{2M}{C}_3/\left(ħ\sqrt{C_4}\right)$ which determines the relative importance of the $-{1/r}^3$ and the $-{1/r}^4$ parts of the potential. Near threshold, $E={ħ}^2{k}^2/\left(2M\right)\mathrm{}\to 0,$ the reflectivity is given by $|R|\sim \exp \left(-2bk\right),$ with b depending on $\rho$ and the shape of the potential at intermediate distances. In the limit of large energies, $\ln |R|$ is proportional to $-k^{1/3}$ with a known constant of proportionality depending only on $C_3.$ For small values of $\rho ,$ the reflectivity behaves as for a homogeneous $-{1/r}^3$ potential in the whole range of energies and does not depend on $C_4$ or the shape of the potential beyond the $-{1/r}^3$ region. For moderate and large values of $\rho ,$ the reflectivity depends on $C_4$ and on the potential shape. For sufficiently large values of $\rho ,$ which are ubiquitous in realistic systems, there is a range of energies beyond the near-threshold region, where the reflectivity shows the high-energy behavior appropriate for a homogeneous $-{1/r}^4$ potential, i.e., $\ln |R|$ is proportional to $-\sqrt{k}$ with a proportionality constant depending only on $C_4.$ This conspicuous and model-independent signature of the Casimir effect is illustrated for the reflectivities of neon atoms scattered off a silicon surface, which were recently measured by Shimizu [Phys. Rev. Lett. 86, 987 (2001)].

Results of density-functional calculations for atoms in very strong magnetic fields using a two-dimensional finite-element basis set are reported for ground-state energies of helium, carbon, and neon, and for some excited states of helium. We give results obtained by using three different local-density functionals. A comparison with multi-Landau-channel Hartree-Fock calculations shows reasonable agreement for helium.

We investigate the electromagnetic-transition probabilities for the helium atom embedded in a strong magnetic field. In total, approximately 12 000 transitions have been calculated covering a grid of 20 different field strengths in the complete regime $B=0\mathrm{}-100\hspace{0.5em}\mathrm{a}.\mathrm{u}.\mathrm{}$ The changes of the oscillator strengths with increasing field strength are discussed in detail, addressing both individual transitions and sets of transitions among certain symmetry subspaces. A complete reorganization of the oscillator strengths in the intermediate-field regime is observed.

We obtain the gain of the probe field at multiple frequencies in a closed three-level V-type system using a frequency-modulated pump field. There is no associated population inversion among the atomic states of the probe transition. We describe both the steady-state and transient dynamics of this system. Under suitable conditions, the system exhibits a large gain simultaneously at a series of frequencies far removed from resonance. Moreover, the system can be tailored to exhibit multiple frequency regimes where the probe experiences anomalous dispersion accompanied by negligible gain or absorption over a large bandwidth, a desirable feature for obtaining superluminal propagation of pulses with negligible distortion.

The time-dependent survival probabilities of autoionizing $4pNd$ wave packets in calcium have been measured. Femtosecond laser pulses induce sequential isolated-core excitations of singly excited $4sNd$ radial wave packets to create and probe the nonstationary doubly excited states. Stair step rather than exponential decay of the wave packets is observed. Moreover, we show that the autoionization lifetime can be varied by a factor of five by adjusting the relative phases of the constituent eigenstates in the packet. The stair-step decay structure and its dependence on the wave packet phase is interpreted using an intuitive time-domain picture. The experimental results are in excellent agreement with a K-matrix based, 28-channel quantum-defect theory calculation as well as with an approximate two-channel formulation.

The ideas of interference stabilization of Rydberg atoms are adapted to photodissociation and stabilization of molecules by a strong laser field. Multiple strong-field-induced Raman-type transitions between vibrational levels of the ground electronic state are taken into account. For the molecular ion ${\mathrm{H}}_2^{+}$ matrix elements of these transitions are calculated numerically and the arising equations for probability amplitudes to find a molecule at ground-state vibrational levels are solved (a) in stationary and (b) in the initial-value-problem formulations. In the stationary formulation, complex quasienergies and quasienergy zones are found. Specific values of the light frequency $\omega$ are found at which some quasienergy zones narrow with growing light intensity. Such an effect indicates a possibility of stabilization, which is confirmed to occur by a direct solution of the initial-value problem. The calculated total probability of photodissociation per pulse in the dependence on the light peak intensity is shown to decrease its growth with growing light intensity. Dynamics of photodissociation in the stabilization regime and structure of the arising vibrational wave packets are investigated and discussed. The method of description, in which Raman-type vibrational-vibrational transitions are taken into account is compared with that based on the ideas of the field-induced avoided crossing.

We examine waves localized near a boundary between two weakly segregated Bose-Einstein condensates. In the case of a wavelength of the order of or larger than the thickness of the overlap region the variational method is used. The dispersion laws for the two oscillation branches are found in analytic form. The opposite case of a wavelength much shorter than the healing length in the bulk condensate is also discussed.

We propose a scheme to generate and detect various kinds of quantum entanglement in a spin-1 Bose-Einstein condensate. It is shown that substantial many-particle entanglement can be generated directly in the spin-1 condensate by free dynamical evolution with a properly prepared initial state. The scheme also provides a simple method to generate three-mode entanglement in the second-quantization picture and to detect the continuous variable type of entanglement between two effective modes in the spin-1 condensate.

We discuss the dynamics of a Bose-Einstein condensate during its nondestructive imaging. A generalized Lindblad superoperator in the condensate master equation is used to include the effect of the measurement. A continuous imaging with a sufficiently high laser intensity progressively drives the quantum state of the condensate into number squeezed states. Observable consequences of such a measurement-induced squeezing are discussed.

We develop a theory on optical absorption in a dilute Bose-Einstein gas at low temperatures. This theory is motivated by the Bogoliubov theory of elementary excitations for this system, and takes into account explicitly the modification of the nature and dispersion of elementary excitations due to Bose-Einstein condensation. Our results show important differences from existing theories.

In this paper, the influence of dissipation on the dynamics of a recently proposed model [Phys. Rev. A $60,$ 1491 (1999)] of a strongly far-off-resonant pumped Bose-Einstein condensate interacting with a quantized light field is studied. It is verified that dissipation induces an exponential instability in the field mean intensities for values of parameters where the undamped system is stable. Also considered is the impact of dissipation on the quantum-statistical properties of the light and atomic fields.

The dynamics of the interaction of a quantized cavity field and the vibronic degrees of freedom of a trapped ion is studied under realistic conditions by including cavity losses, spontaneous electronic transitions, and atomic nonlinearities. As long as spontaneous electronic transitions are negligible, analytical results are derived for describing the interaction of the trapped ion and the damped cavity field in the secular approximation. Under more general conditions, when the secular approximation breaks down and spontaneous emission effects become important, the dynamics of the system is studied by quantum-trajectory methods. As an example we demonstrate that, by exploiting the nonlinearities inherent in the dynamics of the system, one may prepare correlated vibronic states and vibrational Fock states. Moreover, we study the generation of an entangled Greenberger-Horne-Zeilinger state. Taking into account the decoherence due to electronic and cavity losses, the best fidelity is obtained under conditions far from the Lamb-Dicke regime.

In this paper, synchronization of chaotic oscillations in semiconductor lasers by optical injection in a transmitter-receiver configuration is studied numerically. A chaotic signal is generated from a semiconductor laser with optical feedback in the transmitter and is injected into the receiver laser without optical feedback. We examined the conditions of chaotic synchronization in the system. As a result, we observed complete chaos synchronization within a finite area of very small parameter mismatch between the two laser systems. In addition, chaotic oscillation synchronized by amplification phenomena was observed in the ordinary injection-locking regime with higher optical injection ratios. We demonstrated that synchronization of chaotic oscillations by amplification results from a kind of injection locking under chaotic light injection and is very tolerant to the parameter mismatch between the two lasers, in contrast to the complete synchronization case.

We study localization of atomic position when a three-level atom interacts with a quantized standing-wave field in the Ramsey interferometer setup. Both the field quadrature amplitude and the atomic internal state are measured to obtain the atomic-position information. It is found that this dual-measurement scheme produces an interference pattern superimposed on a diffractionlike pattern in the atomic-position distribution, where the former pattern originates from the state-selective measurement and the latter from the field measurement. The present scheme results in a better resolution in the position localization than the field-alone measurement schemes. We also discuss the measurement-correlated mechanical action of the standing-wave field on the atom in the light of Popper’s test.

The equivalence between the off-diagonal radiative-decay coupling (ODRDC) effect in the bare-atom picture of a three-level atomic system [see Cardimona et al., J. Phys. B 15, 55 (1982)] and the electromagnetically induced transparency (EIT) effect in the dressed-atom picture [see Imamoǧlu et al., Opt. Lett. 14, 1344 (1989)] is uncovered and a full comparison of their physical origins is given. The mechanism for both ODRDC and Harris’ EIT is found to be a consequence of the quantum interference between a direct absorption path and an indirect absorption path mediated by either a self absorption of spontaneous photons or a Fano-type coupling. A connection is then pointed out between the effects of probe-field gain (PFG) based on an ODRDC process [see Huang et al., Phys. Rev. A 64, 013822 (2001)] and amplification without inversion (AWI) [see Fearn et al., Opt. Commun. 87, 323 (1992)] in the bare-atom picture of a three-level atomic system. The PFG effect is found as a result of transferring electrons between the two upper levels due to the phase-sensitive coherence provided by a laser-induced ODRDC process, while the AWI effect to one of the two probe fields is attributed to its coupling to a strong laser field generating an off-resonant gain through an induced nonlinearity in the other probe field. Both the advantages and disadvantages as well as the limitations of the ODRDC, EIT, PFG, and AWI effects are discussed and compared.

The nature of the stochastic process defined by Bohm’s momentum is elucidated for stationary energy eigenstates and nonstationary states in classically nonchaotic and chaotic Hamiltonian systems. In addition, the nature of the stochastic process defined by Bohm’s quantum force is elucidated for stationary energy eigenstates in nonchaotic and chaotic systems, and for nonstationary states in nonchaotic systems. From these results, the following can be concluded. For stationary energy eigenstates, the process defined by the momentum is generically a stationary, Dirac-delta process in both nonchaotic and chaotic systems; in contrast, the process defined by the quantum force is nongeneric. For nonstationary states, the processes defined by the momentum and quantum force are both nongeneric in nonchaotic systems. Furthermore, for nonstationary states, the process defined by the momentum is, with a high level of confidence, a stationary, stable, brown ${(f}^{-2}$ power spectrum) process in the chaotic kicked pendulum. It is conjectured that this is also true for other chaotic systems. The preceding conclusion and conjecture complement those in [Phys. Rev. A 63, 042105 (2001)] for the process defined by the quantum force for nonstationary states in chaotic systems.

We show a new Bell-Clauser-Horne inequality for two entangled three-dimensional quantum systems (so-called qutrits). This inequality is not violated by a maximally entangled state of two qutrits observed through a symmetric three-input- and three-output-port beam splitter only if the amount of noise in the system is greater than $\left(11\mathrm{}-6\sqrt{3}\right)/2\mathrm{}\approx \mathrm{0.308.}$ This result is in a perfect agreement with the previous numerical calculations presented in Kaszlikowski et al. [Phys. Rev. Lett. 85, 4418 (2000)]. Moreover, we prove that for noiseless case, the necessary and sufficient condition for the threshold quantum efficiency of detectors below which there is no violation of local realism for the optimal choice of observables is equal to $6\left(15-4\sqrt{3}\right)/59\mathrm{}\approx \mathrm{0.821.}$ This efficiency result again agrees with the numerical predictions.