This paper shows that under certain symmetry conditions the probability of remaining in the initial state (the probability of no transition) in a chainwise-connected multistate system driven by two or more delayed laser pulses does not depend on the pulse order.

The two-photon ionization of the metal atoms V, Cr, Y, La, and Ir sputtered by an Ar-ion gun from solid targets has been investigated using linearly polarized laser pulses of 500-fs duration and 248.6-nm (KrF) wavelength in combination with mass spectroscopy that is free of volume effects. A near-resonant ionization process has to be attributed to all five atoms. By fitting analytical solutions of a rate equation model describing the temporal evolution of the ionization process, we can determine absolute values of the one-photon cross sections and saturation intensities.

The instability condition of the nonvortex state toward vortex formation is examined within the Bogoliubov theory when a Bose-Einstein condensate is under externally forced rotation. The obtained critical angular velocity combined with the previous stability conditions for a vortex yields a detailed phase diagram in the critical velocity vs the system parameter. This facilitates vortex formation experiments for alkali-metal-atom gases confined in a harmonic potential.

We calculate the decay amplitude of a harmonically trapped Bose-Einstein condensate with attractive interaction via the Feynman path integral. We find that when the number of particles is less than a critical number, the condensate decays relatively slowly through quantum tunneling. When the number exceeds a critical one, a “black hole” opens up at the center of the trap, in which density fluctuations become large due to a negative pressure, and inelastic collisions will drain the particles from the trap. As the black hole is fed by tunneling particles, we have a novel system in which quantum tunneling serves as a hydrodynamic source.

The transmission probability of an ultracold cascade three-level atom through micromaser systems is calculated and analyzed. It is shown that the micromaser systems can be used as velocity selectors for ultracold three-level atoms. The velocity selectivity is better for ultracold three-level atoms than for ultracold two-level atoms, and is better in a two-cavity system than in a one-cavity system.

There are several factors that lead to a huge enhancement of parity and time invariance violating effects in the Ra atom: very close electronic levels of opposite parity, the large nuclear charge $Z,$ and the collective nature of $T,P$-odd nuclear moments. Experiments with radium may be used to measure its nuclear anapole, magnetic quadrupole, and Schiff moments. Such measurements provide information about parity and time invariance violating nuclear forces and electron-nucleon interactions.

We show that the possibility of distinguishing between single- and two-photon detection events, usually not met in the actual experiments, is not a necessary requirement for proof that the experiments of Alley and Shih [Phys. Rev. Lett. 61, 2921 (1988)] and Ou and Mandel [Phys. Rev. Lett. 61, 50 (1988)] are modulo a fair sampling assumption, valid tests of local realism. We also give the critical parameters for the experiments to be unconditional tests of local realism, and show that some other interesting phenomena (involving bosonic-type particle indistinguishability) can be observed during such tests.

We propose a which path quantum eraser scheme based on a recent experiment by Eichmann et al. [Phys. Rev. Lett. 70, 2359 (1993)] involving two four-level atoms. We show that the quantum eraser can be used for the detection of the decoherence time of macroscopic or mesoscopic entangled superpositions of pointer states of a meter with one of the two atoms, by the visibility of the interference pattern.

A new scheme for quantum cryptography, based on a distributed polarization quantum intensity interferometer, is presented. Two-photon entangled states generated via the optical nonlinear process of type-II phase-matched spontaneous parametric down-conversion are used to securely distribute secret cryptographic keys. The high contrast and stability of the quantum interference pattern obtained by using this design renders it superior to the best existing single-photon polarization technique. In addition, the use of high-repetition-rate femtosecond pump pulses for down-conversion significantly enhances the production rate of entangled photon pairs for key distribution.

Quantum information processing is usually associated with a specific computational basis. Nevertheless, for a deeper understanding of the fundamental principles of quantum computing, it is essential to investigate what is the fidelity of universal operations that are basis independent; i.e., the task is to perform optimally a specific operation on a qubit or a quantum register that is in an unknown state. In this paper we introduce the universal-NOT gate that takes as an input a qubit in an arbitrary state $|\Psi 〉$ and generates an output that is as close as possible to the orthogonal state $|{\Psi }^{\perp }〉.$

A procedure is described for the precise nonrelativistic evaluation of the dipole polarizabilities of ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ that avoids any approximation based on the size of the electron mass relative to the nucleus mass. The procedure is constructed so that sum rules may be used to assess the accuracy of the calculation. The resulting polarizabilities are consistent with experiment within the error bars of the measurements and are far more precise than values obtained by other theoretical methods.

We consider the two-point correlation function of the photodissociation cross section in molecules where the fragmentation process is indirect, passing through resonances above the dissociation threshold. In the limit of overlapping resonances, a formula is derived, relating this correlation function to the behavior of the corresponding classical system. It is shown that nonuniversal features of the two-point correlation function may have significant experimental manifestations.

The present paper reports the ab initio evaluation of the electron affinity of oxygen, and the value of its isotope shift. The theoretical results are in good agreement with the recent electron affinity measurements for ${}^{16}\mathrm{O}$ ${\mathrm{and}}^{18}\mathrm{O}$ by photodetachment microscopy, revealing an “anomalous” isotope shift. The theoretical fine structure of the negative ion ${2p}^5{}^2{P}_{1/2-3/2}^o$ is also in very good agreement with observation.

A combined experimental and theoretical study of argon valence photoionization illustrates the discovery of the broad lack of validity of the independent-particle approximation (IPA) for x-ray photoemission. In addition to previously known breakdowns of the IPA, which are limited to high photon energies and regions very near threshold, the observed breakdown in photoionization at intermediate energies demonstrates generally that the IPA is valid only in very restricted domains. These restrictions are expected to be relevant throughout the periodic table, with consequences for a wide variety of applications.

Small doubly charged negative cluster ions ${\mathrm{SiC}}_n^{2-}$ (with $n=6,$ 8, and 10) are produced by sputtering the surface of a SiC specimen with a 14.5-keV ${\mathrm{Cs}}^{+}$-ion beam. They are detected in a double-focusing mass spectrometer that covers a dynamic abundance range of about ${10}^9.$ The emission yields of these dianionic clusters amount to roughly ${10}^{-4}$ of the corresponding singly charged cluster ions. For both types of ion species, the abundance distributions decrease monotonically with an increasing number of C atoms in the cluster. This observation is ascribed to fragmentation processes that are due to the high amount of internal energy relayed to the cluster species in the sputtering event. Apart from this decomposition caused by excitation, the flight time through the mass spectrometer of ∼15 μs establishes a lower limit with respect to the intrinsic lifetimes of both the singly and doubly charged ions.

We recorded constant scaled-energy spectra of helium Rydberg atoms in both electric and magnetic fields in a regime where the hydrogen atom behaves regularly. Jonckheere, Grémaud, and Delande [Phys. Rev. Lett. 81, 2442 (1998)] recently showed that the nearest-neighbor statistics of sufficiently highly excited states follows a $\delta$-Poisson distribution, which depends on the quantum defect $\delta .$ We find global deviations from this $\delta$-Poisson model, which we attribute to the size of the effective Planck constant ${ħ}_{\mathrm{eff}}.$ Significant deviations at small level spacings indicate that the description of level statistics with the $\delta$-Poisson model is incomplete.

We compare the influence of quantum statistics and atom-atom interaction in bright and dark one-dimensional optical lattices for atoms using quantum rate equations. Via a Hartree-Fock–type mean-field approach we derive an effective nonlinear single-atom equation and solve it self-consistently for a prescribed atomic density. Using a simplified dipole-dipole interaction potential, we show that the atomic energy bands are very sensitive to the mean atomic density, even in a parameter regime where temperature and band populations exhibit only a very small density dependence. Bright lattices show energy shifts towards smaller band separations, while the effect is in the opposite direction and smaller for dark lattices. In general, dipole-dipole interaction strongly dominates the influence of quantum statistics, except for very large detunings, where the spontaneous emission rate is very small.

We experimentally and theoretically investigate the coherent response of ${\mathrm{Tm}}^{3+}$ ions in yttrium aluminum garnet (YAG). Working on the ${}^3{H}_6{\mathrm{}\left(1\right)\mathrm{}}^3{H}_4\mathrm{}\left(1\right)\mathrm{}$ transition we observe optical nutation signals that exhibit multiple distinct Fourier components having polarization-dependent frequencies and weights. This phenomenon is caused by the presence of six different transition-dipole moment orientations of ${\mathrm{Tm}}^{3+}$ ions in YAG and a resultant dependence of ion-field coupling on field-propagation direction and polarization. Experimental data shown are in excellent agreement with simulation results based on numerical integration of the Maxwell-Bloch equations.

We report on dynamical simulations of Bose-Einstein condensation via evaporative cooling in an atomic trap. The results show evidence for spontaneous vortex formation and quantum dynamics in small traps.

We discuss excited Bose-condensed states and find the criterion of dynamical stability of a kinkwise state, i.e., a standing matter wave with one nodal plane perpendicular to the axis of a cylindrical trap. The dynamical stability requires a strong radial confinement corresponding to the radial frequency larger than the mean-field interparticle interaction. We address the question of thermodynamic instability related to the presence of excitations with negative energy.