It is established that the mutual coherence of two radiating atoms may be increased using an incoherent pump. This surprising effect derives from a modification of the atomic populations in the two-atom Dicke basis.

Squeezing effects in the resonance fluorescence of a bichromatically driven two-level atom are investigated. Unusual squeezing properties appear in comparison to the monochromatic driving field cases. It is demonstrated that these properties are strongly correlated to two-photon-emission processes, which play an important role in the resonance fluorescence of a bichromatically driven two-level atom.

We use differential forms to derive the quantum-mechanical potential induced by surface curvature. Two surfaces are modeled with the classical Monge representation and the resulting modifications to the potential- and kinetic-energy operators in the Schrödinger equation are obtained. We find that the ground-state energy shift resulting from the dot’s surface curvature is of sufficient order to be observable in quantum nanostructures.

The standard perturbation theory for time-dependent problems in quantum mechanics is reconsidered through renormalization-group methods. This approach justifies a posteriori the theory of quantum resonance given by the multiple-scale analysis of the perturbation series applied to the coupled equations of wave-function amplitudes. The resonance equations for the leading-order amplitude probabilties are then obtained up to second order and a general method for the algorithmic computation of higher-order terms of the perturbation series is given. The three-level model in a monochromatic wave with two resonant states is discussed in the light of the present results.

A recent paper of Gardiner [Phys. Rev. A 56, 1414 (1997)] introduces a particle-number-conserving Bogoliubov method for the excitation spectrum of a Bose-condensed gas, for use in theories of recently experimentally produced trapped atomic Bose condensates. Gardiner’s approach is compared and contrasted with the 1959 Girardeau-Arnowitt theory [Phys. Rev. 113, 755 (1959)], to which it is closely related and which is also fully number conserving. The number-conserving Bogoliubov quasiparticle operators of the Girardeau-Arnowitt theory satisfy Bose commutation relations exactly so long as states with the condensate totally depleted are neglected, whereas those of Gardiner satisfy Bose commutation relations only in an approximation that deteriorates progressively as the condensate is depleted.

We propose two feasible experimental studies of the interaction of light with linearly accelerating media. First, sidebands are induced in the output spectrum of a Mach-Zehnder interferometer when a dielectric in one arm is oscillated parallel to the beam. Second, linear acceleration of a dielectric in a ring cavity will induce asymmetry in the near-resonant optical response profile. Both experiments probe the interaction of photons with inertia by testing the covariant formulation of Maxwell’s equations used here and so the related assumption that the local optical properties of a medium are unaffected by acceleration. The second experiment is explicitly sensitive to a Doppler shift induced when light propagates through linearly accelerating media, predicted by Tanaka [Phys. Rev. A 25, 385 (1982)]. Observation of this Doppler shift would confirm a manifestation of the coupling between radiation and matter in a noninertial context.

This paper considers the Schrödinger propagator on a cone with the conical singularity carrying magnetic flux (“flux cone”). Starting from the operator formalism, and then combining techniques of path integration in polar coordinates and in spaces with constraints, the propagator and its path integral representation are derived. The approach shows that effective Lagrangian contains a quantum correction term and that configuration space presents features of nontrivial connectivity.

An approach is developed for constructing simple analytical formulas accurately approximating solutions to eigenvalue problems of quantum mechanics. This approach is based on self-similar approximation theory. In order to derive interpolation formulas valid in the whole range of parameters of considered physical quantities, the self-similar renormalization procedure is complemented here by boundary conditions which define control functions guaranteeing correct asymptotic behavior in the vicinity of boundary points. To emphasize the generality of the approach, it is illustrated by different problems that are typical for quantum mechanics, such as anharmonic oscillators, double-well potentials, and quasiresonance models with quasistationary states. In addition, the nonlinear Schrödinger equation is considered, for which both eigenvalues and wave functions are constructed.

We propose the Aharonov-Casher (AC) effect for four entangled spin-$\frac{1}{2}$ particles carrying magnetic moments in the presence of impenetrable line charge. The four-particle state undergoes an AC phase shift in two causally disconnected regions, which can show up in the correlations between different spin states of distant particles. This correlation can violate Bell’s inequality, thus displaying the nonlocality for four-particle entangled states in an objective way.

While Kohn-Sham theory uses the quantum-mechanical operator for kinetic energy, Thomas-Fermi theory replaces this with an effective local potential. If both theories are based on the exact universal density functional defined by Hohenberg-Kohn theory, it is an interesting question whether they should give the same results for $N$-electron ground states. This question is examined and answered in the negative. The inconsistency is resolved only by extending the definition of functional derivatives to encompass linear operators. An exact theory must incorporate one-electron energies and occupation numbers derived from Kohn-Sham theory.

An experiment to observe parity nonconservation using the $|{5p}^{6}6s{〉}_{1/2}\to |{5p}^{6}5d{〉}_{3/2}$ transition in ${\mathrm{Ba}}^{+}$ has been proposed [N. Fortson, Phys. Rev. Lett., 70, 2383 (1993)]. We have carried out relativistic configuration-interaction calculations to explore whether the $|{5p}^{6}6s{〉}_{1/2}\to |{5p}^{6}5d{〉}_{5/2}$ and $|{6p}^{6}7s{〉}_{1/2}\to |{6p}^{6}6d{〉}_{5/2}$ transitions in ${\mathrm{Ba}}^{+}$ and ${\mathrm{Ra}}^{+}$ respectively are good candidates for carrying out similiar experiments to measure the nuclear anapole moment. Our results suggest that ${\mathrm{Ra}}^{+}$ might be a good candidate for such an experiment.

A Floquet-Bloch analysis of intense-field photoemission of electrons from a model crystal surface is carried out. Simulations of electron emission spectra as a function of the laser intensity show several phenomena, including (a) the appearance of a sequence of emission bands, separated by bands of zero currents, at an interval of the photon energy, (b) a broad modulation of the envelope of the emission spectrum, and (c) the appearance of subbands within an emission band. The results are discussed and interpreted in terms of the field-modified band structure of the system. A comparison of the Floquet-Bloch model and the popular free-electron Sommerfeld model for intense-field photoeffect is made and the difference is shown to be of qualitative significance.

We have produced a laser-cooled ion crystal in a linear Paul trap containing several hundred ${\mathrm{Ca}}^{+}$ ions. A portion of the ions can be excited by an additional laser to a long-lived metastable energy level that decouples them from the cooling laser radiation. The light pressure acting upon the remaining laser-cooled ions forces them into the direction of the laser beam, while the ions in the metastable state drift to the crystal side that points toward the cooling laser. Depending on the number of ions in the crystal and on the fraction of the excited ions, the spatial separation of the ions in the metastable state and the ions in the cooling cycle can be as large as several hundred micrometers.

We present calculations of the differential scattering cross section for laser-assisted, low-energy electron-potential scattering in a ${\mathrm{CO}}_2$ laser field. We consider the scattering geometry in which the polarization vector of the laser field is parallel to the incident electron momentum. Our results have been obtained by numerically solving the Floquet-Lippmann-Schwinger equation for the Yukawa (screened Coulomb) and the Buckingham polarization potentials as well as the electron-atomic hydrogen static-direct potential. We find that for the geometry and the laser intensities considered, the Kroll and Watson low-frequency approximation gives a good approximation for the differential cross section, even for scattering in the forward direction.

We report a strong dependence of the soft-x-ray spectra generated by high harmonic emission on the chirp of the excitation pulse, when an ultrashort laser drives the process. For identical pulse durations, distinct harmonic peaks can be observed for positively chirped excitation pulses, while for negatively chirped pulses, the harmonic peaks become irregular. This behavior is explained by simulations that combine the chirp of the laser with the intrinsic phase shift of the harmonics. This work resolves an outstanding discrepancy between theory and experiment by demonstrating that high-order harmonic generation driven by short-duration pulses can result in distinct harmonic peaks. This work conclusively demonstrates the role of the intrinsic phase in determining harmonic emission spectra, and control this phase during the emission process.

We report the observation of the first ten collective parametric resonances of an uncooled $N_2^{+}$ ion cloud in a Paul trap driven at simple fractions of twice the secular frequency of the trap by an additionally applied quadrupole field. The fractional resonances are observable only if the excitation field surpasses a critical strength. Odd-even staggering of the thresholds is observed.

In the presence of a static magnetic field, atoms moving in an electromagnetic field with a polarization gradient are bunched around a few momenta that are located on a lattice in momentum space. We show how to construct this lattice in two and three dimensions and present an experiment performed with cesium atoms that gives results that are in excellent agreement with the theoretical predictions.