The high-resolution resonant Auger spectra of Br $3d^{-1}np\pi$ $(n=6–9)$ in HBr are presented. These spectra are extremely complex, with very intense shake and vibrational features. Especially surprising is the observation of at least five intense Auger lines for each intermediate state due to transitions into different final-state configurations; this number of lines can only be explained with strong nonmonopole transitions which prevent obtaining information on the symmetry character of the excited-state orbital in the intermediate state. They are explained in a semiclassical model with the interaction between the Auger electron and the excited Rydberg electron.

We develop the eikonal-Volkov approximation (EVA) to describe atomic and molecular strong-field dynamics. The main component of this approach is the approximate solution for the continuum states of one and two electrons in the presence of a long-range ionic potential and a strong laser field. These solutions include the laser field fully, the ionic potential, and the electron-electron interaction in the eikonal approximation, and describe the nonperturbative coupling between these interactions. Comparison with numerically evaluated continuum electron wave functions demonstrates quantitative accuracy of the approximate solutions. Their long-time limit yields the quasienergy (Floquet) states of the continuum electron. We also show how to extend the applicability of these solutions to deal with the singularities of the ionic potential, where straightforward eikonal approximation breaks down. The large-angle scattering (hard collision) is incorporated in the EVA formalism using an expansion in the number of hard collisions. Finally, we describe how the EVA formalism can be used to obtain simple analytical expressions for various strong-field problems.

We consider radiative transport in ultracold atomic systems under conditions of electromagnetically induced transparency. We calculate the macroscopic susceptibility and scattering tensors of the light and show that essential anisotropic optical properties such as dichroism and birefringence naturally appear. In such a case, light propagation through a spatially nonhomogeneous atomic cloud is considered for an arbitrary direction of the probe light. We determine the polarization properties of the coherently transmitted probe light as well as the polarization dependence of light incoherently scattered in an arbitrary direction. Both the steady state regime and time-dependent case are discussed. Concrete calculations are performed for the case of an inhomogeneous and ultracold sample of ${}^{87}\text{R}\text{b}$ atoms.

In this work it is shown how to obtain, in a simple way, localized (nondiffractive) subluminal pulses as exact analytic solutions to the wave equations. These ideal subluminal solutions, which propagate without distortion in any homogeneous linear media, are herein obtained for arbitrarily chosen frequencies and bandwidths, avoiding in particular any recourse to the noncausal (backward moving) components that so frequently plague the previously known localized waves. Such solutions are suitable superpositions of—zeroth order, in general—Bessel beams, which can be performed either by integrating with respect to (w.r.t.) the angular frequency $\omega$, or by integrating w.r.t. the longitudinal wave number $k_z$: Both methods are expounded in this paper. The first one appears to be powerful enough; we study the second method as well, however, since it allows us to deal even with the limiting case of zero-speed solutions (and furnishes a way, in terms of continuous spectra, for obtaining the so-called “frozen waves,” so promising also from the point of view of applications). We briefly treat the case, moreover, of nonaxially symmetric solutions, in terms of higher-order Bessel beams. Finally, some attention is paid to the known role of special relativity, and to the fact that the localized waves are expected to be transformed one into the other by suitable Lorentz transformations. In this work we fix our attention especially on acoustics and optics: However, results of the present kind are valid whenever an essential role is played by a wave equation (such as electromagnetism, seismology, geophysics, gravitation, elementary particle physics, etc.).

We employ a variational technique to describe the propagation of a Gaussian beam in a nonlinear, weakly nonlocal medium and derive the conditions for breathing soliton formation in both one and two transverse dimensions. The reduced one-dimensional results agree quantitatively with known exact nonlocal soliton solutions. We subsequently formulate a simple procedure for estimating the strength of a weak nonlocality and verify its applicability by direct numerical simulations.

We develop a systematic formalism to calculate the correlation functions of fluorescence from a multiatom system into guided modes of a nanofiber. We find that, in the case of a linear array of $N$ atoms, the first- and second-order correlation functions may contain the terms of up to the second and fourth orders of $N$, respectively. We show the possibility of fiber-mediated superfluorescence in the case where the spacing of the atoms in a linear array is an integer multiple of the wavelength of the resonant guided modes. We also study the case of atoms with random positions. We find that the correlation functions have, in general, different behaviors depending on whether the photons are emitted in the same or opposite directions.

Recent numerical results showed that spin chains are able to produce long-distance entanglement (LDE). We develop a formalism that allows the computation of LDE for weakly interacting probes with gapped many-body systems. At zero temperature, a dc response function determines the ability of the physical system to generate genuine quantum correlations between the probes. We show that the biquadratic Heisenberg spin-1 chain is able to produce LDE in the thermodynamic limit and that the finite antiferromagnetic Heisenberg chain maximally entangles two spin-$1/2$ probes very far apart. These results support the current perspective of using quantum spin chains as entanglers or quantum channels in quantum information devices.

Current quantum computer technology is sufficient to realize weak measurements and the corresponding concept of “weak values.” We demonstrate how the weak value anomaly can be tested, along with consistency and simultaneity of weak values, using only discrete degrees of freedom. All that is needed is a quantum computer with two—or better, three—qubits. We also give an interpretation of the weak value as an effective field strength in a post-selected spin measurement.

We study a two-level atom in a double-well potential coupled to a continuum of electromagnetic modes (black-body radiation in three dimensions at zero absolute temperature). Internal and external degrees of freedom of the atom couple due to recoil during emission of a photon. We provide a full analysis of the problem in the long wavelengths limit up to the border of the Lamb-Dicke regime, including a study of the internal dynamics of the atom (spontaneous emission), the tunneling motion, and the electric field of the emitted photon. The tunneling process itself may or may not decohere depending on the wavelength corresponding to the internal transition compared to the distance between the two wells of the external potential, as well as on the spontaneous emission rate compared to the tunneling frequency. Interference fringes appear in the emitted light from a tunneling atom, or an atom in a stationary coherent superposition of its center-of-mass motion, if the wavelength is comparable to the well separation, but only if the external state of the atom is post selected.

The concept of $p$-orthogonality $(1⩽p⩽n)$ between $n$-particle states is introduced. It generalizes common orthogonality, which is equivalent to $n$-orthogonality, and strong orthogonality between fermionic states, which is equivalent to 1-orthogonality. Within the class of non-$p$-orthogonal states a finer measure of non-$p$-orthogonality is provided by Araki’s angles between $p$-internal spaces. The $p$-orthogonality concept is a geometric measure of indistinguishability that is independent of the representation chosen for the quantum states. It induces a hierarchy of approximations for group function methods. The simplifications that occur in the calculation of matrix elements among $p$-orthogonal group functions are presented.

Neutral atoms interact through a van der Waals potential which asymptotically falls off as $r^{-6}$. In ultracold gases, this interaction can be described to a good approximation by the atom-atom scattering length. However, corrections arise that depend on the characteristic length of the van der Waals potential. We parametrize these corrections by analyzing the energies of two- and few-atom systems under external harmonic confinement, obtained by numerically and analytically solving the Schrödinger equation. We generalize our results to particles interacting through a longer-ranged potential which asymptotically falls off as $r^{-4}$.

A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of $\mathrm{Cs}\left(6P_{1∕2}\right)$ atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium $6P_{1∕2}\left(F^{\prime }\right)\to 8S_{1∕2}\left(F^{″}\right)$ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the $6S_{1∕2}(F=4)\to 6P_{1∕2}$($F^{\prime }=3$ or 4) transition. Then, the frequency of a single mode cw dye laser is scanned over the $6P_{1∕2}\to 8S_{1∕2}$ manifold to probe the populations of the $6P_{1∕2}$ hyperfine levels. Absorption of probe laser photons is monitored by detecting $8S_{1∕2}\to 6P_{3∕2}$ fluorescence. The experiment is conducted at room temperature, where the Cs density is low $(n\sim 3.4\times {10}^{10}\mathrm{atoms}{\mathrm{cm}}^{-3})$, and thus the probability of a $\mathrm{Cs}\text{−}\mathrm{Cs}$ collision is negligible during the $\mathrm{Cs}\left(6P_{1∕2}\right)$ radiative lifetime. The Ar pressure is varied from 0 to $1.52\mathrm{Torr}$, and $\mathrm{Cs}\text{−}\mathrm{Ar}$ collisions cause population to be transferred from the directly excited $6P_{1∕2}\left(F^{\prime }\right)$ level to the other $6P_{1∕2}$ hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for $\mathrm{Cs}\left(6P_{1∕2}\right)\text{−}\mathrm{Ar}$ hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for $\mathrm{Cs}\left(6P_{1∕2}\right)$ atoms prepared with $v_z=0$ that undergo $F^{\prime }=3\leftrightarrow F^{\prime }=4$ hyperfine state-changing collisions with argon is reported.

We analyze numerically a rocking ratchet for cold atoms. The ratchet setup consists of a spatially symmetric dissipative optical lattice, and a biharmonic driving force. This setup corresponds to recent experimental realizations. We investigate the dependence of the features of the current generation on the scattering rate, which plays the role of the noise strength. Such a dependence is then used to investigate the origin of current reversals and of the rectification of fluctuations in a cold atom ratchet with broken Hamiltonian time symmetry.

The quantum and the classical multiphoton dissociation dynamics of diatomic Morse molecules driven by intense and ultrashort two-color laser pulses are investigated and compared. Special attention is given to the role of the relative phase of the monochromatic components of the pulses. We study the excitation of the system from the vibrational ground state and from excited states for several values of amplitude, frequency, and duration of the external pulses. Similar overall sensitivity of the dissociation threshold on the phase is observed in both quantum and classical approaches, provided the excitation frequency is sufficiently far from quantum resonances. In addition, we analyze the correspondence between the effects of the relative phase on the classical and quantum dynamics.

We investigate the problem of vortex trapping in cyclically coupled Bose-Josephson junctions. Starting with $N$ independent Bose-Einstein condensates we couple the condensates through Josephson links and allow the system to reach a stable circulation by adding a dissipative term in our semiclassical equations of motion. The central question we address concerns the probability of trapping a vortex with winding number $m$. Our numerical simulations reveal that the final distribution of winding numbers is narrower than the initial distribution of total phases, indicating an increased probability for no-vortex configurations. Specifically, the final width of the distribution of winding numbers for $N$ sites scales as $\lambda N^{\alpha }$, where $\alpha =0.47\pm 0.01$ and $\lambda <0.67$ (the value predicted for the initial distribution). The actual value of $\lambda$ is found to depend on the strength of dissipation. The nonlinearity of the problem also manifests itself in the result that it is possible to obtain a nonzero circulation starting with zero total phase around the loop.

We study the resonance fluorescence from a coherently driven four-level atom in the Y-type configuration. The effects of quantum interference induced by spontaneous emission on the fluorescence properties of the atom are investigated. It is found that the quantum interference resulting from cascade emission decays of the atom leads to a splitting of resonances in the excited-level populations calculated as a function of light detuning. For some parameters, interference-assisted enhancement of inner sidebands and narrowing of central peaks may also occur in the fluorescence spectrum. We present a physical understanding of our numerical results using the dressed-state description of the atom-light interaction.

Time delays for an intense transverse electric (TE) wave propagating through a Kerr-type nonlinear slab are investigated. The relation between the bidirectional group delay and the dwell time is derived and it is shown that the difference between them can be separated into three terms. The first one is the familiar self-interference time, due to the dispersion of the medium surrounding the slab. The other two terms are caused by the nonlinearity and oblique incidence of the TE wave. It is shown that the electric field distribution along the slab may be expressed in terms of Jacobi elliptic functions while the phase difference introduced by the slab is given in terms of incomplete elliptic integrals. The expressions for the field-intensity-dependent complex reflection and transmission coefficients are derived and the multivalued oscillatory behavior of the delay times for the case of a thin slab is demonstrated.

We propose a method that enables efficient frequency conversion of quantum information based on recently demonstrated strong parametric coupling between two single-photon pulses propagating in a slow-light atomic medium at different group velocities. We show that an incoming single-photon state is efficiently converted into another optical mode in a lossless and shape-conserving manner. The persistence of initial quantum coherence and entanglement within frequency conversion is also demonstrated. We first illustrate this result for the case of small frequency difference of converted photons, and then discuss the modified scheme for conversion of photon wavelengths in different spectral ranges. Finally we analyze the generation of a narrow-band single-photon frequency-entangled state.

We consider a meniscus between rotating and nonrotating species in the Bose-Einstein condensate with repulsive interatomic interactions, confined to a pipe-shaped trap. In this setting, we derive a system of coupled one-dimensional nonpolynomial Schrödinger equations for two mean-field wave functions. Using these equations, we analyze the phase separation and mixing in the pipe with periodic axial boundary conditions, i.e., in a toroidal configuration. We find that the onset of the mixing, in the form of suction, i.e., filling the empty core in the vortical component by its nonrotating counterpart, crucially depends on the vorticity of the first component and on the strengths of the interatomic interactions.