Correlated imaging through atmospheric turbulence is studied, and the analytical expressions describing turbulence effects on image resolution are derived. Compared with direct imaging, correlated imaging can reduce the influence of turbulence to a certain extent and reconstruct high-resolution images. The result is backed up by numerical simulations, in which turbulence-induced phase perturbations are simulated by random-phase screens inserted into propagation paths.

The photon statistics of atomic fluorescence after $\pi$-pulse excitation is investigated in a system in which the input and output ports are connected to an atom. Since spontaneous decay during input pulse excitation occurs, the output pulse generally contains a multiphoton component with a certain probability. We quantitatively evaluate the probability of the output pulse containing multiple photons and determine the conditions for ideal single-photon generation.

Motivated by recent experiments, we study four-wave-mixing in an atomic double-$\Lambda$ system driven by a far-detuned pump. Using the Heisenberg-Langevin formalism, and based on the microscopic properties of the medium, we calculate the classical and quantum properties of seed and conjugate beams beyond the linear amplifier approximation. A continuous-variable approach gives us access to relative-intensity noise spectra that can be directly compared with experiments. Restricting ourselves to the cold-atom regime, we predict the generation of quantum-correlated beams with a relative-intensity noise spectrum well below the standard quantum limit (down to $-6$ dB). Moreover, entanglement between seed and conjugate beams measured by an inseparability down to $0.25$ is expected. This work opens the way to the generation of entangled beams by four-wave mixing in a cold-atom sample.

Graphical rule, describing that any single-mode homodyne detection turns a given continuous-variable (CV) graph state into a new one, is presented. Employing two simple graphical rules—local complement operation and vertex deletion (single quadrature-amplitude $\mathrm{x̂}$ measurement)—the graphical rule for any single-mode quadrature component measurement can be obtained. The shape of CV weighted graph state may be designed and constructed easily from a given larger graph state by applying this graphical rule.

Aluminum cluster anions were stored in an electrostatic ion storage ring and irradiated by a laser pulse. Neutral as well as charged decay products emitted $20\hspace{0.5em}\mathrm{\mu }\mathrm{s}$ after the excitation were identified and recorded using the daughter ion mass spectrometry method. Besides delayed electron detachment, only monomer emission was observed for ${{\mathrm{Al}}_4}^{-}$. The branching ratio for the monomer channel was determined to be $8\pm 2\%$, while the dimer channel was found to be $<0.01\%$.

We consider the situation where $s$ replicas of a qubit with an unknown state and its orthogonal $k$ replicas are given as an input, and we try to make $c$ clones of the qubit with the unknown state. As a function of $s$, $k$, and $c$, we obtain the optimal fidelity between the qubit with an unknown state and the clone by explicitly giving a completely positive trace-preserving (CPTP) map that represents a cloning machine. We discuss dependency of the fidelity on the values of the parameters $s$, $k$, and $c$.

The emission of x-ray satellite lines in the $K\alpha$ region of Mg, Si, Sc, Ti, Cr, Fe, Ni, and Zn induced by electron incidence was studied by means of wavelength dispersive spectroscopy. The satellite lines studied were $K{\alpha }^{\prime }$, $K{\alpha }_3$, $K{\alpha }_4$, $K{\alpha }_5$, $K{\alpha }_6$, and two transitions denoted here as $K{\alpha }_{22}$ and $K{\alpha }_{12}$. Energy shifts with respect to the main $K{\alpha }_1$ diagram line and transition probabilities relative to the whole $K\alpha$ group were determined for a number of lines through a careful spectral processing. The dependence of these parameters, as well as of the $K\beta :K\alpha$ intensity ratio, on the atomic number was compared with previous experimental and theoretical determinations when available. A discussion about the different mechanisms responsible for vacancy creation involved in the production of double-ionization satellites was performed in the light of the results obtained. Finally, the behavior of the satellite intensities as a function of the incidence energy was discussed for silicon.

The theory of resonance charge exchange in slow collisions of a proton with a hydrogen atom in the excited state is developed. It extends the Firsov-Demkov theory of resonance charge exchange to the case of degenerate initial and final states. The theory is illustrated by semiclassical and quantum calculations of charge exchange cross sections between states with $n=2$ in parabolic and spherical coordinates. The results are compared with existing close-coupling calculations.

A dynamic process of repeating collisions of a pair of trapped neutral particles with weak spin-dependent interaction is designed and studied. A related theoretical derivation and numerical calculation have been performed to study the inherent coordinate-spin and momentum-spin correlations. Because of the repeating collisions, the effect of the weak interaction can be accumulated and enlarged, and therefore can be eventually detected. Numerical results suggest that the Cr-Cr interaction, which has not yet been completely clarified, could thereby be determined. The design can be used in general to determine various interactions among neutral atoms and molecules, in particular for the determination of very weak forces.

We report the preparation and observation of translationally cold atoms using kinematic cooling. In these experiments, krypton atoms are cooled to subkelvin temperatures by elastic collisions in crossed atomic beams. Two independent velocity measurements indicate an upper-bound mean velocity of 13 m/s ($E_{\mathrm{trans}}/k=850\hspace{0.5em}\mathrm{mK}$) and are consistent with a much lower mean velocity of 4 m/s ($E_{\mathrm{trans}}/k=80\hspace{0.5em}\mathrm{mK}$) ($k$ is Boltzmann’s constant). The density of the cold atoms is measured to be ${10}^9$ atoms/cm${}^3$. Scattering calculations and diffusion models support these velocity and density measurements. The results demonstrate that cold, dense samples of ground-state atoms and molecules can be prepared by elastic collisions between identical collision partners.

Single-photon cooling (SPC), noted for its potential as a versatile method for cooling a variety of atomic species, has recently been demonstrated experimentally. In this paper, we study possible ways to improve the performance of SPC by applying it to atoms trapped inside a wedge billiard. The main feature of the wedge billiard for atoms, also experimentally realized recently, is that the nature of atomic trajectories within it changes from stable periodic orbit to random chaotic motion with the change in wedge angle. We find that a high cooling efficiency is possible in this system with a relatively weak dependence on the wedge angle and that chaotic dynamics, rather than a regular orbit, is more desirable for enhancing the performance of SPC.

In this article, we address two strong-field phenomena which attract much attention and can be observed under similar experimental conditions, namely when a gas is ionized by ultrashort laser pulses. The first phenomenon is the excitation of high-order harmonics of the driving field frequency in the electron current, which leads to the generation of extreme UV and soft-x-ray radiation. The second phenomenon is the excitation of a quasi-dc residual current in the laser-produced plasma, which results in the generation of radiation having a frequency below the laser one, e.g., THz waves. We present alternative one- and two-dimensional quantum-mechanical models for the description of such phenomena for the gas consisting of H atoms and the generalization of these models to the various noble gases. The shape of the electrostatic potential produced by an atomic ion is shown to influence significantly the rates of the processes in the dynamics of atomic electron and, even more, the rate of tunneling ionization, which is of utmost importance for the considered phenomena. The results of solving the time-dependent Schrödinger equation with the proposed model potentials are compared with the results of the ab initio three-dimensional calculations for the H atom. We find that in a wide range of laser pulse parameters the results obtained with proposed models have much better accuracy than the results provided by the models used earlier.

The effect of incident light field ellipticity on the electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) resonances has been studied experimentally and computationally in Hanle configuration with longitudinal and transverse magnetic fields. We identify the Zeeman coherences that influence the resonance profile and study the role of coherence-transfer from excited to ground state via spontaneous emission as a function of ellipticity for the $F_g=2\to F_e=3$ transition of ${}^{87}\mathrm{Rb}$. The EIT resonance observed with the light field locked on the $F_g=1\to F_e=2$ transition of ${}^{87}\mathrm{Rb}$ is an influence of the nearby $F_g=1\to F_e=0$ closed and $F_g=1\to F_e=1$ open transitions. With increase in ellipticity the observed EIA and EIT resonances diminish in amplitude for a longitudinal magnetic field and are enhanced for a transverse magnetic field. We computationally account for these observations and discuss the factors that influence the EIA and EIT resonance amplitudes as a function of ellipticity and show that for a transverse field scan the ellipticity dependence of the EIA resonance amplitude can be accounted for without invoking the Doppler effect unlike for a longitudinal field scan. We also show that the maximum in the EIA resonance amplitude obtained for nonzero ellipticities with a longitudinal magnetic field depends on the closedness of the atomic system.

We propose a model for a continuously pumped single-pass amplifier for continuous and pulsed laser beams. The model takes into account Gaussian shape and focusing geometry of pump and seed beam. As the full-wave simulation is complex we have developed a largely simplified numerical method that can be applied to rotationally symmetric geometries. With the tapered-shell model we treat (focused) propagation and amplification of an initially Gaussian beam in a gain crystal. The implementation can be done with a few lines of code that are given in this paper. With this code, a numerical parameter optimization is straightforward and example results are shown. We compare the results of our simple model with those of a full-wave simulation and show that they agree well. A comparison of model and experimental data also shows good agreement. We investigate in detail different regimes of amplification, namely the unsaturated, the fully saturated, and the intermediate regime. Because the amplification process is affected by spatially varying saturation and exhibits a nonlinear response against pump and seed power, no analytical expression for the expected output is available. For modeling of the amplification we employ a four-level system and show that if the fluorescence lifetime of the gain medium is larger than the inverse repetition rate of the seed beam, continuous-wave amplification can be employed to describe the amplification process of ultrashort pulse trains. We limit ourselves to this regime, which implies that if titanium:sapphire is chosen as gain medium the laser repetition rate has to be larger than a few megahertz. We show detailed simulation results for titanium:sapphire for a large parameter set.

A theoretical description for nonlinear beam propagation in a two-dimensional optical lattice in the presence of a refractive-index gradient has been developed. This problem is associated with nonlinear Bloch oscillations; it has been reduced to a nonlinear Schrödinger equation with a varying dispersion coefficient. It is shown that, if the periodicity of longitudinal modulation coincides with the transverse gradient of the refractive index, a stationary oscillatory picture emerges in the nonlinear regime.

We briefly report on zero-temperature photoassociation of a Bose-Einstein condensate, focusing on the many-body rate limit for atom-molecule conversion. An upgraded model that explicitly includes spontaneous radiative decay leads to an unanticipated shift in the position of the photoassociation resonance, which affects whether the rate (constant) maximizes or saturates, as well as the limiting value itself. A simple analytical model agrees with numerical experiments, but only for high density. Finally, an explicit comparison with the two-body unitary limit, set by the size of the condensate, finds that the many-body rate limit is generally more strict.

We study the equilibration behavior following local quenches, using frustrated quantum spin chains as an example of interacting closed quantum systems. Specifically, we examine the statistics of the time series of the Loschmidt echo, the trace distance of the time-evolved local density matrix to its average state, and the local magnetization. Depending on the quench parameters, the equilibration statistics of these quantities show features of good or poor equilibration, indicated by Gaussian, exponential, or bistable distribution functions. These universal functions provide valuable tools to characterize the various time-evolution responses and give insight into the plethora of equilibration phenomena in complex quantum systems.

The SO radical with an even number of electrons belongs to an open-shell system due to its ${\pi }^2$ ground-state electronic configuration. This configuration gives rise to three low-lying states $X\hspace{0.5em}{}^3{\Sigma }^{-}$, $a\hspace{0.5em}{}^1\Delta$, and $b\hspace{0.5em}{}^1{\Sigma }^{+}$. The inclusion of these target states in a trial wave function of the entire scattering have important implications in the resonances that may be detected in this open-shell molecule. The $R$-matrix method is a well-established ab initio formalism which is employed to calculate elastic differential and integral cross sections, momentum-transfer cross sections, and inelastic cross sections. The Hartree-Fock ground-state configuration of SO is $1{\sigma }^{2}2{\sigma }^{2}3{\sigma }^{2}4{\sigma }^{2}1{\pi }^{4}5{\sigma }^{2}6{\sigma }^{2}7{\sigma }^{2}2{\pi }^{4}3{\pi }^2$. We have included 28 target states in the trial wave function of the scattering system. In our configuration-interaction (CI) model, we freeze $12$ electrons in orbitals $1\sigma$, $2\sigma$, $3\sigma$, $4\sigma$, and $1\pi$, the remaining 12 electrons are free to move among the eight orbitals $4\sigma$, $5\sigma$, $6\sigma$, $7\sigma$, $8\sigma$, $9\sigma$, $2\pi$, and $3\pi$. We have carried our scattering calculations in static-exchange, one-state with CI wave function, and 28-state models. We have detected a stable anionic bound state ${}^2{B}_1$ of SO at various bond lengths of SO molecule. The vertical electron affinity value is 0.970 eV, which is comparable to the experimental value of 1.125 eV. We also detected two core-excited shape resonances, both of ${}^2\Pi$ symmetry and with ${}^1\Delta$ and ${}^1{\Sigma }^{+}$ as the parent states.

We have measured the ejected electron signals from Ba $6p_{1/2}\mathit{nk}$ autoionizing Stark states, of $n=28$ and 29, produced by linearly polarized laser excitation in weak electric fields. These states do not have well-defined parities and as a result do not lead to angular distributions which are up-down symmetric with respect to the laser polarization direction. The weakness of the electric field makes the observation of the up-down asymmetry of the ejected electrons possible. We observe that the electrons from Ba $6p_{1/2}\mathit{nk}$ autoionizing red states are ejected in the upfield direction, while the electron from Ba $6p_{1/2}\mathit{nk}$ autoionizing blue states are ejected in the downfield direction.

We propose a general and scalable approach to isotope separation. The method is based on an irreversible change of the mass-to-magnetic moment ratio of a particular isotope in an atomic beam, followed by a magnetic multipole whose gradients deflect and guide the atoms. The underlying mechanism is a reduction of the entropy of the beam by the information of a single scattered photon for each atom that is separated. We numerically simulate isotope separation for a range of examples, which demonstrate this technique’s general applicability to almost the entire periodic table. The practical importance of the proposed method is that large-scale isotope separation should be possible, using ordinary inexpensive magnets and the existing technologies of supersonic beams and lasers.