We present various differential cross sections for the single ionization of Li by O${}^{8+}$ ions. We use a time-dependent, close-coupling approach to model the evolution of a one-active-electron wave function in the field of the incoming projectile for a range of impact parameters. In addition, a Fourier transform approach is used to extract differential cross sections for a specific projectile momentum transfer value. This scheme allows us to incorporate information about the interaction of the two heavy nuclei [the so-called nuclear-nuclear (NN) interaction] and to assess its influence in the differential cross sections. We find noticeable differences in the shape of the differential cross sections when we include (neglect) the NN interaction. Our single-differential cross-section calculation shows excellent agreement with experimental data. In addition, recent measured double-differential cross sections as a function of electron energy and transverse momentum transfer are reasonably well reproduced by our theoretical calculations.

We characterize a synchrotron for polar molecules that consists of forty straight hexapoles arranged in a circle. By modulating either the voltages or the duration of the high-voltage pulses that are applied to the hexapoles, we shake the transverse and longitudinal well. If the frequency of the modulation matches a characteristic frequency of a stored molecule, the amplitude of the motion is resonantly excited, leading to a decrease in the number of molecules that are stored. From this, we determine the longitudinal, vertical, and radial frequencies that characterize the motion of the molecules inside the synchrotron and obtain knowledge about the couplings between the longitidinal and transverse motion. The measured frequencies are in good agreement with those obtained from three-dimensional trajectory calculations.

The weak-field asymptotic theory (WFAT) of tunneling ionization in a static electric field is developed to the next order in field. The first-order corrections to the ionization rate and transverse momentum distribution of the ionized electrons are derived. This extends the region of applicability of the WFAT at the quantitative level toward stronger fields, practically up to the boundary between tunneling and over-the-barrier regimes of ionization. The results apply to any atom or molecule treated in the single-active-electron and frozen-nuclei approximations. The theory is illustrated by calculations for hydrogen and noble-gas atoms.

We have developed a combined Stark-velocity-filter–ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND${}_3$, H${}_2$CO, and CH${}_3$CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND${}_3$, H${}_2$CO, and CH${}_3$CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of $n={10}^4$ to 10${}^6$ cm${}^{-3}$ by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca${}^{+}$ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10${}^{-5}$ s${}^{-1}$, which are much slower than typical reaction rates of molecular ion–polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca${}^{+}$ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N${}_2$H${}^{+}$ ions and velocity-selected CH${}_3$CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)$\times$10${}^{-3}$ s${}^{-1}$ is much faster than those of the Ca${}^{+}$+PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH${}_3$CN+N${}_2$H${}^{+}$ $\to$ CH${}_3$CNH${}^{+}$+N${}_2$ is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su et al. In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion–polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.

We investigate finite-number effects in collisions between two states of an initially well-known number of identical bosons with contact interactions, oscillating in the presence of harmonic confinement in one dimension. We investigate two $N/2$ (interacting) ground states, which are initially displaced from the trap center, and the effects of varying interaction strength. The numerics focus on the simplest case of $N=4$. In the noninteracting case, such a system would display periodic oscillation with a half harmonic oscillator period (due to the left-right symmetry). With the addition of contact interactions between the bosons, collisions generate entanglement between each of the states and distribute energy into other modes of the oscillator. We study the system numerically via an exact diagonalization of the Hamiltonian with a finite basis, investigating left-right number uncertainty as our primary measure of entanglement. Additionally, we study the time evolution and equilibration of the single-body von Neumann entropy for both the attractive and repulsive cases. We identify parameter regimes for which attractive interactions create behavior qualitatively different from that of repulsive interactions, due to the presence of bound states (quantum solitons), and explain the processes behind this.

The well-known $\Lambda$ system using two ground-state hyperfine levels, $F_g=1$ and $F_g=2$ of $5S_{1/2}$, and one hyperfine level, $F_e=2$ of excited state of $5P_{3/2}$ of ${}^{87}$Rb, has been recently studied using two counterpropagating control lasers [Sapam Ranjita Chanu, Kanhaiya Pandey, and Vasant Natarajan, Europhys. Lett. 98, 44009 (2012)]. The experiment shows conversion of electromagnetically induced transparency into electromagnetically induced absorption because the doubly driven $\Lambda$ system forms various subsystems. We here present a detailed theoretical study of the different possible subsystems created by this configuration. We also explore the possibility of tuning the strength of individual subsystems by changing the polarization of the control lasers.

Using the collective variable approach technique, we analyze propagation of elliptical Gaussian beams in nonlinear waveguides with a parabolic graded-index (GRIN) profile. We considered both saturable and cubic-quintic models to describe the nonlinearity, taking into account both linear and nonlinear absorption. For lossless media, we construct diagrams, which define regions of self-focusing and self-diffractive beam propagation for both models in GRIN waveguides and compare them with those for nongraded waveguides. The widths of the propagating elliptic beam exhibit an oscillatory pattern, similar to the “breathing” and “beating” behavior found in nongraded media. Two types of beating oscillations are observed in both models. We calculate the dependence of $L_{\mathrm{beat}}/L_{\mathrm{br}}$, the ratio of the “beating” to “breathing” oscillation periods, on the beam ellipticity $\rho$ and the GRIN index $g$. We find that there is a remarkable difference in this dependence between saturable and cubic-quintic media: in the saturable model, $L_{\mathrm{beat}}/L_{\mathrm{br}}$ is a monotonic function of $\rho$, whereas in the cubic-quintic model, it is characterized by singularities, which correspond to transitions between the types of beat oscillations. For lossy media, we discuss the difference between the breathing behavior in nongraded and GRIN waveguides.

We consider a driven single-mode Dicke-Hamiltonian coupled to a dissipative zero-temperature bath. We derive the cumulant generating function for emitted photons of this quantum-critical system by using a $P$ representation of the master equation in the thermodynamic limit. This cumulant generating function is shown to consist of two parts: a macroscopic component, which is Poissonian in nature with characteristic rate proportional to the order parameter of the system, and a part describing fluctuations, which is nontrivial in form and divergent around the quantum phase transition.

We theoretically study a method for all-optical delay of images based on backward four-wave mixing in composites containing metal nanoparticles. In this approach a delayed phase-conjugate probe pulse is generated by the interaction of two counterpropagating pump beams and a noncollinear shaped probe pulse in the nanocomposite. The fractional delay and the reflectivity for the phase-conjugate signal pulses are studied as functions of the input pump intensity. It is shown that this scheme can be used for delayed imaging combined with the elimination of optical diffraction. The advantages of this method include miniaturized design, tunable wavelength range up to the telecommunication range, and wide bandwidth.

We present a theoretical framework to tackle quantum non-Markovian dynamics based on a microscopic collision model (CM), where the bath consists of a large collection of initially uncorrelated ancillas. Unlike standard memoryless CMs, we endow the bath with memory by introducing interancillary collisions between next system-ancilla interactions. Our model interpolates between a fully Markovian dynamics and the continuous interaction of the system with a single ancilla, i.e., a strongly non-Markovian process. We show that in the continuous limit one can derive a general master equation, which, while keeping such features, is guaranteed to describe an unconditionally completely positive and trace-preserving dynamics. We apply our theory to an atom in a dissipative cavity for a Lorentzian spectral density of bath modes, a dynamics which can be exactly solved. The predicted evolution shows a significant improvement in approaching the exact solution with respect to two well-known memory-kernel master equations.

Bases of exactly localized Minkowski and Rindler states on spacelike hypersurfaces are used to describe inertial and accelerated photon counting devices. It is found that the space-time coordinates of photons absorbed by a pair of counteraccelerating detectors in causally disconnected Rindler wedges are correlated. If a photon is absorbed by a single accelerated detector, the Minkowski vacuum collapses to a state containing at least one photon and that photon can be absorbed by an inertial detector.

We developed a non-Hermitian quantum optimization algorithm to find the ground state of the ferromagnetic Ising model with up to 1024 spins (qubits). Our approach leads to significant reduction of the annealing time. Analytical and numerical results demonstrate that the total annealing time is proportional to $\ln N$, where $N$ is the number of spins. This encouraging result is important in using classical computers in combination with quantum algorithms for the fast solutions of NP-complete problems. Additional research is proposed for extending our dissipative algorithm to more complicated problems.

Bound states of dipole-bound anions are studied by using a nonadiabatic pseudopotential method and the Berggren expansion involving bound states, decaying resonant states, and nonresonant scattering continuum. The method is benchmarked by using the traditional technique of direct integration of coupled-channel equations. A good agreement between the two methods has been found for well-bound states. For weakly bound subthreshold states with binding energies comparable to rotational energies of the anion, the direct integration approach breaks down and the Berggren expansion method becomes the tool of choice.

The $N$-quantum approach (NQA) to quantum field theory uses the complete and irreducible set of $\mathit{in}$ or out fields, including $\mathit{in}$ or out fields for bound states, as standard building blocks to construct solutions to quantum field theories. In particular, introducing $\mathit{in}$ (or out) fields for the bound states allows an alternative way of calculating energy levels and wave functions for the bound states that is both covariant and effectively three dimensional. This method is independent of the Bethe-Salpeter equation. In contrast to the Bethe-Salpeter equation, all solutions of the NQA are normalizable and correspond to physical bound states. In this paper we use the NQA in one-loop approximation to calculate states of the relativistic hydrogen atom and analogous two-body systems to illustrate how our method works. With additional terms in the $\mathit{in}$ field expansion we find systematic corrections beyond the Coulomb interaction.

In previous papers [Bhatia, Phys. Rev. A 85, 052708 (2012); Bhatia, Phys. Rev. A 86, 032709 (2012)] electron-hydrogen and electron-He${}^{+}$ $P$-wave scattering phase shifts were calculated using the hybrid theory. This method is extended to the singlet and triplet electron-Li${}^{2+}$ $P$-wave scattering in the elastic region, where the correlation functions are of Hylleraas type. The short-range and long-range correlations are included in the Schrödinger equation at the same time, by using a combination of a modified method of polarized orbitals and the optical potential formalism. Phase shifts are compared to those obtained by other methods. The present calculation requires very few correlation functions to obtain accurate results which are rigorous lower bounds to the exact phase shifts. The continuum functions obtained in this method are used to calculate photodetachment and photoionization cross sections of two-electron systems H${}^{-}$, He, and Li${}^{+}$. Cross sections of the metastable ${}^{1,3}S$ states of He, and Li${}^{+}$ are also calculated. These cross sections are calculated in the elastic region and compared with previous calculations. Using these cross sections, the Maxwellian-averaged radiative-recombination rates at various electron temperatures are also calculated.

We investigate the dynamics of two interacting bosons repeatedly scattering off a beam-splitter in a free oscillation atom interferometer. Using the interparticle scattering length and the beam-splitter probabilites as our control parameters, we show that even in a simple setup like this a wide range of strongly correlated quantum states can be created. This in particular includes the NOON state, which maximizes the quantum Fisher information and is a foremost state in quantum metrology.

We investigate the creation of stable homonuclear and heteronuclear $N$-body polymer molecules from ultracold atoms via a generalized stimulated Raman adiabatic passage scheme. The atom-molecule dark-state solutions for the system are obtained and are found to satisfy universal algebraic equations. We discuss the linear instability and the adiabatic fidelity of the dark state. We also explore the effects of the interparticle interactions, the atomic number of the polymer, and external field parameters on the conversion process.

We show that, in two-path optical interferometry, the measurement of photon number parity achieves maximal phase sensitivity at the quantum Cramér-Rao bound for a certain type of path-symmetric states. All pure states of light proposed for sub–shot-noise phase sensitivity thus far in the literature are of the form of these path-symmetric states. Thus, parity measurement presents an optimal detection strategy for all of them. Our scheme is applicable for local phase estimation.

An experimental study of bound states of two solitons and of three solitons in dispersion-managed fibers is presented. The existence regime and stability of such soliton molecules is investigated. With a programmable pulse shaper we can flexibly shape launch signals; received signals are detected in amplitude and phase, and in relative position and velocity. An equilibrium separation is demonstrated for both two-soliton and three-soliton soliton molecules. It is also shown that stable molecules are possible only with antiphase pulses. Both types of soliton molecule are viable for transmission in the same fiber, at the same wavelength. Together with single solitons this opens the possibility of quaternary data transmission in a soliton-based format.

Spectrographs take snapshots of photon spectra with array detectors by dispersing photons of different energies into distinct directions and spatial locations. Spectrographs require optics with a large angular dispersion rate as the key component. In visible light optics, diffraction gratings are used for this purpose. In the hard-x-ray regime, achieving large dispersion rates is a challenge. Here we show that multicrystal, multi-Bragg-reflection arrangements feature cumulative angular dispersion rates almost two orders of magnitude larger than those attainable with a single-Bragg reflection. As a result, the multicrystal arrangements become potential dispersing elements of hard-x-ray spectrographs. The hard-x-ray spectrograph principles are demonstrated by imaging a spectrum of photons with a record high resolution of $\Delta E\simeq 90$ $\mu$eV in the hard-x-ray regime, using multicrystal optics as the dispersing element. The spectrographs can boost research using inelastic ultrahigh-resolution x-ray spectroscopies with synchrotrons and seeded x-ray free electron lasers.