Based on numerical simulations, we show that higher-order nonlinear indices (up to $n_8$ and $n_{10}$, respectively) of air and argon have a dominant contribution to both focusing and defocusing in the self-guiding of ultrashort laser pulses over most of the spectrum. Plasma generation and filamentation are therefore decoupled. As a consequence, ultraviolet wavelength may not be the optimal wavelength for applications requiring to maximize ionization.

Amplified dispersive Fourier transformation (ADFT) is a powerful tool for fast real-time spectroscopy as it overcomes the limitations of traditional optical spectrometers. ADFT maps the spectrum of an optical pulse into a temporal waveform using group-velocity dispersion and simultaneously amplifies it in the optical domain. It greatly simplifies spectroscopy by replacing the diffraction grating and detector array in the conventional spectrometer with a dispersive fiber and single-pixel photodetector, enabling ultrafast real-time spectroscopic measurements. Following our earlier work on the theory of ADFT, here we study the effect of noise on ADFT. We derive the noise figure of ADFT and discuss its dependence on various parameters.

We study the possibility of performing quantum state tomography via equidistant states. This class of states allows us to propose a nonsymmetric informationally complete Positive Operator Valued Measure (POVM) based tomographic scheme. The scheme is defined for odd dimensions $N$ and involves the measurement of $N^2$ transition probabilities and an inversion, which can be analytically carried out by Fourier transform. The scheme can be modified to allow the reconstruction of states in the case of even dimensions at the expense of increasing the number of measurements to $3N^2/2$.

We study exact entanglement dynamics of three-qubit $W$-class states in a common structured cavity at zero temperature in both Markovian and non-Markovian regimes using the concept of lower bound of concurrence. We also propose three methods to control the qubits’ entanglement evolution and establish monogamy equalities relevant to the class of states under consideration.

Spectra and angular distributions of photoelectrons from ionization of atoms by a combination of two short pulses in the XUV and IR range are theoretically considered. The transition from the streaking regime for ultrashort XUV pulses to the sideband formation for longer pulses is discussed. For photoelectrons of sufficiently high energy (a few hundreds of eV), the peculiarity of the angular distribution and the gross structure of the sidebands are investigated.

Following photoexcitation of $\mathrm{Cl}\hspace{0.5em}2p$ electrons to various resonances, the dissociation dynamics of ionic and excited neutral fragments of gaseous ${\mathrm{CH}}_2{\mathrm{Cl}}_2$ was investigated by combined measurements of photon-induced ionic dissociation, x-ray absorption, and uv-visible dispersed fluorescence. The $\mathrm{Cl}\hspace{0.5em}2p$ core-to-Rydberg excitations near the ionization threshold produce a notable enhancement of excited neutral fragments (${\mathrm{C}}^{*}$ and ${\mathrm{CH}}^{*}$), which is attributed to the contribution from a shake-modified resonant Auger decay and postcollision interaction. The excitation $\mathrm{Cl}\hspace{0.5em}2p\hspace{0.5em}\to 10\hspace{0.5em}{a}_1^{*}$ induces an enhanced yield of ${{\mathrm{CH}}_2}^{+}$, possibly originating from fast dissociation via a strongly repulsive surface. The experimental results provide insight into the dissociation dynamics of ionic and excited neutral fragment production following core-level excitation.

A three-dimensional attractive Bose-Einstein condensate is expected to collapse when the number of the particles $N$ in the ground state or the interaction strength ${\lambda }_0$ exceeds a critical value. We study systems of different particle numbers and interaction strength and find that even if the overall ground state is collapsed there is a plethora of fragmented excited states that are still in the metastable region. Utilizing the configuration interaction expansion we determine the spectrum of the ground (“yrast”) and excited many-body states with definite total angular-momentum quantum numbers $0⩽L⩽N$ and $-L⩽M_L⩽L$, and we find and examine states that survive the collapse. This opens up the possibility of realizing a metastable system with overcritical numbers of bosons in a ground state with angular momentum $L\ne 0$. The multiorbital mean-field theory predictions about the existence of fragmented metastable states with overcritical numbers of bosons are verified and elucidated at the many-body level. The descriptions of the total angular momentum within the mean-field and the many-body approaches are compared.

Quantum nonlinear feedback control is developed for traveling optical fields. We first describe the discretization of the traveling optical fields. The discrete-time formulation is used to describe the stochastic master equation subject to homodyne measurement. Nonlinear feedback is formulated by directly feeding the measurement outcomes back to the traveling field through a multiplicative action. Since the measurement outcomes have a correlation with the system, the multiplicative feedback control can create nonlinear effects in the traveling field. In this formulation, a time delay is naturally introduced in the feedback loop. This is essentially different from instantaneous feedback in a continuous-time setting. As an example of the feedback scheme, a quantum nondemolition sum gate is considered. Numerical results show that quantum superposition state can be created by applying the feedback to a squeezed state.

We present experimental data on the coherent control of frequency conversion toward the vacuum-ultraviolet regime in xenon atoms, applying intense ultrashort picoseconds (ps) radiation pulses. We report on quantum interference between two resonantly enhanced frequency conversion processes (i.e., fifth harmonic generation and four-wave mixing). The conversion processes are driven by a fundamental (ps) laser pulse at 530 nm and the phase-locked second harmonic at 265 nm. Both fifth harmonic generation and four-wave mixing yield vacuum-ultraviolet radiation at 106 nm. The two frequency conversion pathways interfere with each other—either constructively or destructively, depending on the relative phase of the driving laser pulses. Thus, by variation of the relative phase, we substantially enhance or reduce the conversion efficiency (i.e., the yield of generated vacuum-ultraviolet radiation).

We propose a technique to characterize the dimensionality of entangled sources affected by any environment, including phase and amplitude masks or atmospheric turbulence. We illustrate this technique on the example of angular ghost diffraction using the orbital angular momentum (OAM) spectrum generated by a nonlocal double slit. We realize a nonlocal angular double slit by placing single angular slits in the paths of the signal and idler modes of the entangled light field generated by parametric down-conversion. Based on the observed OAM spectrum and the measured Shannon dimensionality spectrum of the possible quantum channels that contribute to Young’s ghost diffraction, we calculate the associated dimensionality $D_{\mathrm{total}}$. The measured $D_{\mathrm{total}}$ ranges between 1 and 2.74 depending on the opening angle of the angular slits. The ability to quantify the nature of high-dimensional entanglement is vital when considering quantum information protocols.

The second-order Talbot effect with thermal light is both theoretically and experimentally investigated. Three kinds of experimental schemes are performed, one of which reproduces the classical Talbot self-imaging and the others show plentiful self-imaging effects, in which an object with a periodic structure can be enlarged or diminished. The theoretical analysis, in good agreement with the experimental results, testifies that the specificity in the second-order Talbot effect refers to the joint diffraction of two correlated beams.

We introduce a ray model for coupled optical microdisks in which we select coupling-efficient rays among the splitting rays. We investigate the resulting phase-space structure and report island structures arising from the ray coupling between the two microdisks. We find the microdisks’s refractive index to influence the phase-space structure and calculate the stability and decay rates of the islands. Turning to ray-wave correspondence, we find many resonances to be directly related to the presence of these islands. We study the relation between the (ray-picture originating) island structures and the (wave-picture originating) spectral properties of resonances, especially the leakiness of the resonances represented as the imaginary part of the complex wave vector.

The full analytical solutions for plane terahertz waves generated through optical rectification in a slab of a nonlinear optical material are calculated. Terahertz dispersion, absorption of both optical and terahertz waves, and multiple reflections are considered. The results are valid for an arbitrary difference between the optical group index and the terahertz refractive index, including equal indices. It is demonstrated that the full terahertz wave is freely propagating and has no contribution of a “forced” pulse.

The influence of the strong laser-driven vacuum on a propagating electromagnetic probe wave has been studied in detail. We investigate two scenarios, which comprise a focused probe laser beam that passes through a region of vacuum polarized by an ultraintense laser field. By splitting this strong field into two separated monochromatic Gaussian pulses that counterpropagate in a plane perpendicular to the probe-field axis, we demonstrate a leading-order light-by-light diffraction effect that generates an interference pattern reminiscent of the classic double-slit experiment. We calculate the total number of probe photons diffracted as well as the number diffracted into regions where the vacuum polarization signal is higher than the probe background. In addition, we calculate the induced ellipticity and polarization rotation in the probe beam and show how, in the realistic situation in which the centers of the two strong fields are not exactly aligned, certain ranges of beam separation and observation distance may actually lead to an increase over the idealized case of a single strong laser beam.

The preparation of pseudopure states plays a central role in the implementation of quantum information processing in high-temperature ensemble systems, such as nuclear magnetic resonance. Here we describe a simple approach based on controlled-transfer gates which permits pseudopure states to be prepared efficiently using spatial averaging techniques.

The diode-laser-induced fluorescence spectra $b\hspace{0.5em}{}^3{\Pi }_{\Omega =0}^{+}\to X^{\hspace{0.5em}1}{\Sigma }^{+}$ originated from the rovibronic levels of the “dark” triplet $b\hspace{0.5em}{}^3{\Pi }_{\Omega =0}^{+}$ state of KCs dimers were recorded with a Fourier transform spectrometer with a resolution of 0.03 cm${}^{-1}$. Term values of 30 rovibronic levels $(v_{b0}^{*}\in [14,18];J^{\prime }\in [47,134])$ below the minimum of perturbing $A\hspace{0.5em}{}^1{\Sigma }^{+}$ state were determined with 0.003–0.01 cm${}^{-1}$ uncertainty. The optimal excitation and detection lines for very weak spin-forbidden $b\hspace{0.5em}{}^3{\Pi }_{\Omega =0}^{+}-X^{\hspace{0.5em}1}{\Sigma }^{+}$ transitions have been properly predicted in the framework of the coupled-channels deperturbation analysis recently performed for the singlet-triplet $A\hspace{0.5em}{}^1{\Sigma }^{+}-b\hspace{0.5em}{}^3{\Pi }_{\Omega =0,1,2}^{+}$ complex [A. Kruzins et al., Phys. Rev. A 81, 042509 (2010)]. The lowest observed triplet level has only 8.6$\%$ of singlet admixture.

Binding energies of the fine-structure levels of the indium negative ion In${}^{-}$ are measured using infrared photodetachment threshold spectroscopy. The relative cross section for neutral atom production is measured with a crossed ion-beam–laser-beam apparatus over selected photon energy ranges between 300 and 700 meV. An $s$-wave threshold is observed due to the opening of the In${}^{-}$ ($5p^2$${}^3{P}_0$) to In($5p$${}^2{P}_{1/2}$) ground-state-to-ground-state transition, which determines the electron affinity of In to be 383.92(6) meV. The present result is in good agreement with previous theoretical calculations, but it differs substantially from the previously measured electron affinity and reduces the uncertainty by a factor of 150. $s$-wave thresholds are also observed for detachment from the excited fine-structure levels of In${}^{-}$, permitting accurate determination of the fine-structure intervals of 76.06(7) meV for $J=0–1$ and 170.6(6) meV for $J=0–2$, which are in good agreement with the previous measurements and substantially reduce the uncertainties.

Considering the photoionization of the $\mathrm{Xe}@{\mathrm{C}}_{60}$ endohedral compound, we study in detail the ionization cross sections of various levels of the system at energies higher than the plasmon resonance region. Five classes of single-electron levels are identified depending on their spectral character. Each class engenders distinct oscillations in the cross section, emerging from the interference between active ionization modes specific to that class. Analysis of the cross sections based on their Fourier transforms unravels oscillation frequencies that carry unique fingerprints of the emitting level.

Translationally cold and slow ND${}_3$ is prepared by filtering the slow molecules from a thermal gas-phase sample using a curved electrostatic hexapole guide. This filter, like the curved quadrupole guide introduced by Rangwala et al. [Phys. Rev. A 67, 043406 (2003)] selects molecules by their forward velocity and effective electric dipole moment. Here we describe two main modifications with respect to previous work: (1) A segmented hexapole guide is used that produces a harmonic potential for the linearly Stark-shifted levels of ND${}_3$. A curved guide is combined with a straight hexapole guide, and independent high-voltage supplies are employed to allow for bandpass velocity filtering. (2) State-selective laser ionization is used to obtain time- and state-selective detection of the guided molecules. This enables the experimental determination of the rotational state population of the guided molecules.

We consider basic dynamical effects in settings based on a pair of local potential traps that may be effectively switched on and off, or suddenly displaced, by means of appropriate control mechanisms, such as scanning tunneling microscopy or photo-switchable quantum dots. The same models, based on the linear Schrödinger equation with time-dependent trapping potentials, apply to the description of optical planar systems designed for the switching of trapped light beams. The analysis is carried out in the analytical form, using exact solutions of the Schrödinger equation. The first dynamical problem considered in this work is the retention of a particle released from a trap which was suddenly turned off, while another local trap was switched on at a distance—immediately or with a delay. In this case, we demonstrate that the maximum of the retention rate is achieved at a specific finite value of the strength of the new trap, and at a finite value of the temporal delay, depending on the distance between the two traps. Another problem is retrapping of the bound particle when the addition of the second trap transforms the single-well setting into a double-well potential (DWP). In that case, we find probabilities for the retrapping into the ground or first excited state of the DWP. We also analyze effects entailed by the application of a kick to a bound particle, the most interesting one being a kick-induced transition between the DWP’s ground and excited states. In the latter case, the largest transition probability is achieved at a particular strength of the kick.