We have measured the total electron detachment cross sections of the negative ions C${}^{-}$, CH${}^{-}$, C${}_2^{-}$, and C${}_2$H${}^{-}$ incident on molecular nitrogen in the velocity range 0.22–0.56 a.u. The data were measured with reliable normalization and, particularly in the critical case of the C${}^{-}$ projectile, the absence of beam contamination due to long-lived metastable states. Comparison of all measurements of cross sections with experimental data for other projectiles shows a common velocity dependence with a maximum near 0.4 a.u. This behavior suggests a connection between the anion-N${}_2$ electron-loss collision dynamics and that of the shape-resonance process dominant in low-velocity electron-N${}_2$ total electron scattering.

A manipulatable half-cycle-like field (HCLF), homochromy with the driving femtosecond laser, is applied to enhance the harmonic emission by optimizing their relative delay time. We find that, by numerical computation, the HCLF can deliver a substantial momentum to the accelerated electrons as they return to their parent ions by a suitable phase delay, and also significantly increase the atomic ionization rate supplementarily. The results show that the harmonic order of the maximum or cut-off photon energy emitted in the presence of a half-cycle manipulating light pulse is risen to the 177th order, which is a significant increase compared with the 53rd order harmonics in the case of a single driving light pulse. To understand the essence from the wave-packet kinetics of the return electrons and their relation to the harmonic emission, we utilize the phase-space analysis of the coordinate momentum of an electronic wave packet by using a Gabor transformation, by which the presented numerical conclusions are further confirmed.

We measure the ac Stark shifts of the $5S_{1/2},F=2\to 5P_{3/2},F^{\prime }=3$ transitions of individual optically trapped ${}^{87}$Rb atoms using a nondestructive detection technique that allows us to measure the fluorescent signal of one and the same atom for over 60 s. These measurements allow the efficient and rapid characterization of single-atom traps that is required for many coherent quantum information protocols. Although this method is demonstrated using a single-atom trap, the concept is readily extended to resolvable atomic arrays.

We employ semiclassical theoretical analysis to study laser cooling of free atoms using three-level cascade transitions, where the upper transition is much weaker than the lower one. This represents an alternate cooling scheme, particularly useful for group II atoms. We find that temperatures below the Doppler limits associated with each of these transitions are expected. The lowest temperatures arise from a remarkable increase in damping and reduced diffusion compared to two-level cooling. They are reached at the two-photon resonance, where there is a crossing between the narrow and the partially dark dressed states, and can be estimated simply by the usual Doppler limit considering the decay rate of the optical coherence between these states.

We demonstrate that quantum coherence can be generated by the interplay of coupling to an incoherent environment and kinetic processes. This joint effect even occurs in a repulsively interacting fermionic system initially prepared in an incoherent Mott insulating state. In this case, coupling a dissipative noise field to the local spin density produces coherent pairs of fermions. The generated pair coherence, while metastable, is long lived and spatially extended. This conceptually surprising approach provides a path towards a better control of quantum many-body correlations.

The properties of two-component Fermi gases become universal if the interspecies $s$-wave scattering length $a_s$ and the average interparticle spacing are much larger than the range of the underlying two-body potential. Using an explicitly correlated Gaussian basis set expansion approach, we determine the eigenenergies of two-component Fermi gases in a cubic box with periodic boundary conditions as functions of the interspecies $s$-wave scattering length and the effective range of the two-body potential. The universal properties of systems consisting of up to four particles are determined by extrapolating the finite-range energies to the zero-range limit. We determine the eigenenergies of states with vanishing and finite momenta. In the weakly attractive BCS regime, we analyze the energy spectra and degeneracies using first-order degenerate perturbation theory. Excellent agreement between the perturbative energy shifts and the numerically determined energies is obtained. For the infinitely large scattering length case, we compare our results—where available—with those presented in the literature.

Based on the generalized Lorenz-Mie theory and Maxwell stress tensor formulism, we calculate the transverse force constant matrix and perform a linear stability analysis on a spherical particle that is subject to negative longitudinal optical force (NLOF) under the illumination of Bessel beams. Phase diagrams with respect to the material parameters are presented, which exhibit the possibility of the appearance of NLOF. From dynamical simulations of the particle performed both in the transverse plane and along the longitudinal direction, an even clearer picture of the realization of stable NLOF is presented. It is shown that, due to rotation induced by the orbital angular-momentum of light, higher order Bessel beams cannot stably confine a particle to the beam center where NLOF occurs in the absence of ambient damping, which largely limits their applications for long-distance, stable, backward particle transportation. On the other hand, zero-order Bessel beams can achieve stable transverse confinement of the manipulated particle and act as an optical tractor beam per se. In addition, for a nonmagnetic particle with relative permeability $\mu =1$, a Bessel beam with transverse electric polarization is more favorable for the realization of NLOF than a transverse magnetic beam. Finally, a brief discussion is also presented of the conditions under which an off-beam-axis particle could be suitable for backward transportation using NLOF.

The Fano line profiles, originally discovered in the context of photoionization, have been found to occur in a large class of systems such as resonators, metamaterials, and plasmonics. We demonstrate the existence of such resonances in cavity optomechanics by identifying the interfering contributions to the fields generated at anti-Stokes and Stokes frequencies. Unlike the atomic systems, the optomechanical systems provide great flexibility as the width of the resonance is controlled by the coupling field. We further show how the double cavities coupled by a single optomechanical mirror can lead to the splitting of the Fano resonance and how the second cavity can be used to tune the Fano resonances. The Fano resonances are quite sensitive to the decay parameters associated with cavities and the mechanical mirror. Such resonances can be studied by both pump probe experiments as well as the spectrum of the quantum fluctuations in the output fields.

We suggest that closed-loop quadratic nonlinear waveguide arrays can be used as a compact interferometrically stable integrated source of discrete orbital-angular-momentum (OAM) entangled biphoton state. We describe analytically and numerically the process of biphoton generation through spontaneous parametric down-conversion in triangular waveguide arrays, and reveal that the generated biphoton quantum states can be precisely controlled by changing the pump phase and wavelength, including the case of photon-pair generation with pure OAM.

We report our observation of the resonant fluorescence from highly charged uranium ions. Using the resonant coherent excitation (RCE) technique, the $2s$-$2p_{3/2}$ transition in 191.68 MeV/u Li-like U${}^{89+}$ ions was excited at 4.5 keV with a resonance width of 4.4 eV. The result demonstrated that the RCE can be applied to resonant fluorescence spectroscopy of high-$Z$ ions up to uranium with high efficiency and resolution.

We show that there exist Gaussian channels which are amendable. A channel that is entanglement-breaking of order 2 [A. De Pasquale and V. Giovannetti, Phys. Rev. A 86, 052302 (2012)] is amendable if there exists an unitary filter that, once applied in between two actions of the channel, removes the entanglement-breaking property of the overall transformation. We find that, depending on the structure of the channel, the unitary filter can be a squeezing transformation or a phase-shift operation. We also propose two realistic quantum optics experiments where the amendability of Gaussian channels can be verified by exploiting the fact that it is sufficient to test the entanglement-breaking properties of two-mode Gaussian channels on input states with finite energy (which are not maximally entangled).

We study the evolution of quantum correlations, quantified by the geometric discord, of two excitonic quantum-dot qubits under the influence of the phonon environment. We show that the decay of these correlations differs substantially from the decay of entanglement. Instead of displaying sudden-death-type behavior, the geometric discord shows a tendency to undergo transitions between different types of decay, is sensitive to nonlocal phase factors, and may already be enhanced by weak environment-mediated interactions. Hence, two-qubit quantum correlations are more robust under decoherence processes, while showing a richer and more complex spectrum of behavior under unitary and nonunitary evolution.

We report applications of the quantitative rescattering theory (QRS) for calculation of high-order-harmonic generation (HHG) from polyatomic molecules in ultrashort linearly polarized intense laser pulses, using the example of the CCl${}_4$ molecule. In particular, we present a detailed analysis and a treatment for the phase of the electron returning wave packet, which recollides with the parent molecular ion to emit high-energy photons. Our results show that Cooper-type minimum structures in the molecular photoionization cross section lead to quite distinguishable minima in the HHG spectra, even for unaligned polyatomic molecules.

We propose a platform for the investigation of quantum wave-packet dynamics, offering a complementary approach to existing theoretical models and experimental systems. It relies on laser-cooled neutral atoms which orbit around an optical nanofiber in an optical potential produced by a red-detuned guided light field. We show that the atomic center-of-mass motion exhibits genuine quantum effects like collapse and revival of the atomic wave packet. As distinctive advantages, our approach features a tunable dispersion relation as well as straightforward readout for the wave-packet dynamics and can be implemented using existing quantum optics techniques.

A parametric amplification of input signal wave in the field of broadband incoherent light is analyzed at group-velocity matching of pump and idler waves. It is shown that such group-velocity matching is possible both in Type-I and Type-II phase-matching nonlinear crystals. The appropriate conditions at which an evolution of the signal wave in the field of the incoherent pump coincides with an evolution in the field of the monochromatic pump wave are demonstrated. The large parametric gain of the signal wave which is not sensitive to pump fluctuations is feasible in Type-II phase-matching nonlinear crystals.

We performed light optical diffraction experiments on a nanoparticle-polymer volume holographic grating in an angular range including far-off-Bragg replay. A comparison of three diffraction theories, on the same level of complexity, with our experimental results shows that the dynamical theory of diffraction and the first-order two-wave coupling theory using the beta-value method fit the data very well. In contrast, the prevalent two-wave coupling theory using the K-vector closure method yields a poor fit with an order of magnitude worse mean squared error. These findings must be considered for accurate determination of coupling strength and grating thickness.

We report on high-order-harmonic generation from micrometer-sized liquid water droplets. In pump-probe experiments, the influence of the time delay onto the emission of harmonic radiation is systematically studied. Phase-matching aspects are observed by controlling the focal position and the intensity of the probe pulse. The spatiotemporal dynamics of the droplet during interaction with intense laser pulses are studied by controlling the intensity of the pump pulse. We find transient phase-matching conditions and the expansion dynamics of the droplet to be of major influence on the harmonic yield.

It has recently been pointed out that the geometric quantum discord, as defined by the Hilbert-Schmidt norm (2-norm), is not a good measure of quantum correlations, since it may increase under local reversible operations on the unmeasured subsystem. Here, we revisit the geometric discord by considering general Schatten $p$-norms, explicitly showing that the 1-norm is the only $p$-norm able to define a consistent quantum correlation measure. In addition, by restricting the optimization to the tetrahedron of two-qubit Bell-diagonal states, we provide an analytical expression for the 1-norm geometric discord, which turns out to be equivalent to the negativity of quantumness. We illustrate the measure by analyzing its monotonicity properties.

Blind quantum computation is a new quantum secure protocol, which enables Alice who does not have enough quantum technology to delegate her computation to Bob who has a fully fledged quantum power without revealing her input, output, and algorithm. So far, blind quantum computation has been considered only for the circuit model and the measurement-based model. Here we consider the possibility and the limitation of blind quantum computation in the ancilla-driven model, which is a hybrid of the circuit and the measurement-based models.