Table of contents

Using electron and ion spectroscopy, we studied the electron and nuclear dynamics in ∼50 000-atom large krypton clusters, following excitation with an intense hard x-ray pulse. Beyond the single pulse experiment, we also present the results of a time-resolved, x-ray pump–near-infrared probe measurement that allows one to learn about the time evolution of the system. After core ionization of the atoms by x-ray photons, trapped Auger and secondary electrons form a nanoplasma in which the krypton ions are embedded, according to the already published scenario. While the ion data show expected features, the electron emission spectra miss the expected pump–probe delay-dependent enhancement except for a slight enhancement in the energy range below 2 eV. Theoretical simulations help to reveal that, due to the deep trapping potential of the ions during the long time expansion accompanied by electron–ion recombination, thermal emission from the transient nanoplasma becomes quenched.

The multifrequency resonance has been widely explored in the context of single-particle models, of which the modulating Rabi model has been the most widely investigated. It has been found that with diagonal periodic modulation, steady dynamics can be realized in some well-defined discrete frequencies. These frequencies are independent of off-diagonal couplings. In this work, we generalize this physics to the many-body seesaw realized using the tilted Bose–Hubbard model. We find that the wave function will recover to its initial condition when the modulation frequency is commensurate with the initial energy level spacing between the ground and the first excited levels. The period is determined by the driving frequency and commensurate ratio. In this case, the wave function will be almost exclusively restricted to the lowest two instantaneous energy levels. By projecting the wave function to these two relevant states, the dynamics is exactly the same as that for the spin precession dynamics and nutation dynamics around an oscillating axis. We map out the corresponding phase diagram, and show that, in the low-frequency regime, the state is thermalized, and in the strong modulation limit, the dynamics is determined by the effective Floquet Hamiltonian. The measurement of these dynamics from the mean position and mean momentum in phase space are also discussed. Our results provide new insights into multifrequency resonance in the many-body system.

Rydberg levels in atomic calcium are of interest due to their use in highly isotope selective multiple-step resonance ionisation spectrometry, and also for nuclear physics investigations, but gaps remain in the data for higher lying levels in calcium isotopes other than ${}^{40}\text{Ca}$. We report novel isotope shift data on four isotopes of calcium (${}^{42}\text{Ca}$, ${}^{43}\text{Ca}$, ${}^{44}\text{Ca}$, ${}^{48}\text{Ca}$), relative to the majority abundance isotope ${}^{40}\text{Ca}$, in six Rydberg transitions for each P (n = 25–30) and F (n = 23–28) angular momentum quantum number designated series.

The K-shell ionization cross sections of titanium and copper atoms were determined by analyzing the spectra of characteristic X-ray radiation generated by an electron beam with energies of 1 and 2 GeV in metal foils. New data obtained for these energies demonstrate the influence of the density effect on the ionization cross sections values. The results were compared with previous experimental data and calculations based on pure theoretical and semi-empirical models.

Inelastic fine rotational cross-sections of the magnesium monohydroxide (MgOH) molecule by collision with helium (He) atoms are investigated. We illustrate the two-dimensional potential energy surface (2D-PES) for the MgOH–He interacting system. The ab initio 2D-PES is computed using the restricted coupled cluster approach with single, double, and perturbative triple excitation connected to an augmented-correlation consistent-polarized valence quadruple zeta Gaussian basis set. One minimum located at (θ = 0°; R = 8.25 bohr) on the side of the hydrogen atom is observed. Inelastic cross-sections are investigated for the 13 first fine rotational levels for a total energy up to 100 cm⁻¹. Propensity rules toward odd ΔN and ΔN = Δj are found.

We study the phase separation configurations and rotational properties of a mixture of two interacting charged Bose–Einstein condensates subjected to a magnetic field trapped in disc and Corbino geometries. We calculate the ground state energies of the azimuthal and radial phase separation configurations using the Gross–Pitaevskii and Thomas–Fermi approximations. We show that the results for the experimentally relevant system parameters of both approaches are in good agreement. For both geometries, an immiscible mixture with equal intracomponent interactions favors azimuthal phase separation for all intercomponent interactions. Only an imbalance in the intracomponent interactions can result in a transition to radial phase separation, for which the transition becomes sensitive to the shape of the trap. We present phase diagrams as functions of the inter- and intracomponent interactions. While radial phase separation is widely favoured in disc geometry, the azimuthal phase separation is favoured for narrower Corbino geometries. We explore the rotational properties of spatially separated condensates subjected to magnetic fields, studying their angular momenta and velocity fields. The quantization of circulation breaks down for azimuthal phase separation. In this case, the bulk region of the condensate continues to display superfluid flow behaviour, whereas the velocity field shows a rigid body behaviour along the phase boundaries.

A quantum electrodynamical theory for single-photon diffraction of light from a mesoscopic hole in a quantum well (QW) screen with (Schrödinger) electron dynamics is established. Photon wave mechanics (PWM) is used to extend and bridge the gap between hitherto used semiclassical and quantum optical theoretical approaches for analyses of diffraction of light. An essentially complete calculation is carried out for a paradigm example: (i) a single-photon point-like electric-dipole (ED) primary source, emitting (ii) a wave packet photon toward (iii) a two-level QW screen possessing (iv) in-plane jellium electrodynamics with (v) a single mesoscopic ED hole. The PWM description is based on the, in this context attractive, Riemann–Silberstein–Oppenheimer–Bialynicki formulation. The effective size of the hole is determined on the basis of a quantum mechanical extinction theorem for the in-plane jellium electron dynamics in the vicinity of the hole. The incident electrodynamic field induced current density in the screen (with hole) allows one to obtain the single-photon probabilities for scattering from the hole and the screen. A one-photon wave train emitted by the primary ED point-like source is assumed to drive the scattering process. The far-field hole-screen diffraction pattern is calculated paying particular attention to the spectral diffraction (correlation) pattern, which illustrates the interplay between the wave-train frequency, the screen/hole local-field resonance frequency, and the Bohr frequency. Our theory shows that the ED hole polarizability is close to that of a one-dimensional single harmonic oscillator with resonance frequency coinciding with the local-field resonance in the two-level QW screen.

A target whispering-gallery-mode microresonator (WGMM) directly coupled to a waveguide with an auxiliary side-coupled WGMM is proposed to deterministically extract both the resonant and non-resonant single incident photons from a waveguide. Based on the single-photon Raman interaction (SPRINT) between an Λ-type three-level atom and the target WGMM, a full quantum theory in real space is adopted to calculate the extraction efficiencies at the single-photon level. The results show that the extraction efficiencies can be significantly improved by appropriately tuning the frequencies of the auxiliary WGMM and the coupling strength between the two WGMMs, even when the atom and WGMMs have dissipations. Since mode redistribution is only externally imposed on the auxiliary WGMM, the population and phase of the atom are not directly affected. The nonlocal control, which ensures that the SPRINT takes place, results in high extraction efficiencies. We also find that the transmission probabilities of both the resonant and non-resonant incident photons can be controlled in a range from 0 to 100%, so that the proposed double-WGMM system has the potential to be used as a single-photon switch.

We report experimental and theoretical results of two symmetrical signals of degenerate four-wave mixing generated in rubidium vapor. Both nonlinear signals are induced by two almost copropagating laser beams, with ${ \overrightarrow {k}}_{a}$ and ${ \overrightarrow {k}}_{b}$ wave-vectors, and detected simultaneously in the $2{ \overrightarrow {k}}_{a}-{ \overrightarrow {k}}_{b}$ and $2{ \overrightarrow {k}}_{b}-{ \overrightarrow {k}}_{a}$ directions. In each direction, we observe a single peak when the two beams are tuned on the closed transition ⁸⁵Rb 5S_1/2(F = 3) → 5P_3/2(F = 4). The excitation spectra reveal a small frequency separation between the two peaks, which is explained when propagation effects are taken into account. Furthermore, our theoretical analysis shows that a correct description of the frequency position of each peak is achieved with a variable refractive index for both lasers, in which the scanning laser experiences an anomalous window in the refractive index near resonance.

Discrete modulation can make up for the shortage of transmission distance in measurement-device-independent continuous-variable quantum key distribution (MDI-CVQKD), providing a unique advantage against all side-channel attacks but also creating a challenge for further performance improvement. Here we suggest a quantum catalysis (QC) approach for enhancing the performance of the discrete-modulated (DM) MDI-CVQKD in terms of the achievable secret key rate and lengthening the maximal transmission distance. The numerical simulation results show that the QC-based MDI-CVQKD with discrete modulation, involving a zero-photon catalysis (ZPC) operation, can not only obtain a higher secret key rate than the original DM protocol, but also contribute to a reasonable increase of the corresponding optimal variance. As for the extreme asymmetric and symmetric cases, the secret key rate and maximal transmission distance of the ZPC-involved DM MDI-CVQKD system can be further improved under the same parameters. This approach enables the system to tolerate lower reconciliation efficiency, which may provide excellent potential for practical implementations with state-of-art technology.

This paper investigates the generation of quantum entanglement by means of conditional stimulated Raman adiabatic passage (STIRAP) based on Rydberg blockade. The paper compares the entanglement fidelities in three-level and four-level schemes and analyzes the adiabatic conditions in both cases. In particular, Green–Horne–Zeilinger states can be deterministically generated in an atomic ensemble interacting with a single control atom.

An effective semi-classical method is introduced for controlling the high-order harmonic generation process and extending the cutoff frequency. This method is capable of defining the proper specification of the driving laser for maximizing the cutoff frequency. This method is evaluated by examining the high harmonic spectrum from the hydrogen atom and the fluorine (F₂) molecule irradiated by single-, two-, and three-color laser fields. This study is done using the time-dependent density functional theory in a three-dimensional space. The results show that the single-, two-, and three-color laser pulses tuned by proper specifications could extend the cutoff frequency by up to 85%, 176%, and 241% compared to their non-tuned forms, respectively. Also, single attosecond pulses with a duration of 161 as and 129 as are obtained by applying the tuned three-color laser for the hydrogen atom and the fluorine molecule, respectively.