Triply differential cross sections for the electron-impact ionization of inner valence orbitals of thymine have been measured using the ($e$,2$e$) technique at an incident electron energy of 250 eV. The measurements have been performed with coplanar asymmetric kinematics for scattered electron angles of –10° and –15° and with an ejected-electron energy of 20 eV. Theoretical calculations have been performed within the first-order Born approximation and are in very good agreement with the experimental data.

A scheme is proposed to generate isolated attosecond pulses in the water window driven by a multicycle 2400-nm midinfrared laser field with moderate intensity interacting with H${}_2$${}^{+}$ molecules. Single attosecond pulses are achieved due to the charge resonance-enhanced ionization and nuclear motion by the numerical solutions of a non-Born-Oppenheimer time-dependent Schrödinger equation. Thus, the single attosecond pulse generation provides insight into the nuclear dynamics.

Using a species-selective dipole potential, we create initially localized impurities and investigate their interactions with a majority species of bosonic atoms in a one-dimensional configuration during expansion. We find an interaction-dependent amplitude reduction of the oscillation of the impurities' size with no measurable frequency shift, and study it as a function of the interaction strength. We discuss possible theoretical interpretations of the data. We compare, in particular, with a polaronic mass shift model derived following Feynman variational approach.

We theoretically investigate finite-temperature thermodynamics and demagnetization cooling of two-component Bose-Bose mixtures in a cubic optical lattice, by using bosonic dynamical mean-field theory (BDMFT). We calculate the finite-temperature phase diagram, and remarkably find that the system can be heated from the superfluid into the Mott insulator at low temperature, analogous to the Pomeranchuk effect in ${}^3$He. This provides a promising many-body cooling technique. We examine the entropy distribution in the trapped system and discuss its dependence on temperature and an applied magnetic field gradient. Our numerical simulations quantitatively validate the spin-gradient demagnetization cooling scheme proposed in recent experiments.

We derive a closed photocounting formula, including noise counts and a finite quantum efficiency, for photon-number-resolving detectors based on on-off detectors. It applies to detection schemes such as array detectors and multiplexing setups. The result renders it possible to compare the corresponding measured counting statistics with the true photon number statistics of arbitrary quantum states. The photocounting formula is applied to the discrimination of photon numbers of Fock states, squeezed states, and odd coherent states. It is illustrated for coherent states that our formula is indispensable for the correct interpretation of quantum effects observed with such devices.

We show that sine-Gordon and Bose-Hubbard dynamics with stationary polaritons could be observed in a hollow-core one-dimensional fiber loaded with a cold atomic gas. Utilizing the strong light confinement in the fiber, a range of different strongly correlated polaritonic and photonic states corresponding to both strong and weak interactions can be created and probed. The key ingredient is the creation of a tunable effective lattice potential acting on the interacting polaritonic gas, which is possible by slightly modulating the atomic density. We analyze the relevant phase diagram corresponding to the realizable Bose-Hubbard (weak) and sine-Gordon (strong) interacting regimes and conclude by describing the measurement process. The latter consists of mapping the stationary excitations to propagating light pulses whose correlations can be efficiently probed once they exit the fiber using available optical technologies.

The Fisher information $F$ gives a limit to the ultimate precision achievable in a phase estimation protocol. It has been shown recently that the Fisher information for a linear two-mode interferometer cannot exceed the number of particles if the input state is separable. As a direct consequence, with such input states the shot-noise limit is the ultimate limit of precision. In this work, we go a step further by deducing bounds on $F$ for several multiparticle entanglement classes. These bounds imply that genuine multiparticle entanglement is needed for reaching the highest sensitivities in quantum interferometry. We further compute similar bounds on the average Fisher information $\overline{F}$ for collective spin operators, where the average is performed over all possible spin directions. We show that these criteria detect different sets of states and illustrate their strengths by considering several examples, also using experimental data. In particular, the criterion based on $\overline{F}$ is able to detect certain bound entangled states.

We present several entanglement criteria in terms of the quantum Fisher information that help to relate various forms of multipartite entanglement to the sensitivity of phase estimation. We show that genuine multipartite entanglement is necessary to reach the maximum sensitivity in some very general metrological tasks using a two-arm linear interferometer. We also show that it is needed to reach the maximum average sensitivity in a certain combination of such metrological tasks.

We propose a method to obtain Floquet states—also known as light-induced states—and their quasienergies from real-time wave functions without solving the Floquet equation. This is useful for the analysis of various phenomena in time-dependent quantum dynamics if the Hamiltonian is not strictly periodic, as in short laser pulses, for instance. There, the population of the Floquet states depends on the pulse form and is automatically contained in the real-time wave function but not in the standard Floquet approach. Several examples in the area of intense laser-atom interaction are exemplarily discussed: (i) the observation of even harmonics for an inversion-symmetric potential with a single bound state; (ii) the dependence of the population of Floquet states on (gauge) transformations and the emergence of an invariant, observable photoelectron spectrum; (iii) the driving of resonant transitions between dressed states, (i.e., the dressing of dressed states), and (iv) spectral enhancements at channel closings due to the ponderomotive shift of above-threshold ionization peaks.

Core-valence double photoionization electron spectra of the SO${}_2$ molecule involving the S 2$p$ and O 1$s$ inner shells have been measured using a time-of-flight multiparticle coincidence technique. The experimental spectra are compared with quantum-chemical calculations based on density functional theory by which several core-valence dicationic states are identified. Assignments conform with a picture where the formation of a O 1$s$-valence dicationic state is associated with a physical, “pseudo-Jahn-Teller,” symmetry breaking and core-hole localization. It is shown that while density functional theory gives very good transition energies in the symmetry-broken case, it gives a poor representation in the symmetry-restricted case, and an incomplete account of the Hartree-Fock localization energy.

Current techniques based on x-ray or electron diffraction are successfully employed for structure determination in condensed matter but are sometimes limited when applied to low density media such as the gas phase. Here we show that vibrationally resolved photoelectron spectroscopy based on x rays generated by third generation synchrotron light sources can be used to infer the structure of isolated molecules in a simple and efficient way. In particular, we show that vibrational ratios obtained from inner shell C 1$s$ photoelectron spectroscopy of isolated methane molecules exhibit pronounced oscillations that are the fingerprints of electron diffraction by the surrounding atomic centers, thus providing the necessary information for the determination of the molecular geometry.

We study finite-temperature phase structures of hard-core bosons in a two-dimensional optical lattice subject to an effective magnetic field by employing the gauged CP${}^1$ model. Based on the extensive Monte Carlo simulations, we study their phase structures at finite temperatures for several values of the magnetic flux per plaquette of the lattice and mean particle density. Despite the presence of the particle number fluctuation, the thermodynamic properties are qualitatively similar to those of the frustrated $XY$ model, with only the phase as a dynamical variable. This suggests that cold-atom simulators of the frustrated $XY$ model are available irrespective of the particle filling at each site.

A theoretical model is developed describing high-order-harmonic generation (HHG) from a gas of multiply charged ions driven by a laser field of relativistic intensity. Macroscopic propagation of harmonics is investigated in a relativistic HHG setup where the relativistic drift is suppressed by means of x-ray field assistance of the driving laser field. The possibility of phase-matched emission of the harmonics is shown. The laser field geometry is optimized to maximize the HHG yield with the corresponding phase-matching schemes. Crucial issues determining the macroscopic HHG yield are discussed in detail.

Entanglement of formation for arbitrary mixed states in a ($2\otimes 2$)-dimensional Hilbert space is well known. For higher-dimensional mixed states analytical expressions for quantifying entanglement exist for a particular family of states. In this work, we calculate analytically the entanglement of formation for a family of bipartite ($2\otimes d$)-dimensional mixed states which can be obtained from tripartite $2\otimes 2\otimes d$ pure states following the entanglement relations obtained by Koashi and Winter [Phys. Rev. A 69, 022309 (2004)].

We develop an efficient numerical procedure for solving the scattering problem on one-electron diatomic molecules in the fixed-nuclei approximation. For this purpose, we use the $R$-matrix propagation method together with the discrete variable representation method in prolate spheroidal coordinates. The demonstrated elastic scattering differential cross sections and the photoionization differential cross sections for H${}_2^{+}$ and HeH${}^{2+}$ exhibit oscillating structures owing to the two-center nature of the molecules. We analyze them by using the Coulomb corrected independent-atom model to identify the two-center quantum interference, and it is found that multiple-scattering effects become important in the heteronuclear system.

We show how to calculate the first- and second-order statistics of the scattered fields for an arbitrary intensity coherent-state light field interacting with a two-level system in a waveguide geometry. Specifically, we calculate the resonance fluorescence from the qubit, using input-output formalism. We derive the transmission and reflection coefficients, and illustrate the bunching and antibunching of light that is scattered in the forward and backward directions, respectively. Our results agree with previous calculations on one- and two-photon scattering as well as those that are based on the master equation approach.

A detailed description and theoretical analysis of experiments achieving coherent coupling between an ion Coulomb crystal and an optical cavity field are presented. The various methods used to measure the coherent coupling rate between large ion Coulomb crystals in a linear quadrupole radiofrequency ion trap and a single-field mode of a moderately high-finesse cavity are described in detail. Theoretical models based on a semiclassical approach are applied in assessment of the experimental results of P. F. Herskind et al.[Nature Phys. 5, 494 (2009)] and of complementary new measurements. Generally, a very good agreement between theory and experiments is obtained.

We present a scheme for generating entanglement between two qubits associated with a pair of particles, which move and interact, in a one-dimensional harmonic-oscillator potential. The spatial wave functions of the particles are initially localized on either side of the oscillator. As they “fall” toward each other, we find that the interaction between the two particles produces an effective exchange interaction between the qubits. This allows us to produce a “power-of-swap” operation on the initial two-qubit quantum state without requiring any time-dependent control. We find that under certain conditions, we can generate maximally entangled states from a product state with a fidelity that is only weakly dependent on initialization errors.

This paper is dedicated to the implementation of a generalized approach for calculating quantum defects in high Rydberg states of polar molecules with an account for the dipole moment of the molecular core and $l$ uncoupling of the Rydberg electron. Adiabatic (Born-Oppenheimer) and nonadiabatic (inverse Born-Oppenheimer) regions of the spectrum are considered. The nonadiabatic case with a nonzero projection of the core momentum on the core axis is considered and is illustrated by the example of the SO molecule.

We present exact solutions of a two-body problem for spin-$1/2$ fermions with isotropic spin-orbit (SO) coupling and interacting with an arbitrary short-range potential. We find that in each partial-wave scattering channel, the parametrization of a two-body wave function at short interparticle distance depends on the scattering amplitudes of all channels. This reveals the mixed-partial-wave scattering induced by SO couplings. By comparing with results from a square-well potential, we investigate the validity of original pseudopotential models in the presence of SO coupling. We find the $s$-wave pseudopotential provides a good approximation for low-energy solutions near $s$-wave resonances, given the length scale of SO coupling much longer than the potential range. However, near $p$-wave resonance the $p$-wave pseudopotential gives low-energy solutions that are qualitatively different from exact ones, based on which we conclude that the $p$-wave model can not be applied to the fermion system if the SO coupling strength is larger or comparable to the Fermi momentum.