We have studied the multielectron processes in close collisions between slow ${\mathrm{Ne}}^{q+}$ ions ($q=1–9$, energies of 5 and $14\mathrm{keV}$) and Ar atoms through measurements of the charge-state correlations between 27° scattered and 70° recoiling ions. At the selected scattering angle, the internuclear distance of the closest approach at $35\mathrm{keV}$ is comparable to the $L$-shell radius of Ar atoms. A drastic difference between low-charged $(q=1–3)$ and highly charged $(q=7–9)$ Ne ions was found. For example, the most probable channel for the ${\mathrm{Ne}}^{7+}$ projectile is three-electron capture accompanied with two-electron loss whereas for the ${\mathrm{Ne}}^{+}$ projectile pure double ionization was found most probable. As a general trend, the mean charges of the both ions and the mean number of captured electrons increase almost linearly with incident charge $q$, while the mean number of ejected electrons from the system is independent of $q$ at both 5 and $14\mathrm{keV}$. We also measured the charge state distributions of the Ar recoil ions as function of the ${\mathrm{Ne}}^{q+}$ ($q=3$, 5, and 7) energies between 5 and $63\mathrm{keV}$, which corresponds to distances of closest approach between $0.6\mathrm{a.u.}$ and $0.17\mathrm{a.u.}$ We found that the charge of the Ar ions increases at internuclear distances less than $0.32\mathrm{a.u.}$

We present a theoretical study of the electron angular distribution produced in resonance enhanced two-photon ionization of the $\mathrm{H}_2{}^{+}$ molecular ion using ultrashort laser pulses. The method consists in solving the time dependent Schrödinger equation and includes all electronic and vibrational degrees of freedom. Differential (in proton energy and electron emission solid angle) ionization probabilities have been evaluated for various photon energies, laser intensities, and pulse durations. We show that $(1+1)$ resonance-enhanced multiphoton ionization (REMPI) leads to angular distributions significantly different from those produced in direct two-photon ionization. The REMPI process is observed even at photon energies not matching the energy difference between two electronic states in a perfect vertical transition. Interestingly, there is no trace of REMPI effects in the electron angular distribution when the fully differential probabilities are integrated over proton energy.

We describe a technique for transferring a two-level atom between two adjacent potential wells of an optical lattice, using pairs of pump and Stokes pulses, each resonantly coupling the same pair of internal atomic states to form a Raman transition. Starting from a vibrational eigenstate of one well the atom slowly moves under the action of the pulse pair, to the vibrational eigenstate with the same quantum number in the neighboring well. The transfer takes place in two stages: A conventional stimulated Raman adiabatic passage (STIRAP) technique, in which Stokes precedes pump pulse, is followed by a pulse sequence where pump precedes Stokes and with an inverted sign of the Stokes envelope. In the first step the atom is accelerated toward the adjacent well and in the second step decelerated to the initial vibrational energy. The STIRAP technique avoids the introduction of stochastic motion caused by spontaneous emission from the excited internal atomic state.

Using stationary solutions of the linearized two-dimensional Gross-Pitaevskii equation, we describe the wave pattern occurring in the supersonic flow of a Bose-Einstein condensate past an obstacle. It is shown that these waves are generated outside the Mach cone. The developed analytical theory is confirmed by numerical simulations of the flow past body problem in the frame of the full nonstationary Gross-Pitaevskii equation. Relation of the developed theory with recent experiments is discussed.

The first-order quantum corrections to the static structure factor of vortex lattices in a rapidly rotating quasi-two-dimensional Bose-Einstein condensate are calculated. Furthermore, we estimate the melting filling fraction by using a criterion similar to that used in thermal melting related to the Debye-Waller factor of the smallest reciprocal lattice vector.

A two-mode single-atom laser is considered, with the aim of generating entanglement in macroscopic light. Two transitions in the four-level gain medium atom independently interact with the two cavity modes, while two other transitions are driven by control laser fields. Atomic relaxation as well as cavity losses are taken into account. We show that this system is a source of macroscopic entangled light over a wide range of control parameters and initial states of the cavity field.

We report the direct observation of phase locking between adjacent pulses in an attosecond pulse train (APT) via interferometric autocorrelation (IAC). In this measurement, the Coulomb explosion of ${\mathrm{N}}_2$ caused by two-photon absorption is utilized as correlated signals between two replicas of the APT that are the outcome of the spatial division of the APT in the interferometer. The analysis of IAC by the spatial division of the APT is consistent with the experimental trace of the IAC, and yields the duration of the pulse in the APT of $320\text{attoseconds}$, which corresponds to a $1.3\text{cycle}$ period of the carrier frequency of the harmonic field.

A scheme for implementing a three-qubit Toffoli gate with atoms sent through a microwave cavity is proposed by choosing nonidentical coupling constants between the atoms and cavity. The scheme can be generalized to implement an $N$-qubit Toffoli gate and the gating time does not change with an increase of the number of qubits.

We propose a scheme to generate cluster states of atomic qubits by using cavity quantum electrodynamics (QED) and linear optics, in which each atom is confined in a resonant optical cavity with two orthogonally polarized modes. Our scheme is robust to imperfect factors such as dissipation, photon loss, and detector inefficiency. We discuss the experimental feasibility of our scheme.

We report on a measurement of the ${\pi }^{-}$ nuclear capture ratio on hydrogen and oxygen in water by two methods. The capture ratio is measured to be $W_{{\mathrm{H}}_2\mathrm{O}}=(4.45\pm 0.24)\times {10}^{-3}$.

The photoionization of free Xe clusters is investigated by angle-resolved time-of-flight photoelectron spectroscopy. The measurements probe the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. While the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the free atoms, distinct differences in the angular distribution point at cluster-size-dependent effects. Multiple scattering calculations trace their origin to elastic photoelectron scattering.

In a rotating two-component Bose-Einstein condensate (BEC), the traditional triangular vortex lattice can be replaced by a rectangular vortex lattice or even a structure characterized in terms of vortex sheets, depending on the interspecies interactions. We study the dynamics of this system by analyzing the Bogoliubov excitation spectrum. Excitations familiar to BEC vortex systems are found such as Tkachenko modes, hydrodynamic modes, and surface waves, however, the complex two-component morphology also gives rise to phenomena including shear flow between vortex sheets.

The equation of state of a dilute two-component asymmetric Fermi gas at unitarity is subject to strong constraints, which affect the spatial density profiles in atomic traps. These constraints require the existence of at least one nontrivial partially polarized (asymmetric) phase. We determine the relation between the structure of the spatial density profiles and the $T=0$ equation of state, based on the most accurate theoretical predictions available. We also show how the equation of state can be determined from experimental observations.

Decoherence induced by coupling a system with an environment may display universal features. We demonstrate that when the coupling to the system drives a quantum phase transition in the environment, the decay of quantum coherences in the system is Gaussian with a width independent of the system-environment coupling strength. We obtain analytical results for a class of solvable models, and present numerical evidence supporting the validity of our results in more general cases. This effect opens the way for a quantum simulation algorithm, where a single qubit is used to detect a quantum phase transition. We discuss possible implementations of such an algorithm and relate our results to available data on universal decoherence in NMR echo experiments.

We describe a method in which the entanglement of any pure quantum state can be experimentally determined by a simple projective measurement, provided the state is available in a twofold copy. We propose implementations of this approach for various systems and discuss in detail its first experimental realization, which employed twin photons entangled in two degrees of freedom, prepared in identical polarization and momentum states. We analyze the effect of errors due to imperfect state preparation.

The parity gate emerged recently as a promising resource for performing universal quantum computation with fermions using only linear interactions. Here we analyze the parity gate ($P$ gate) from a theoretical point of view in the context of quantum networks. We present several schemes for entanglement generation with $P$ gates and show that native networks simplify considerably the resources required for producing multiqubit entanglement, such as $n$–Greenberg-Horne-Zellinger (GHZ) states. Other applications include a Bell-state analyzer and teleportation. We also show that cluster state fusion can be performed deterministically with parity measurements. We then extend this analysis to hybrid quantum networks containing spin and mode qubits. Starting from an easy-to-prepare resource (spin-mode entanglement of single electrons) we show how to produce a spin $n$-GHZ state with linear elements (beam splitters and local spin flips) and charge-parity detectors; this state can be used as a resource in a spin quantum computer or as a precursor for constructing cluster states. Finally, we construct an alternative spin-controlled-$Z$ gate by using the mode degrees of freedom as ancillæ.

We present an analysis of the entanglement characteristics in the Majumdar-Ghosh (MG) or $J_1-J_2$ Heisenberg model. For a system consisting of up to 28 spins, there is a deviation from the scaling behavior of the entanglement entropy characterizing the unfrustrated Heisenberg chain above $J_2\approx 0.25$. This feature can be used as an indicator of the dimer phase transition occurring in this model. Additionally, we also consider entanglement at the MG point $J_2=0.5J_1$.

Extreme-ultraviolet spectra of xenon ions have been recorded in the 4.5 to $20\mathrm{nm}$ wavelength region using an electron beam ion trap and a flat field spectrometer. The electron beam energy was varied from $180\mathrm{eV}$ to $8\mathrm{keV}$ and radiation from charge states ${\mathrm{Xe}}^{6+}$ to ${\mathrm{Xe}}^{43+}$ was observed. Our measured wavelengths were compared to atomic structure calculations using the Cowan suite of codes. We have measured seventeen previously unreported features corresponding to transitions in ${\mathrm{Xe}}^{35+}$ through to ${\mathrm{Xe}}^{41+}$ with estimated wavelength uncertainties of $\pm 0.003\mathrm{nm}$. It was found that for the case of continuous injection of neutral xenon gas a wide range of charge states were always present in the trap but this charge state distribution was greatly narrowed, towards higher charge states, if a sufficiently low gas injection pressure was employed. The energy dependence of spectral lines arising from ${\mathrm{Xe}}^{42+}$ and ${\mathrm{Xe}}^{43+}$ revealed enhancement of the total ionization cross sections, due to excitation-autoionization of $n=2$ electrons to $n=3$ levels, in the ${\mathrm{Xe}}^{41+}$ and ${\mathrm{Xe}}^{42+}$ charge states.

We describe the effect of pure dephasing upon the time-dependent dynamics of two-state quantum systems in the framework of a Lindblad equation for the time evolution of the density matrix. A uniform approximate formula is derived, which modifies the corresponding lossless transition probability by an exponential factor containing the dephasing rate and the interaction parameters. This formula is asymptotically exact in both the diabatic and adiabatic limits; comparison with numerical results shows that it is highly accurate also in the intermediate range. Several two-state models are considered in more detail, including the Landau-Zener, Rosen-Zener, Allen-Eberly, and Demkov-Kunike models, along with several other models, such as a Gaussian model and a Landau-Zener model with a pulsed coupling.

Weak interactions within a nucleus generate a nuclear spin dependent, parity-violating electromagnetic moment, the anapole moment. We analyze a method to measure the nuclear anapole moment through the electric dipole transition it induces between hyperfine states of the ground level. The method requires tight confinement of the atoms to position them at the antinode of a standing wave Fabry-Perot cavity driving the anapole-induced microwave $E1$ transition. We explore the necessary limits in the number of atoms, excitation fields, trap type, interrogation method, and systematic tests necessary for such measurements in francium, the heaviest alkali.