We report triply differential measurements of atomic hydrogen ionization by 17.6-eV electrons, with the outgoing electrons both having 2 eV energy. These measurements supersede some of the existing data. The complete set is critically analyzed and is found to be much more internally consistent than before, thereby providing one of the most stringent tests for theory to date. Comparison with the calculations from the exterior complex scaling and convergent close-coupling theories shows excellent overall agreement in both shapes and magnitude.

We discuss three-body processes in ultracold two-component Fermi gases with short-range intercomponent interaction characterized by a large and positive scattering length a. It is found that in most cases the probability of three-body recombination is a universal function of the mass ratio and a, and is independent of short-range physics. We also calculate the scattering length corresponding to the atom-dimer interaction.

The optical response of a moving medium suitably driven into a slow-light propagation regime strongly depends on its velocity. This effect can be used to devise a scheme for imaging ultraslow velocity fields. The scheme turns out to be amenable to study in situ the dynamics of collective and topological excitations of a trapped Bose-Einstein condensate. We illustrate how slow-light imaging works specifically for sloshing oscillations and bent vortices in a stirred condensate.

In this paper we determine the magnitude of phase fluctuations caused by atom-atom interaction in a one-dimensional beam of bosonic atoms. We imagine that the beam is created with a large coherence length, and that interactions only act in a specific section of the beam, where the atomic density is high enough to validate a Bogoliubov treatment. The magnitude and coherence length of the ensuing phase fluctuations in the beam after the interaction zone are determined.

Among the many proposals for the realization of a quantum computer, holonomic quantum computation is distinguished from the rest as it is geometrical in nature and thus expected to be robust against decoherence. Here we analyze the realization of various quantum gates by solving the inverse problem: Given a unitary matrix, we develop a formalism by which we find loops in the parameter space generating this matrix as a holonomy. We demonstrate that such a one-qubit gate as the Hadamard gate and such two-qubit gates as the controlled-NOT gate and the SWAP gate, and the discrete Fourier transformation can be obtained with a single loop.

Quantum discord was proposed as an information-theoretic measure of the “quantumness” of correlations. I show that discord determines the difference between the efficiency of quantum and classical Maxwell’s demons—that is, entities that can or cannot measure nonlocal observables or carry out conditional quantum operations—in extracting work from collections of correlated quantum systems.

We propose a generalized discrimination scheme for mixed quantum states. In the present scenario we allow for certain fixed fraction of inconclusive results and we maximize the success rate of the quantum-state discrimination. This protocol interpolates between the Ivanovic-Dieks-Peres scheme and the Helstrom one. We formulate the extremal equations for the optimal positive operator valued measure describing the discrimination device and establish a criterion for its optimality. We also devise a numerical method for efficient solving of these extremal equations.

Quantum entanglement in multipartite systems cannot be shared freely. In order to illuminate basic rules of entanglement sharing between qubits, we introduce a concept of an entangled structure (graph) such that each qubit of a multipartite system is associated with a point (vertex), while a bipartite entanglement between two specific qubits is represented by a connection (edge) between these points. We prove that any such entangled structure can be associated with a pure state of a multiqubit system. Moreover, we show that a pure state corresponding to a given entangled structure is a superposition of vectors from a subspace of the $2^N$-dimensional Hilbert space, whose dimension grows linearly with the number of entangled pairs.

We propose a generalization of quantum teleportation: the so-called many-to-many quantum communication of the information of a d-level system from N spatially separated senders to $M>N$ receivers situated at different locations. We extend the concept of asymmetric telecloning from qubits to d-dimensional systems. We investigate the broadcasting of entanglement by using local $\overrightarrow{1}2$ optimal universal asymmetric Pauli machines and show that the maximal fidelities of the two final entangled states are obtained when symmetric machines are applied. Cloning of entanglement is studied using a nonlocal optimal universal asymmetric cloning machine and we show that the symmetric machine optimally copies the entanglement. The “many-to-many” teleportation scheme is applied in order to distribute entanglement shared between two observers to two pairs of spatially separated observers.

The interpretation of the entropy sum as a correlation measure is demonstrated for isoelectronic series via an analytical expression that models the asymptotic behavior of the electronic charge density in position space and the cusp behavior in momentum space. We also develop an expression for the entropy sum in neutral atoms with an explicit dependence on the ionization energy and the atomic number. The results obtained from these relations are in qualitative agreement with the behavior observed from ab initio calculations. A connection between the entropy sum and the correlation energy is obtained for the weakly inhomogeneous electron gas and demonstrated via calculations for the helium isoelectronic series.

Using a high-efficiency, transmission grating spectrometer at an electron-beam ion trap, the ${3s}^2{3p}^6{3d}^4$ $J=2\mathrm{}–3$ transition in the ground configuration of the Ti-like ions ${\mathrm{Pt}}^{56+},$ ${\mathrm{Au}}^{57+},$ and ${\mathrm{Tl}}^{59+}$ was measured. The measurements achieved up to 20 times better precision than previously reported other high-$Z$ measurements.

The limiting temperature achieved by sympathetic cooling in an rf trap is calculated with a theoretical model in which no fitting parameters are used. The calculated result agrees well with observation. The dependence of the temperature on trapping parameters and ion mass is also analyzed. The results can be used for designing an rf trap system.

Picosecond half cycle pulses (HCPs) have been used to examine the effect of transient electric fields on the autoionization of doubly excited states of calcium. The autoionization yield, following picosecond isolated core excitation (ICE) of $4pnd$ Rydberg states, has been measured as a function of the relative delay between the transient field and the ICE laser pulse. Using single and multiple HCPs in combination with a static electric field, we explicitly investigate the relative importance of static field induced $\mathcal{l}$ mixing, and transient field excitation of high-$\mathcal{l},$ low-$m$ or high-$\mathcal{l},$ high-$m$ states on the suppression of autoionization. Our experimental results can be understood using semiclassical analyses and are well reproduced by quantum simulations.

We present an introduction to phase-space techniques (PST) based on a quantum-field-theoretical (QFT) approach. In addition to bridging the gap between PST and QFT, our approach results in a number of generalizations of the PST. First, for problems where the usual PST do not result in a genuine Fokker-Planck equation (even after phase-space doubling) and hence fail to produce a stochastic differential equation (SDE), we show how the system in question may be approximated via stochastic difference equations $\left(\mathrm{S}\Delta \mathrm{E}\right).\mathrm{}$ Second, we show that introducing sources into the SDE’s (or $\mathrm{S}\Delta \mathrm{E}\mathrm{’}\mathrm{s})$ generalizes them to a full quantum nonlinear stochastic response problem (thus generalizing Kubo’s linear reaction theory to a quantum nonlinear stochastic response theory). Third, we establish general relations linking quantum response properties of the system in question to averages of operator products ordered in a way different from time normal. This extends PST to a much wider assemblage of operator products than are usually considered in phase-space approaches. In all cases, our approach yields a very simple and straightforward way of deriving stochastic equations in phase space.

It is well known that in a laser—in the limit of an infinite extent of the transverse aperture—traveling tilted waves are excited at the laser threshold for positive detuning between the frequency of the gain maximum of the active medium and the cavity frequency [Phys. Rev. A 45, 8129 (1992)]. However, a transverse standing wave is unstable. In this paper, it is shown that in anisotropic lasers there can be a chain of secondary bifurcations very close to threshold, which stabilizes the standing wave and then destabilizes it again through a supercritical Hopf bifurcation. The parameter dependence of these bifurcations is discussed. The investigations are motivated by interest in pattern formation in vertical-cavity surface-emitting lasers in which the rotational symmetry is broken due to the dependence of the reflectance of the Bragg reflectors on the polarization vector of the field. The applicability of the results to other class-B lasers is discussed.

Operators that are associated with several important quantities, such as angular momentum, play a double role: they are both generators of the symmetry group and “observables.” The analysis of different splittings of angular momentum into “spin” and “orbital” parts reveals the difference between these two roles. We also discuss a relation of different choices of spin observables to the violation of Bell inequalities.

A scheme for teleporting an arbitrary three-particle state is proposed when three pairs of entangled particles are used as quantum channels. Quantum teleportation can be successfully realized with a certain probability if the receiver adopts an appropriate unitary-reduction strategy. The probability of successful teleportation is determined by the smallest coefficients of the three entangled pairs.

A time-dependent Kohn-Sham-(KS-)like theory is presented for N bosons in three- and lower-dimensional traps. We derive coupled equations, which allow us to calculate the energies of elementary excitations. A rigorous proof is given to show that the KS-like equation correctly describes the properties of one-dimensional impenetrable bosons in a general time-dependent harmonic trap in the large-N limit.

There have been theoretical and experimental studies on quantum nonlocality for continuous variables, based on dichotomic observables. In particular, we are interested in two cases of dichotomic observables for the light field of continuous variables: One case is even and odd numbers of photons and the other case is no photon and the presence of photons. We analyze various observables to give the maximum violation of Bell’s inequalities for continuous-variable states. We discuss an observable which gives the violation of Bell’s inequality for any entangled pure continuous-variable state. However, it does not have to be a maximally entangled state to give the maximal violation of Bell’s inequality. This is attributed to a generic problem of testing the quantum nonlocality of an infinite-dimensional state using a dichotomic observable.

A given density matrix may be represented in many ways as a mixture of pure states. We show how any density matrix may be realized as a uniform ensemble. It has been conjectured that one may realize all probability distributions that are majorized by the vector of eigenvalues of the density matrix. We show that if the states in the ensemble are assumed to be distinct then this is not true, but a marginally weaker statement may still be true.