An 11-state close-coupling calculation for the interaction between a slow electron and atomic iodine is carried out using the fully relativistic $R$-matrix method. The cross sections are presented for the photodetachment of a negative atomic iodine ion and for electron scattering by neutral atomic iodine from the threshold to $8\mathrm{eV}$. The electron affinity for negative iodine is obtained as $2.958\mathrm{eV}$. For the photodetachment process, we get fairly good agreement with experimental results for the distinct spin-orbit split between the $5p_{3∕2}$ and $5p_{1∕2}$ thresholds due to the relativistic effect as well as for the cross sections near the thresholds. The electron scattering cross sections display energy dependence similar to that for electron scattering by heavy rare-gas atoms, i.e., a Ramsauer-Townsend minimum well at a lower energy and a broad peak after the well.

Wave-particle duality finds a natural application for electrons or light propagating in disordered media where coherent corrections to transport are given by two-wave interference. For scatterers with internal degrees of freedom, these corrections are observed to be much smaller than would be expected for structureless scatterers. By examining the basic example of the scattering of one photon by two spin-1/2 atoms—a case study for coherent backscattering—we demonstrate that the loss of interference strength is associated with which-path information stored by the scattering atoms.

We present a modification of the standard single-item quantum search procedure that acquires robustness from spontaneous decay of the qubits. This damps the usual oscillation of populations, driving the system to a steady state with a strongly enhanced population of the solution. Numerical evaluation of the steady state was performed for up to 36 qubits. The huge size of the state space in our analysis is dealt with by exploiting a symmetry in the master equation that reduces the scaling of computer resources from exponential to polynomial. Based on these results we estimate that an error-free solution can be retrieved from the steady state after $O\left({\log }_2{\log }_{2}N\right)$ repetitions, with near-unit probability. This brings the overall scaling to $O\left(\sqrt{N}{\log }_2{\log }_{2}N\right)$, only slightly worse than for the ideal quantum case.

The irreversible time evolution of a quantum system interacting with a large environmental system can be described by a quantum master equation. When an external field is applied to a quantum system, a non-Markovian mater equation is derived in a rigorous way, where the relaxation terms in the quantum master equation include the effects of the external field. It is shown that, when the external field is a sequence of phase-modulation pulses, the decoherence of the quantum system can be suppressed under certain conditions. To see the effects of phase-modulation pulses, the irreversible time evolutions of qubit and photon systems are investigated in detail.

We present a systematic experimental study of the absorption and fluorescence spectra of the $6S_{1∕2}\text{−}6P_{1∕2}$ transition in Cs atoms isolated in solid ${}^4\mathrm{He}$ matrices. The bubble model developed earlier for alkali-metal atoms in liquid He is revised and applied to the present system. The analysis of the dependencies of absorption and fluorescence wavelengths on He pressure in liquid and solid He (cubic and hexagonal) environments leads us to modify the bubble model by taking the elastic deformation of solid He by the atomic bubble into account.

Electron-impact ionization and recombination cross sections and rate coefficients are calculated for $M$-shell Ar atomic ions using a configuration-average distorted-wave method. The electron-impact ionization calculations are for all atomic ions in the Ar isonuclear sequence. Ionization contributions include both direct ionization and excitation-autoionization processes. Good agreement is found between theory and experimental crossed-beam measurements for moderately charged ion stages. Comparisons are made with previous theoretical calculations where possible. We also generate rate coefficients for neutral argon ionization, based on recent $R$-matrix with pseudostates calculations. Electron-impact dielectronic recombination is calculated for all $M$-shell ions of argon. For ${\mathrm{Ar}}^{6+}$ and ${\mathrm{Ar}}^{7+}$ the current theoretical results agree well with previous level-resolved distorted-wave calculations. In order to compare with published ionization balance results our dielectronic recombination data are combined with literature values for the higher ion stages and with recent radiative recombination data for all the ion stages. We find significant differences in our equilibrium fractional abundances for the $M$-shell ions, compared with literature values. We relate these differences to the underlying atomic data.

We deal with the effects of an anharmonic trap on an interacting two-boson system in one dimension. Our primary focus is on the role of the induced coupling between the center of mass and the relative motion as both anharmonicity and the (repulsive) interaction strength are varied. The ground state reveals a strong localization in the relative coordinate, counteracting the tendency to fragment for stronger repulsion. To explore the quantum dynamics, we study the system’s response upon (i) exciting the harmonic ground state by continuously switching on an additional anharmonicity and (ii) displacing the center of mass, this way triggering collective oscillations. The interplay between collective and internal dynamics materializes in the collapse of oscillations, which are explained in terms of few-mode models.

We investigate the performance of a selective cloning machine based on linear optical elements and Gaussian measurements, which allows one to clone at will one of the two incoming input states. This machine is a complete generalization of a $1\to 2$ cloning scheme demonstrated by Andersen et al. [Phys. Rev. Lett. 94, 240503 (2005)]. The input-output fidelity is studied for a generic Gaussian input state, and the effect of nonunit quantum efficiency is also taken into account. We show that, if the states to be cloned are squeezed states with known squeezing parameter, then the fidelity can be enhanced using a third suitable squeezed state during the final stage of the cloning process. A binary communication protocol based on the selective cloning machine is also discussed.

We use all-order relativistic many-body perturbation theory to study $5s^{2}nl$ configurations of $\mathrm{In}\mathrm{I}$ and $\mathrm{Sn}\mathrm{II}$. Energies, $E1$ amplitudes, and hyperfine constants are calculated using all-order method, which accounts for single and double excitations of the Dirac-Fock wave functions. A comprehensive review of experimental and theoretical studies of $\mathrm{In}\mathrm{I}$ and $\mathrm{Sn}\mathrm{II}$ properties is given. Our results are compared with other studies were available.

The influence of a tight isotropic harmonic trap on photoassociation of two ultracold alkali-metal atoms forming a homonuclear diatomic is investigated using realistic atomic interaction potentials. Confinement of the initial atom pair due to the trap leads to a uniform strong enhancement of the photoassociation rate to most, but also to a strongly suppressed rate for some final states. Thus tighter traps do not necessarily enhance the photoassociation rate. A further massive enhancement of the rate is found for strong interatomic interaction potentials. The details of this interaction play a minor role, except for large repulsive interactions for which a sharp window occurs in the photoassociation spectrum as is known from the trap-free case. A comparison with simplified models describing the atomic interaction like the pseudopotential approximation shows that they often provide reasonable estimates for the trap-induced enhancement of the photoassociation rate even if the predicted rates can be completely erroneous.

A general procedure for systematically evaluating the long-range dispersion interaction between two heteronuclear atoms in arbitrary states is outlined. The $C_6$ dispersion parameter can always be written in terms of sum rules involving oscillator strengths only and formulas for a number of symmetry cases are given. The dispersion coefficients for excited alkali-metal atoms interacting with the ground-state H and He are tabulated.

A mechanism for the formation of a different type of stationary state with macroscopical number of phonons in condensed atomic gases is proposed. This mechanism is based on generating longitudinal phonons as a result of parametric resonance caused by a permanent modulation of the transverse trap frequency in an elongated trap. The phonon-phonon interaction predetermines the self-consistent evolution which is completed with macroscopic population of one from all levels within the energy interval of parametric amplification. This level proves to be shifted to the edge of this interval. All other levels end the evolution with zero population.

We present an algorithmic approach to calculate the quantum-noise spectral density of photocurrents generated by optical fields with arbitrary discrete classical spectrum in coherent or squeezed states. The measurement scheme may include an arbitrary number of demodulations of the photocurrent. Thereby, our method is applicable to the general heterodyne detection scheme, which is implemented in many experiments. For some of these experiments, e.g., in laser-interferometric gravitational-wave detectors, a reliable prediction of the quantum noise of fields in coherent and squeezed states plays a decisive role in the design phase and detector characterization. Still, our investigation is limited in two ways. First, we consider only coherent and squeezed states of the field, and second, we demand that the photocurrent depends linearly on the field’s vacuum amplitudes, which means that at least one of the classical components is comparatively strong.

In this paper we study the evolution properties along with inversion phenomena of the resonance interactions of a single two-level atom with $n$-mode cavity fields. A general expression of the state for the $n$-mode field is presented. It is found that this atom-field interaction model obeys the Rabi oscillation.

We show that positivity of every partial transpose of $N$-partite quantum states implies inequalities on Bell correlations which are stronger than standard Bell inequalities by a factor of $2^{(N-1)∕2}$. A violation of the inequality implies that the system is in a bipartite distillable entangled state. It turns out that a family of $N$-qubit bound entangled states proposed by Dür [Phys. Rev. Lett. 87, 230402 (2001)] violates the inequality for $N⩾4$.

In the light of recent experimental results of Jung et al. [Phys. Rev. A 75, 052707 (2007)], we have carried out relativistic distorted wave calculations for electron impact excitation of the ten higher-lying fine-structure levels of the $3p^5$ $5p$ configuration of argon from the lowest metastable states (the $J=0,2$ levels of the $3p^5$ $4s$ configuration). We compare our theoretical results with their experimental results and discuss the differences from the similar excitation to the $3p^5$ $4s$ levels from the same metastable states.

High-order harmonic generation from asymmetric molecules is investigated, and the concept of phase-stabilized infrared ultrashort laser pulses is extended to the extreme ultraviolet regime. It is shown that the ionization symmetry in consecutive half optical cycles is broken for asymmetric molecules, and both even and odd harmonics with comparable intensity are produced. In the time domain, only one attosecond pulse is generated in each cycle of the driving field, and the carrier-envelope phases of the attosecond pulses are equal. Consequently, a clean attosecond pulse train with the same carrier-envelope phase from pulse to pulse is obtained in the extreme ultraviolet regime.

We study measurement-based quantum computation (MQC) using as a quantum resource the planar code state on a two-dimensional square lattice (planar analog of the toric code). It is shown that MQC with the planar code state can be efficiently simulated on a classical computer if at each step of MQC the sets of measured and unmeasured qubits correspond to connected subsets of the lattice. The simulation scheme is built upon Barahona’s algorithm for computing the partition function of the Ising model on a planar graph. Our results provide a simulation method for MQC centered around planarity of graphs.

A detailed large-scale calculation on the resonant excitation rate coefficients from the ground state to the 106 fine-structure levels belonging to $3l^{17}4l^{\prime }$ ($l=0,1,2$; $l^{\prime }=0,1,2,3$) configurations of Ni-like tantalum have been performed using the relativistic distorted-wave approximation. The contributions through all possible Cu-like doubly excited states $3l^{17}4l^{\prime }{n}^{″}{l}^{″}$ and $3l^{17}5l^{\prime }{n}^{″}{l}^{″}$ ($n^{″}⩽15$, $l^{″}⩽8$) are calculated. The validity of $n^{″-3}$ scaling law is investigated. The radiative damping effects on resonant excitation rates are studied. The significant effects arising from decays to autoionizing levels are also investigated. The contributions from resonant excitation are found to be as important as direct excitation processes for most transitions. In some cases, the resonant excitation can enhance the excitation rate coefficients by an order of magnitude. Large discrepancies between the present resonant excitation rate coefficients with previously published values are found, and the present results should be more reliable and accurate.

We present a scalable solid-state system in which the superconducting charge qubits are coupled with a nanomechanical resonator (NAMR) to achieve highly entangled cluster states, which are responsible for one-way quantum computing via single-qubit measurements. Since the NAMR can play the essential role of the data bus, the long-range interactions among the qubits can occur. Therefore, without using the interacting picture we can directly obtain the long-range Ising-like unitary operator $U_z\left(\lambda \right)=\exp \left[i\lambda S_z^2\right]$ with $S_z$ the collective spin operator in $z$ direction and $\lambda$ a parameter, which is insensitive to the thermal state of the NAMR. Based on this unitary operator, a set of highly entangled cluster states can be produced by efficient one-step generation. Moreover, the robustness of the highly entangled cluster states with respect to unavoidable parameter variations is also demonstrated.