We present a theoretical quasiclassical treatment of the formation, during Coulomb explosion, of highly excited neutral H atoms (${\text{H}}^{*}$) for strongly driven ${\text{H}}_2$. This process, where after the laser field is turned off, one electron escapes to the continuum while the other occupies a Rydberg state, was recently reported in an experimental study [B. Manschwetus et al., Phys. Rev. Lett. 102, 113002 (2009)]. We find that two-electron effects are important in order to correctly account for all pathways leading to ${\text{H}}^{*}$ formation. We identify two pathways where the electron that escapes to the continuum does so either very quickly or after remaining bound for a few periods of the laser field. These two pathways of H${}^{*}$ formation have distinct traces in the probability distribution of the escaping electron momentum components.

We consider the effect of atomic hydrogen exposure to a system of two undoped sheets of graphene grown near a silica surface (the first adsorbed to the surface and the second freestanding near the surface). In the absence of atomic hydrogen, the van der Waals force between the sheets is attractive at all separations, causing the sheets to come closer together. However, with the addition of atomic hydrogen between the sheets, the long-range van der Waals interaction turns repulsive at a critical concentration. The underlying triple layer structure (SiO${}_2$–atomic hydrogen gas–air) gives rise to a long-range repulsion that at large-enough separations dominates over the more rapidly decaying attraction between the two-dimensional undoped graphene sheets (and between the outer graphene sheet and SiO${}_2$). This may be an avenue to tune the separation between two graphene sheets with the gas concentration. The doping of the graphene layers increases the attractive part of the interaction and hence reduces the net repulsive interaction.

Two simple ab initio methods based on one-electron wave functions are employed to calculate the single-electron capture and single ionization of ${\mathrm{H}}_2\mathrm{O}$ and CO molecules by ion impact. The anisotropy of the molecular targets is taken into account by using multicenter pseudopotentials to represent the interaction of the active electron with the ionic molecular core. These two methods are applied to the study of three collisional systems: ${\mathrm{H}}^{+}+{\mathrm{H}}_2\mathrm{O}$, ${\mathrm{He}}^{2+}+{\mathrm{H}}_2\mathrm{O}$, and ${\mathrm{C}}^{2+}+\mathrm{CO}$. Comparison with experiments and other theoretical works is presented when available.

We study theoretically the photoabsorption spectra of an attosecond extreme ultraviolet (XUV) pulse by a laser-dressed atomic system. A weak XUV excites an autoionizing state which is strongly coupled to another autoionizing state by a laser. The theory was applied to explain two recent experiments [Loh, Greene, and Leone, Chem. Phys. 350, 7 (2008); Wang, Chini, Chen, Zhang, Cheng, He, Cheng, Wu, Thumm, and Chang, Phys. Rev. Lett. 105, 143002 (2010)] where the absorption spectra of the XUV lights were measured against the time delay between the laser and the XUV. In another example, we study an attosecond pulse exciting the $2s2p{(}^{1}P)$ resonance of helium which is resonantly coupled to the $2s^2{(}^{1}S)$ resonance by a moderately intense 540-nm laser. The relation between the photoabsorption spectra and the photoelectron spectra and the modification of the transmitted lights in such an experiment are analyzed. The role of Rabi flopping between the two autoionizing states within their lifetimes is investigated with respect to the laser intensity and detuning.

Finite size scalings of the momentum distribution and noise correlations are performed to study Mott insulator, Bose glass, and superfluid quantum phases in hard-core bosons (HCBs) subjected to quasiperiodic disorder. The exponents of the correlation functions at the superfluid to Bose-glass (SF-BG) transition are found to be approximately one half of the ones that characterize the superfluid phase. The derivatives of the peak intensities of the correlation functions with respect to quasiperiodic disorder are shown to diverge at the SF-BG critical point. This behavior does not occur in the corresponding free fermion system, which also exhibits an Anderson-like transition at the same critical point and thus provides a unique experimental tool to locate the phase transition in interacting bosonic systems. We also report on the absence of primary sublattice peaks in the momentum distribution of the superfluid phase for special fillings.

It is shown that wave-packet localization in space-periodic systems subjected to generic ac forces having equidistant zeros is a highly nonlinear phenomenon that is fully controlled by the integral of the ac force over a half period (i.e., the force's impulse), and that suitably varying this impulse allows one to achieve wave-packet localization for almost any value of the force's amplitude, in contrast to the standard case of a harmonic force. In particular, the result is demonstrated in two simple universal models—driven two-level systems in the limit of small periods, and periodically curved waveguide arrays in the nearest-neighbor tight-binding approximation. Remarkably, the problem motivated the introduction of a nonlinear generalization of the zeroth-order Bessel function $J_0\left(z\right)$.

We consider the emission pattern of a three-dimensional pointlike dipole situated near a left-handed-medium slab. Unlike earlier work, we focus on the direction normal to the slab surface. It is shown that the evanescent field may help to narrow the major peak of the image created by the propagating field. We point out that care has to be taken when applying Snell's law to the superlens problem. In particular, it cannot explain why the focus is shifted away from the ideal position when material absorption decreases below some threshold value.

Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. [Nature (London) 454, 07610 (2009)]. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation-driven repulsion sets in at around 3 nm. To our knowledge, retardation effects have never been found at such a small distance before. Retardation effects are usually associated with large distances.

Using analytical and numerical methods, it is shown that the momentum distribution of a matter wave packet launched in a random potential exhibits a pronounced coherent backscattering (CBS) peak. By analyzing the momentum distribution, key transport times can be directly measured. The CBS peak can be used to prove that transport occurs in the phase-coherent regime, and measuring its time dependence permits monitoring the transition from classical diffusion to Anderson localization.

The limitation on the shareability of quantum entanglement over several parties, the so-called monogamy of entanglement, is an issue that has received considerable attention from the quantum information community over the last decade. A natural question of interest in this connection is whether monogamy of correlations is true for correlations other than entanglement. This issue is examined here by choosing quantum deficit, proposed by A. K. Rajagopal and R. W. Rendell [Phys. Rev. A 66, 022104 (2002)], an operational measure of correlations. In addition to establishing the polygamous nature of the class of three-qubit symmetric pure states characterized by two distinct Majorana spinors (to which the $W$ states belong), those with three distinct Majorana spinors [to which Greenberger-Horne-Zeilinger (GHZ) states belong] are shown to either obey or violate monogamy relations. While the generalized $W$ states can be monogamous or polygamous, the generalized GHZ states exhibit monogamy with respect to quantum deficit. The issue of using monogamy conditions based on quantum deficit to witness the states belonging to stochastic local operations and classical communication (SLOCC) inequivalent classes is discussed in light of these results.

We present a scheme of control for the arbitrary optical interface mediated by a nanoscale mechanical oscillator between flying qubits and optical nonactive solid-state qubits. This quantum interface lays the foundation for many key functions of a quantum network, such as transferring, swapping, and entangling qubits between distant nodes of a quantum network. Numerical simulations of the quantum interface operations show high fidelities and robust tolerance under realistic experimental conditions. Compared with a previous scheme [K. Stannigel et al., Phys. Rev. Lett. 105, 220501 (2010)], it may significantly increase the speed of state transfer operation of high fidelity.

Suppose Alice and Bob have access to two separated regions, respectively, of a system of electrons moving in the presence of a regular one-dimensional lattice of binding atoms. We consider the problem of communicating as much quantum information, as measured by the qubit rate, through this quantum-information wire as possible. We describe a protocol whereby Alice and Bob can achieve a qubit rate for these systems which is proportional to $N^{-\frac{1}{3}}$ qubits per unit time, where $N$ is the number of lattice sites. Our protocol also functions equally in the presence of interactions modeled via the $t-J$ and Hubbard models.

I propose a practical scheme of hyperconcentration, by which two-qubit photon spin and two-qudit orbital angular momentum (OAM) maximally entangled states can be distilled simultaneously. The original nonmaximally hyperentangled photon pairs are generated by parametric down conversion and the symmetrical procrustean concentration is then performed using pairs of spatial light modulators (operating on OAM) and partial polarizing interferometers (operating on spin). Furthermore, I show that a generalized Shannon dimensionality can be introduced to evaluate the performance, which is maximized with the formation of a comblike entangled spectrum for composite spin-orbit modes. The results hold promise for ultrahigh-dimensional quantum-information processing.

We have investigated the ultrafast electronic relaxation of Au${}_7^{-}$ using time-resolved photoelectron spectroscopy combined with first-principles simulations of the excited-state dynamics. Unlike previous findings, which have demonstrated molecularlike excited-state relaxation in Au${}_7^{-}$ at low excitation energy (1.56 eV), we show here that excitation with 3.12 eV leads to bulklike electronic relaxation without a considerable change of geometry. The experimental findings are fully supported by theoretical simulations, which reveal a bulklike electron-hole relaxation mechanism in a far band-gap cluster. Our findings demonstrate that small gold clusters in the sub-nm size range can exhibit either molecularlike or bulklike properties, depending on the excitation energy.

We perform time-dependent calculations of single-photon two-electron ionization of the aligned H${}_2$ molecule by an xuv pulse. Solution of the time-dependent Schrödinger equation is sought in spherical coordinates on a radial grid by time propagation using the Arnoldi-Lanczos method. From these calculations, we derive the total integrated as well as fully differential ionization cross sections for equal energy sharing and various orientations of the internuclear axis relative to the polarization vector of light. Satisfactory agreement with available literature data validates the present theoretical model. We supplement our numerical computations with an amplitude analysis of differential cross sections using the atomiclike formalism of Feagin [J. Phys. B 31, L729 (1998)]. This analysis provides some additional insight into mechanisms of double photoionization of the aligned H${}_2$ molecule.

We decelerated an atomic beam of ${}^{87}$Rb using a stimulated-emission slowing technique that employs a bichromatic standing light wave of high intensity, and increased the atom number in a magneto-optical trap (MOT) of low capture velocity by up to a factor of 14, and the load rate into the MOT by a factor of 20. We performed the slowing over distances under 1.5 cm with 5.2 mW of total power in the bichromatic beams. The average stimulated force was 2.2 times the maximum spontaneous emission force, and could be made even stronger in a smaller apparatus.

It is shown that, in a reasonable approximation, the quantum state of $p$ bosons in a bipartite square two-dimensional optical lattice is governed by the nonlinear boson model describing tunneling of boson pairs between two orthogonal degenerate quasimomenta on the edge of the first Brillouin zone. The interplay between the lattice anisotropy and the atomic interactions leads to the second-order phase transition between the number-squeezed and coherent phase states of the $p$ bosons. In the isotropic case of the recent experiment [G. Wirth, M. Ölschläger, and A. Hemmerich, Nat. Phys. 7, 147 (2011)], the $p$ bosons are in the coherent phase state, where the relative global phase between the two quasimomenta is defined only up to mod($\pi$): $\phi =\pm \pi /2$. The quantum phase diagram of the nonlinear boson model is given.

Repulsively bound pairs of particles in a lattice governed by the Bose-Hubbard model can form stable incompressible clusters of dimers corresponding to finite-size $n=2$ Mott insulators. Here we study the dynamics of hole defects in such clusters corresponding to unpaired particles which can resonantly tunnel out of the cluster into the lattice vacuum. Due to bosonic statistics, the unpaired particles have different effective mass inside and outside the cluster, and “evaporation” of hole defects from the cluster boundaries is possible only when their quasimomenta are within a certain transmission range. We show that quasithermalization of hole defects occurs in the presence of catalyzing particle defects which thereby purify the Mott-insulating clusters. We study the dynamics of a one-dimensional system using analytical techniques and numerically exact time-dependent density-matix renormalization-group simulations. We derive an effective strong-interaction model that enables simulations of the system dynamics for much longer times. We also discuss a more general case of two bosonic species which reduces to the fermionic Hubbard model in the strong interaction limit.

We first analytically examine the occurrence of modulational instability in all phases of $F=2$ spinor homogeneous condensate from the possible stationary solutions. Then we numerically show the similar results by extending our analysis to trapped condensates (inhomogeneous). From both analyses we conclude that modulation instability depends on the relative phase between the components and initial population for the polar phase. We also observe spin-mixing dynamics during evolution of the spinor condensate.

The long-standing question of finding the momentum representation for the $s$-wave zero-range interaction in three spatial dimensions is here solved. This is done by expressing a certain distribution, introduced in a formal way in [S. Tan, Ann. Phys. (NY) 323, 2952 (2008)], explicitly. The resulting form of the Fourier-transformed pseudopotential remains very simple. Operator forms for the so-called Tan's selectors, which, together with Fermi-Huang pseudopotential, largely simplify the derivation of Tan's universal relations for the Fermi gas, are here derived and are also very simple. A momentum cutoff version of the pseudopotential is also provided, and with this no apparent contradiction to the notion of integrals in Tan's methods is left. The equivalence, even at the intermediate-step level, between the pseudopotential approach and momentum-space renormalization of the bare Dirac delta interaction is then shown by using the explicit form of the cutoff pseudopotential.