The spin angular momentum accumulates in the Cs nuclei of salt on contact with optically pumped Cs vapor. The spin polarization in stable chloride as well as dissociative hydride indicates that nuclear dipole interaction works in spin transferring with a lesser role of atom exchange. In the solid film, not only the spin buildup but also the decay of enhanced polarization is faster than the thermal recovery rate for the bulk salt. Eliminating the signal of thick salt, we find that the nuclear spin polarization in the chloride film reaches over 100 times the thermal equilibrium.

The covariant quantization of the electromagnetic field in the Lorentz gauge gives rise to longitudinal and scalar photons in addition to the usual transverse photons. It is shown here that the exchange of longitudinal and scalar photons can produce entanglement between two distant atoms or harmonic oscillators. The form of the entangled states produced in this way is very different from that obtained in the Coulomb gauge, where the longitudinal and scalar photons do not exist. A generalized gauge transformation is used to show that all physically observable effects are the same in the two gauges, despite the differences in the form of the entangled states. An approach of this kind may be useful for a covariant description of the dynamics of quantum information processing.

We present a set of two-dimensional aperiodic structures with a large complete photonic band gap (PBG), which are named two-pattern photonic crystals. By superposing two substructures without regard to registration, we designed six new aperiodic PBG structures having a complete PBG larger than 15% for ${\varepsilon }_2/\phantom{{\varepsilon }_2{\varepsilon }_1}{\varepsilon }_1=11.4$. The rod-honeycomb two-pattern photonic crystal provides the largest complete PBG to date. An aperiodic structure becomes the champion structure with the largest PBG. Surprisingly, the TM and TE gaps of a two-pattern photonic crystal are much less interdependent than the PBGs of conventional photonic crystals proposed before, affording interesting capabilities for us to tune the TM and TE PBGs separately. By altering the respective substructures, optical devices for different polarizations (TE, TM, or both) can readily be designed.

This Rapid Communication presents a fast-kick-off search algorithm for quickly finding optimal control fields in the state-to-state transition probability control problems, especially those with poorly chosen initial control fields. The algorithm is based on a recently formulated monotonically convergent scheme [T.-S. Ho and H. Rabitz, Phys. Rev. E 82, 026703 (2010)]. Specifically, the local temporal refinement of the control field at each iteration is weighted by a fractional inverse power of the instantaneous overlap of the backward-propagating wave function, associated with the target state and the control field from the previous iteration, and the forward-propagating wave function, associated with the initial state and the concurrently refining control field. Extensive numerical simulations for controls of vibrational transitions and ultrafast electron tunneling show that the new algorithm not only greatly improves the search efficiency but also is able to attain good monotonic convergence quality when further frequency constraints are required. The algorithm is particularly effective when the corresponding control dynamics involves a large number of energy levels or ultrashort control pulses.

The energy spectra of electrons ejected in ${\mathrm{He}}^{2+}-\mathrm{He}$ collisions were measured in the ion energy range 6–30 keV. Theoretical analysis of the ionization mechanisms has been performed on the basis of the advanced adiabatic approximation for one-electron processes and perturbation theory for two-electron processes. The ionization channel 2$p$σ${}^2$ → 1$s$σ$\mathit{nd}$σ → 1$s$σε$d$σ has been revealed, which makes a considerable contribution to the ionization cross section in the keV ion energy range.

By utilizing giant Kerr nonlinearity obtained by electromagnetically induced transparency (EIT), tunable volume transmission holographic gratings for a weak probe field can be generated by means of a standing-wave signal field at low light levels in a four-level $N$-type ultracold atomic ensemble. The induced grating can be characterized as a mixed volume holographic grating with a strong phase modulation accompanied by a weak amplitude modulation. Based on Kogelnik's coupled-wave theory in optical holography, we find that high diffraction efficiency (up to $85\%$) and sensitive angular selectivity (up to $\pm 0.000149$ rad) can be achieved for the induced grating in the Bragg diffraction regime. And, both of them can be dynamically controlled by tuning the weak standing-wave signal field and the coupling field. Our study not only develops a fundamental understanding of volume diffraction effects in EIT media, but also provides a practical prototype of EIT-based holographic devices for all-optical classical and quantum information processing.

We analytically explore a wide class of optical similariton solutions to the nonlinear Schrödinger equation appropriately modified to model beam propagation in a tapered, graded-index nonlinear-fiber amplifier with an external source. Under certain physical conditions, we reduce the coupled nonlinear Schrödinger equations to a single-wave equation that aptly describes similariton propagation through asymmetric twin-core fiber amplifiers. The asymmetric twin-core fiber is composed of two adjoining, closely spaced, single-mode fibers in which the active one is a tapered, graded-index nonlinear-fiber and the passive one is a step-index fiber. We obtain these self-similar waves for different choices of tapered index profile, using a Möbius transformation. Our procedure is applicable for both self-focusing and self-defocusing nonlinearities.

We study, in time domain, the exchange of momentum between an electromagnetic pulse and a three-dimensional, discrete, spherical invisibility cloak. We find that a discrete cloak, initially at rest, would experience an electromagnetic force due to the pulse but would acquire zero net momentum and net displacement. On the other hand, we find that while the cloak may manage to conceal an object and shroud it from the electromagnetic forces associated with the pulse, the cloak itself can experience optomechanical stress on a scale much larger than the object would in the absence of the cloak. We also consider the effects of material dispersion and losses on the electromagnetic forces experienced by the cloak and show that they lead to a transfer of momentum from the pulse to the cloak.

All of the $\mathcal{P}\mathcal{T}$-symmetric potentials that have been studied so far have been local. In this paper, nonlocal $\mathcal{P}\mathcal{T}$-symmetric separable potentials of the form $V(x,y)=i\epsilon \left[U\right(x\left)U\right(y)-U(-x\left)U\right(-y\left)\right]$, where $U\left(x\right)$ is real, are examined. Two specific models are examined. In each case, it is shown that there is a parametric region of the coupling strength $\epsilon$ for which the $\mathcal{P}\mathcal{T}$ symmetry of the Hamiltonian is unbroken and the bound-state energies are real. The critical values of $\epsilon$ that bound this region are calculated.

We present and demonstrate a method for optical homodyne tomography based on the inverse Radon transform. Different from the usual filtered back-projection algorithm, this method uses an appropriate polynomial series to expand the Wigner function and the marginal distribution, and discretize Fourier space. We show that this technique solves most technical difficulties encountered with kernel deconvolution-based methods and reconstructs overall better and smoother Wigner functions. We also give estimators of the reconstruction errors for both methods and show improvement in noise handling properties and resilience to statistical errors.

We propose and theoretically study a method for the stochastic realization of arbitrary quantum channels on multimode single-photon qudits. In order for our method to be undemanding in its implementation, we restrict our analysis to linear-optical techniques, vacuum ancillary states, and nonadaptive schemes, but we allow for random switching between different optical networks. With our method it is possible to deterministically implement random-unitary channels and to stochastically implement general channels. We provide an expression for the optimal probability of success of our scheme and calculate this quantity for specific examples such as the qubit amplitude-damping channel. The success probability is shown to be related to the entanglement properties of the Choi-Jamiołkowski state isomorphic to the channel.

We introduce a quantity which is formed using classical notions of mutual information and which is computed using the results of projective measurements. This quantity constitutes a sufficient condition for entanglement and represents the amount of information that can be extracted from a bipartite system for spacelike separated observers. In addition to discussion, we provide simulations as well as experimental results for the singlet and maximally correlated mixed states.

Entanglements within qubits are studied for the subspace of definite particle states or definite number of up spins. A transition from an algebraic decay of entanglement within two qubits with the total number $N$ of qubits to an exponential one when the number of particles is increased from two to three is studied in detail. In particular the probability that the concurrence is nonzero is calculated using statistical methods and is shown to agree with numerical simulations. Further entanglement within a block of $m$ qubits is studied using the log-negativity measure, which indicates that a transition from algebraic to exponential decay occurs when the number of particles exceeds $m$. Several algebraic exponents for the decay of the log negativity are analytically calculated. The transition is shown to be possibly connected to the changes in the density of states of the reduced density matrix, which has a divergence at the zero eigenvalue when the entanglement decays algebraically.

For potentials with attractive tails, as occur in typical atomic interactions, we present a simple formula for the $s$-wave phase shift ${\delta }_0$. It exposes a universal dependence of ${\delta }_0\left(E\right)$ on the potential tail and the influence of effects specific to a given potential, which enter via the scattering length $a$, or equivalently, the noninteger part ${\Delta }_{\mathrm{th}}$ of the threshold quantum number $n_{\mathrm{th}}$. The formula accurately reproduces ${\delta }_0\left(E\right)$ from threshold up to the semiclassical regime, far beyond the validity of the effective-range expansion. We derive the tail functions occurring in the formula for ${\delta }_0\left(E\right)$ and demonstrate the validity of the formula for attractive potential tails proportional to $1/r^6$ or to $1/r^4$, and also for a mixed potential tail consisting of a $1/r^4$ term together with a non-negligible $1/r^6$ contribution.

We study two-body dipolar scattering in two dimensions with a tilted polarization axis. This tilt reintroduces the anisotropic interaction in a controllable manner. As a function of this polarization angle, we present the scattering rates in both the threshold and semiclassical regimes. Additionally, we study the properties of the molecular bound states as a function of the polarization angle.

A fully relativistic calculation of the double photoionization of heliumlike atoms is presented. The approach is based on the partial-wave representation of the Dirac continuum states and accounts for the retardation in the electron-electron interaction as well as the higher-order multipoles of the absorbed photon. The electron-electron interaction is taken into account to the leading order of the perturbation theory. The relativistic effects are shown to become prominent already for the medium-$Z$ ions, changing the shape and the asymptotic behavior of the photon energy dependence of the ratio of the double-to-single photoionization cross section.

Double-differential ionization cross sections of adenine (${\mathrm{C}}_5{\mathrm{H}}_5{\mathrm{N}}_5$) by 1.0-MeV protons have been measured using a vapor-phase adenine target. Ejected electrons were analyzed by a ${45}^{\circ }$ parallel-plate electrostatic spectrometer in an electron energy range from 1 to 1000 eV at electron emission angles from ${15}^{\circ }$ to ${165}^{\circ }$. The effective target thickness of adenine was determined by a Rutherford forward scattering method and a vapor deposition method. Present data are in good agreement with recent calculations. Comparisons were made with other data on various hydrocarbon molecules. It was found that the ionization cross sections of these molecules can be scaled fairly well in terms of the total number of valence electrons.

Fragmentation branching ratios for channels involving H${}^{+}$ emission and associated kinetic energy release of the H${}^{+}$ fragment [KER(H${}^{+}$)] have been measured for multicharged C${}_n$H${}^q$${}^{+}$ molecules produced in high velocity (3.6 a.u.) collisions between C${}_n$H${}^{+}$ projectiles and helium atoms. For CH${}^q$${}^{+}$ ($q$ ≤ 4) molecules, measured KER(H${}^{+}$) were found well below predictions of the simple point charge Coulomb model (PCCM) for all $q$ values. Multireference configuration interaction (MRCI) calculations for ground as well as electronic excited states were performed which allowed a perfect interpretation of the CH${}^q$${}^{+}$ experimental results for low charges ($q$ = 2–3) as well as for the highest charge ($q$ $=$ 4). In this last case we could show, on the basis of ionization cross sections calculations and experimental measurements performed on the same systems at slightly higher velocity (4.5 a.u.), the prominent role played by inner-shell ionization followed by Auger relaxation and could extract the lifetime of this Auger relaxation giving rise to the best agreement between the experiment and the calculations. For dissociation of C${}_2$H${}^q$${}^{+}$ and C${}_3$H${}^q$${}^{+}$ with the highest charges ($q$ ≥ 5), inner-shell ionization contributed in a prominent way to the ion production. In these two cases it was shown that measured KER(H${}^{+}$) were in good agreement with PCCM predictions when those were corrected for Auger relaxation with the same Auger lifetime value as in CH${}^{3+}$.

We have excited helium atoms from their metastable 2 ${}^{3}S$ state to Rydberg states in the range $13<n<50$ in a two-step process via the 3 ${}^{3}P$ state using light at $\lambda =389$ nm and 785–815 nm. Atoms in a thermal beam (100 K) cross partially overlapping laser beams of the appropriate frequencies in the counterintuitive order to exploit the high efficiency of stimulated rapid adiabatic passage. The interaction region is between two plates that can be used for Stark tuning in a few V/cm field or for field ionization. At fields much too low for field ionization, we observe signals attributed to ionization by blackbody radiation. Multiple tests confirm this attribution as the cause of ionization. For example, by heating the plates we observe the expected signal increases. Our experiments reinforce previous work where the interaction between Rydberg atoms and room temperature blackbody radiation is important for experiments.

Triple-differential cross sections for two-photon double ionization of the aligned hydrogen molecule at the equilibrium distance are presented for a central photon energy of 30 eV. The temporal response of the laser-driven molecule is investigated by solving the time-dependent Schrödinger equation in full dimensionality using two-center elliptical coordinates and a finite-element discrete-variable-representation approach. The molecular orientation is found to have a strong effect on the emission modes of the two correlated photoelectrons. This molecular effect is most noticeable when the molecular axis and the laser polarization vector are oriented parallel to each other. For intermediate cases between the parallel and perpendicular geometries, the dominant emission modes for two-electron ejection oscillate between those for the two extreme cases. The contributions from different ionization channels are also analyzed in detail. Depending on the emission direction of the reference electron, the interference contributions from the various channels can be constructive or destructive at small alignment angles, while they always contribute constructively to the triple-differential cross sections near the perpendicular geometry.