We study Mie scattering of Laguerre-Gaussian (LG) light beams remodelled using the method of far-field matching. The theoretical results are used to analyze the optical field in the near-field region for purely azimuthal LG beams characterized by a nonzero azimuthal mode number $m_{\mathrm{LG}}$. The morphology of photonic nanojets and the near-field structure of optical vortices associated with the components of the electric field are both found to be highly sensitive to the mode number $m_{\mathrm{LG}}$.

In a circuit quantum eletrodynamic system, a chain of $N$ qubits inhomogeneously coupled to a cavity field forms a mesoscopic quasilattice, which is characterized by its degree of deformation from a normal lattice. This deformation is a function of the relative spacing, that is the ratio of the qubit spacing to the cavity wavelength. A polariton mode arises in the quasilattice as the dressed mode of the lattice excitation by the cavity photon. We show that the transition probability of the polariton mode is either enhanced or decreased compared to that of a single qubit by the deformation, giving a selective spontaneous radiation spectrum. Further, unlike a microscopic lattice with large-$N$ limit and nearly zero relative spacing, the polariton in the quasilattice has uneven decay rate over the relative spacing. We show that this unevenness coincides with the cooperative emission effect expected from the superradiance model, where alternative excitations in the qubits of the lattice result in maximum decay.

The Kochen-Specker (KS) theorem is a central result in quantum theory and has applications in quantum information. Its proof requires several yes-no tests that can be grouped in contexts or subsets of jointly measurable tests. Arguably, the best measure of simplicity of a KS set is the number of contexts. The smaller this number is, the smaller the number of experiments needed to reveal the conflict between quantum theory and noncontextual theories and to get a quantum vs classical outperformance. The original KS set had 132 contexts. Here we introduce a KS set with seven contexts and prove that this is the simplest KS set that admits a symmetric parity proof.

We extend a general conformal mapping approach to complex space transformations and apply it to design optical elements that possess loss and gain. We describe the methodology for tailoring the transformation optical media and analyze a ground-plane cloak as an example. We believe that our approach can be employed for the design of various optical and plasmonic devices and the potential impact can be significant in other fields.

We have studied stationary and quasistationary signal light pulses in cold Λ-type atomic media driven by counterpropagating control laser fields at the condition of electromagnetically induced transparency. By deriving a dispersion relation we present spectral and temporal properties of the signal light pulse and a significant influence of atomic decoherence on the coupled stationary light pulses for spatial splitting. Finally we discuss quasistationary light pulse evolution characterized by frozen spatial spreading for a robust coherent control of slow light pulses.

In this Brief Report we discuss a solution of the free-particle Schrödinger equation in which the time and space dependence are not separable. The wave function is written as a product of exponential terms, Hermite polynomials, and a phase. The peaks in the wave function decelerate and then accelerate around $t=0$. We analyze this behavior within both a quantum and a semiclassical regime. We show that the acceleration does not represent true acceleration of the particle but can be related to the envelope function of the allowed classical paths. Comparison with other “accelerating” wave functions is also made. The analysis provides considerable insight into the meaning of the quantum wave function.

The parity (P) and time-reversal (T) odd coupling constant associated with the tensor-pseudotensor (T-PT) electron-nucleus interaction and the nuclear Schiff moment (NSM) have been determined by combining the result of the measurement of the electric dipole moment (EDM) of a ${}^{129}\mathrm{Xe}$ atom and our calculations based on the relativistic-coupled-cluster (RCC) theory. Calculations using various relativistic many-body methods have been performed at different levels of approximation. The accuracies of our results are estimated by comparing our dipole polarizability calculations of the ground state of Xe with its most precise available experimental data, and taking into consideration the difference of the results of our RCC single- and double-excitation calculations with and without the important triple excitations as well as the size of our basis set. The nonlinear terms that arise in the RCC theory were found to be crucial for achieving high accuracy in the calculations. We obtain the upper limits for the T-PT electron-nucleus coupling coefficient and NSM as $1.6\times {10}^{-6}$ and $1.2\times {10}^{-9}e{\text{fm}}^3$, respectively, by combining our calculations with the available measurement. Our results, in combination with future EDM measurements in atomic Xe, could improve these limits further.

Population transfer between two valence states of the Li atom with a Raman process via intermediate autoionizing states well above the ionization threshold is investigated using a recently developed implementation of the muticonfiguration time-dependent Hartree Fock method. It is found that a properly chosen sequence of pump and Stokes $\pi$ pulses can yield a population transfer efficiency of $53\%$ at relatively low intensities, while the extension of the stimulated Raman adiabatic passage (STIRAP) approach to the XUV in this case is far less efficient and loses its characteristic robustness at high intensities. A rule of thumb for when STIRAP is practical is given, suggesting that at still shorter wavelengths STIRAP may be possible.

We derive explicit expressions for the quantum Fisher information and the symmetric logarithmic derivative (SLD) of a quantum state in the exponential form $\rho =exp\left(G\right)$; the SLD is expressed in terms of the generator $G$. Applications include quantum-metrology problems with Gaussian states and general thermal states. Specifically, we give the SLD for a Gaussian state in two forms, in terms of its generator and its moments; the Fisher information is also calculated for both forms. Special cases are discussed, including pure, degenerate, and very noisy Gaussian states.

Adjusting a previously developed Grotch-type approach to a perturbative calculation of the electronic vacuum-polarization effects in muonic atoms, we find here the two-loop vacuum-polarization relativistic recoil correction of order ${\alpha }^2{\left(Z\alpha \right)}^4{m}^2/M$ in light muonic atoms. The result is in perfect agreement with the one previously obtained within the Breit-type approach. We also discuss here simple approximations of the irreducible part of the two-loop vacuum-polarization dispersion density, which are applied to test our calculations and could be useful for other evaluations with an uncertainty better than 1%.

We investigate secret key rates for the quantum repeater using encoding [L. Jiang et al., Phys. Rev. A 79, 032325 (2009)] and compare them to the standard repeater scheme by Briegel, Dür, Cirac, and Zoller. The former scheme has the advantage of a minimal consumption of classical communication. We analyze the trade-off in the secret key rate between the communication time and the required resources. For this purpose we introduce an error model for the repeater using encoding which allows for input Bell states with a fidelity smaller than one, in contrast to the model given by L. Jiang et al. [Phys. Rev. A 79, 032325 (2009)]. We show that one can correct additional errors in the encoded connection procedure of this repeater and develop a suitable decoding algorithm. Furthermore, we derive the rate of producing entangled pairs for the quantum repeater using encoding and give the minimal parameter values (gate quality and initial fidelity) for establishing a nonzero secret key. We find that the generic quantum repeater is optimal regarding the secret key rate per memory per second and show that the encoded quantum repeater using the simple three-qubit repetition code can even have an advantage with respect to the resources compared to other recent quantum repeater schemes with encoding.

Typically two particles (spins) could be maximally entangled at zero temperature, and for a certain temperature the phenomenon of entanglement vanishes at the threshold temperature. For the Heisenberg coupled model or even the Ising model with a transverse magnetic field, one can observe some rise of entanglement even for a disentangled region at zero temperature. So we can understand this emergence of entanglement at finite temperature as being due to the mixing of some maximally entangled states with some other untangled states. Here, we present a simple one-dimensional Ising model with alternating Ising and Heisenberg spins in an arbitrarily oriented magnetic field, which can be mapped onto the classical Ising model with a magnetic field. This model does not show any evidence of entanglement at zero temperature, but surprisingly at finite temperature rise a pairwise thermal entanglement between two untangled spins at zero temperature when an arbitrarily oriented magnetic field is applied. This effect is a purely magnetic field, and the temperature dependence, as soon as the temperature increases, causes a small increase in concurrence, achieving its maximum at around 0.1. Even for long-range entanglement, a weak concurrence still survives. There are also some real materials that could serve as candidates that would exhibit this effect, such as Dy(NO${}_3$)(DMSO)${}_2$Cu(opba)(DMSO)${}_2$ [DMSO = dimethyl sulfoxide; opba = $o$-phenylenebis(oxamoto)] [J. Strečka, M. Hagiwara, Y. Han, T. Kida, Z. Honda, and M. Ikeda, Condens. Matter Phys. 15, 43002 (2012)].

It is shown that the direction of the photoelectron recoil momentum transferred to the photoion influences molecular photoionization dynamics, resulting in the appearance of a specific mode–channel interdependence. We disclose the interdependence and the interplay of the core-hole- and photoelectron-induced recoil effects by passing to normal mass-dependent modes in both coordinate and momentum spaces. As an example, the vibrational structure of the $1s^{-1}$ photoelectron line of $\text{C}{\text{O}}_2$ is investigated in detail. The intensity of bending and symmetric and asymmetric stretching vibrational and rotational excitations is found to differ substantially in the $\Sigma \to \Sigma$ and $\Sigma \to \Pi$ photoionization channels.

By considering a cylindrically symmetric generalization of a plane wave, the first-order Born approximation of screened Coulomb scattering unfolds two new dimensions in the scattering problem: transverse momentum and orbital angular momentum of the incoming beam. In this paper, the elastic Coulomb scattering amplitude is calculated analytically for incoming Bessel beams. This reveals novel features occurring for wide-angle scattering and quantitative insights for small-angle vortex scattering. The result successfully generalizes the well-known Rutherford formula, incorporating transverse and orbital angular momentum into the formalism.

Magnetic Feshbach resonances play a central role in experimental research on atomic gases at ultracold temperatures, as they allow one to control the microscopic interactions between ultracold atoms by tuning an applied magnetic field. These resonances arise due to strong hyperfine interactions between the unpaired electron and the nuclear magnetic moment of the alkali metal atoms. A major thrust of current research is to create an ultracold gas of diatomic alkali metal molecules in the ground rovibrational state of the ground electronic ${}^1\Sigma$ state. Unlike alkali metal atoms, ${}^1\Sigma$ diatomic molecules have no unpaired electrons. However, the hyperfine interactions of molecules may give rise to magnetic Feshbach resonances. We use quantum scattering calculations to study the possible width of these resonances. Our results show that the widths of magnetic Feshbach resonances in ultracold molecule-molecule collisions for ${}^1\Sigma$ molecules may exceed 1 mG, rendering such resonances experimentally detectable. We hope that this work will stimulate the experimental search of these resonances.

We study the coherent control of quantum tunneling for dipolar bosons held in a driven triple-well potential. In the high-frequency region within the resonance case, based on the non-Floquet solutions of two dipolar bosons, the influence of dipolar interaction on tunneling is investigated analytically and numerically, in which the directed selective-tunneling of a single atom is demonstrated when the two bosons are located in the middle well initially. Further, the corresponding effect is exhibited numerically for more dipolar atoms $N>2$ and the directed tunneling of 1 or $(N-1)$ atoms occurs by adjusting the driving parameters. These results may be useful in the design of atomic devices.

We show that the analysis of the time evolution of the occupation of site and momentum modes of harmonically trapped lattice hard-core bosons, under driven dipole oscillations, allows one to determine the energy of the lowest one-particle excitations of the system in equilibrium. The analytic solution of a single particle in the absence of a lattice is used to identify which function of those time-dependent observables is best fit for the analysis, as well as to relate the dynamic response of the system to its single-particle spectrum. In the presence of the lattice and of multiple particles, a much richer and informative dynamical response is observed under the drive.

Vibrations, electromagnetic oscillations, and temperature drifts are among the main reasons for dephasing in matter-wave interferometry. Sophisticated interferometry experiments, e.g., with ions or heavy molecules, often require integration times of several minutes due to the low source intensity or the high velocity selection. Here we present a scheme to suppress the influence of such dephasing mechanisms—especially in the low-frequency regime—by analyzing temporal and spatial particle correlations available in modern detectors. Such correlations can reveal interference properties that would otherwise be washed out due to dephasing by external oscillating signals. The method is shown experimentally in a biprism electron interferometer where a perturbing oscillation is artificially introduced by a periodically varying magnetic field. We provide a full theoretical description of the particle correlations where the perturbing frequency and amplitude can be revealed from the disturbed interferogram. The original spatial fringe pattern without the perturbation can thereby be restored. The technique can be applied to lower the general noise requirements in matter-wave interferometers. It allows for the optimization of electromagnetic shielding and decreases the efforts for vibrational or temperature stabilization.

We present families of beating dark-dark solitons in spin-orbit (SO) -coupled Bose-Einstein condensates. These families consist of solitons residing simultaneously in the two bands of the energy spectrum. The soliton components are characterized by two different spatial and temporal scales, which are identified by a multiscale expansion method. The solitons are “beating” ones, as they perform density oscillations. The characteristic frequency of the latter is relevant to Zitterbewegung (ZB) oscillations, which were recently observed in experiments with SO-coupled condensates [C. Qu et al., Phys. Rev. A 88, 021604(R) (2013); L. J. LeBlanc et al., New J. Phys. 15, 073011 (2013)]. We find that spin oscillations may occur, depending on the parity of each soliton branch, which consequently lead to ZB oscillations of the beating dark solitons. Analytical results are corroborated by numerical simulations, illustrating the robustness of the solitons.