We investigate relations between the global squeezing of composite systems and the local squeezing of subsystems. For the pure symmetric product states, the global squeezing parameter is found to be equal to the local one for both spin and bosonic systems. Hence, a pure symmetric state is entangled if the global parameter is not equal to the local one. Two origins of the global squeezing are identified: one is from the local squeezing and the other from quantum correlations. For both spin and bosonic systems, we find that the entanglement can lead to a smaller global squeezing parameter; namely, the global squeezing is enhanced.

Nonlocal two-qubit gates are geometrically represented by tetrahedron known as Weyl chamber within which perfect entanglers form a polyhedron. We identify that all edges of the Weyl chamber and polyhedron are formed by single parametric gates. Nonlocal attributes of these edges are characterized using entangling power and local invariants. In particular, ${\text{SWAP}}^{-\alpha }$ family of gates with $0\le \alpha \le 1$ constitutes one edge of the Weyl chamber with ${\text{SWAP}}^{-1/2}$ being the only perfect entangler. Finally, optimal constructions of controlled-NOT using ${\text{SWAP}}^{-1/2}$ gate and gates belong to three edges of the polyhedron are presented.

We consider blocks of quantum spins in a chain at thermal equilibrium, focusing on their properties from a thermodynamical perspective. In a classical system the temperature behaves as an intensive magnitude, above a certain block size, regardless of the actual value of the temperature itself. However, a deviation from this behavior is expected in quantum systems. In particular, we see that under some conditions the description of the blocks as thermal states with the same global temperature as the whole chain fails. We analyze this issue by employing the quantum fidelity as a figure of merit, singling out in detail the departure from the classical behavior. As it may be expected, we see that quantum features are more prominent at low temperatures and are affected by the presence of zero-temperature quantum phase transitions. Interestingly, we show that the blocks can be considered indeed as thermal states with a high fidelity, provided an effective local temperature is properly identified. Such a result may originate from typical properties of reduced subsystems of energy-constrained Hilbert spaces. Finally, the relation between local and global temperatures is analyzed as a function of the size of the blocks and the system parameters.

We present an efficient scheme for generating high-fidelity entanglement locally which is essential for quantum repeater protocols. Two local “polarization” entangled states of atomic ensembles $u$ and $d$ are generated by absorbing a single photon emitted by on-demand single-photon sources, based on which high-fidelity local entanglement between four ensembles can be established efficiently through Bell-state measurement. Entanglement in basic links and entanglement connection between links are carried out by the use of two-photon interference. In addition to being robust against phase fluctuations in the quantum channels, this scheme may speed up quantum communication with higher fidelity compared with the partial read protocol [Sangouard et al., Phys. Rev. A 77, 062301 (2008)] which may generate entanglement most quickly among the previous schemes with the same ingredients.

The many-body perturbation theory in the Hedin’s $GW$ approximation is nowadays a common tool to carry out calculations in solids and molecular systems. Nevertheless a lot of theoretical issues concerning the self-interaction problem remain unresolved in the basic theory of this approximation. In this paper we carry out calculations in some very simple exactly solvable model systems and demonstrate that at this level of approach there are self-interaction problems in the correlation part that seriously affect the final results. This is especially important in the low-density regime. We also have carried out the calculations using different input data coming from the local-density approximation (LDA), generalized gradient approximation (GGA), and exact solutions of the Schrödinger equation to check how much affected are the final $G_0{W}_0$ results by the election of the input data. We have found that the final results inherit the errors from the input data and that only good results can be achieved if the input data are very close to (or are) the exact ones.

Experimental and calculated differential cross sections (DCSs) for electron-impact excitation of the (010) bending mode and unresolved (100) symmetric and (001) antisymmetric stretching modes of water are presented. Measurements are reported at incident energies of 1–100 eV and scattering angles of $10°–130°$ and are normalized to the elastic-scattering DCSs for water determined earlier by our group. The calculated cross sections are obtained in the adiabatic approximation from fixed-nuclei, electronically elastic scattering calculations using the Schwinger multichannel method. The present results are compared to available experimental and theoretical data.

We present a study of multimode effects in dissociative electron attachment to ${\text{CF}}_3\text{Cl}$ molecules using a time-independent version of the local complex potential theory. Symmetric stretch C-Cl vibrations ${\nu }_3$ and symmetric deformation (or so-called umbrella) vibrations ${\nu }_2$ are included. The neutral and anion potential energy surfaces are calculated using the second-order Møller-Plesset perturbation theory with an empirical adjustment of the vertical attachment energy. The final-state vibrational distribution in the ${\text{CF}}_3\left({\nu }_2\right)$ fragment is dominated by the ${\nu }_2=2$ state. We also find an increase in the total cross section as compared with the one-dimensional calculations. This is explained by an increase in the anion survival probability.

The high-order harmonic generation for a one-dimensional hydrogen atom model in the combination of the chirped laser pulse and static field is theoretically investigated. Here we explore a novel physical mechanism of the significant extension of high-order-harmonic generation cutoff based on three-step model. It is shown that due to the asymmetry of the combined field the cutoff is substantially extended. If appropriate parameters are chosen, the cutoff of high-order harmonic generation can reach $I_p+42U_p$. Furthermore, an ultrabroad supercontinuum spectrum can be generated. When the phases are properly compensated for, an isolated 10 as pulse can be obtained.

We propose the subwavelength localization via adiabatic passage (SLAP) technique to coherently achieve state-selective patterning of matter waves well beyond the diffraction limit. The SLAP technique consists in coupling two partially overlapping and spatially structured laser fields to three internal levels of the matter wave yielding state-selective localization at those positions where the adiabatic passage process does not occur. We show that by means of this technique matter wave localization down to the single nanometer scale can be achieved. We analyze in detail the potential implementation of the SLAP technique for nanolithography with an atomic beam of metastable ${\text{Ne}}^{\ast }$ and for coherent patterning of a two-component ${}^{87}\text{R}\text{b}$ Bose-Einstein condensate.

We propose the realization of topological quantum states in a cold-atom system, using a two-dimensional hexagonal optical lattice and a light-induced periodic vector potential. A necessary condition for observing the topological states is the realization of a confining potential with a flat bottom and sharp boundaries. To probe the topological states, we propose to load bosons into the characteristic edge states and image them directly. The possibility of mapping out the edge states and controlling the optical lattice and vector potentials offers opportunities for exploring topological phases with no equivalent in condensed-matter systems.

We address the elliptically shaped vortex solitons in defocusing nonlinear media imprinted with a composite Mathieu lattice. Elliptic vortices feature anisotropic patterns both in intensity and phase, and can only exist when their energy flows exceed some certain threshold. Single-charged elliptic vortices are found to arise via bifurcation from dipole modes, which is an example in the context of optics studies of symmetry breaking bifurcations for the phase dislocations of different dimensionalities. Higher-order elliptic vortices with topological charge $S$ could exhibit spatially separated $S$ single-charged phase singularities, leading to their stabilization. The salient features of reported elliptic vortices qualitatively hold for other elliptic shaped confining potentials.

Stimulated Raman scattering has been harnessed to produce the first silicon lasers and amplifiers. The Raman effect can also produce intensity-dependent nonlinear loss through a corollary process, inverse Raman scattering (IRS). This process has never been observed in a semiconductor. We demonstrate IRS in silicon—a process that is substantially modified by optically generated free carriers—achieving attenuation levels $>15\text{dB}$ with a pump intensity of $4\text{GW}/{\text{cm}}^2$. Surprisingly, free-carrier absorption, the detrimental effect that generally suppresses nonlinear effects in silicon, actually facilitates IRS by delaying the onset of contamination from coherent anti-Stokes Raman scattering. Silicon-based IRS could be a valuable tool for chip-scale signal processing.

We describe a strategy to cloak twisted domains where, in contrast to the usual cloaks, the outer domain does not necessarily need to possess a direct connection to the point of inflation. The strategy consists of two steps. At first, a transformation is applied to untwist the geometry. Then, a second transformation is applied to create a point-transformed cloak with vanishing scattering cross section. As an extreme, yet analytical example, we construct a cloak having the shape of a spiral. Full-wave simulations confirm that electromagnetic waves impinging on the spiral-type cloak are bent around the structure with no discernible scattering.

We develop an approach to coherence between two scalar harmonic light vibrations derived from the ensemble interpretation of statistical optics. Coherence is presented as a statistical variable itself that turns out to be the phase difference between the two vibrations. This provides a natural and simple extension of second-order coherence to cover more complicated situations. This includes in a single formalism both classic and quantum light states, allowing the most accurate interferometric measurements, even if they are incoherent according to the standard second-order approach.

The monogamy inequality in terms of the concurrence, called the Coffman-Kundu-Wootters inequality [V. Coffman et al., Phys. Rev. A 61, 052306 (2000)], and its generalization [T. J. Osborne and F. Verstraete, Phys. Rev. Lett. 96, 220503 (2006)] hold on general $n$-qubit states including mixed ones. In this Brief Report, we consider the monogamy inequalities in terms of the fully entangled fraction and the teleportation fidelity. We show that the monogamy inequalities do not hold on general mixed states, while the inequalities hold on $n$-qubit pure states.

We propose a method to control the atomic dynamics in the presence of electromagnetic fields. Instead of measuring the population dynamics, we focus on the possibility of controlling the Pancharatnam phase. For a two-level system we find that this phase can be optically induced and controlled by the phase shift. More importantly, the nonlinear interaction between the atom and the field leads to an enhanced sensitivity for the control of the atomic phase evolution and system dynamics.

Nonadiabatic transitions are known to be major loss channels for atoms in magnetic traps but have thus far not been experimentally reported upon for trapped molecules. We have observed and quantified losses due to nonadiabatic transitions for three isotopologues of ammonia in electrostatic traps by comparing the trapping times in traps with a zero and a nonzero electric field at the center. Nonadiabatic transitions are seen to dominate the overall loss rate even for the present samples that are at relatively high temperatures of 30 mK. It is anticipated that losses due to nonadiabatic transitions in electric fields are omnipresent in ongoing experiments on cold molecules.

We implemented a multipulse interferometer scheme that allows us to study a quantum kicked rotor by observing dephasing of momentum coherence. Our study shows that momentum coherence can be nearly perfectly preserved under conditions where the mean energy as a function of the kick number is known to increase without bound. The accompanying width narrowing of these coherences may provide a new method for accurate measurement of the recoil frequency.

We discuss the Aharonov-Bohm effect of a magnetic flux for its influence on a two-dimensional quantum cloak. It is shown that the matter wave of a charged particle under the global influence of the Aharonov-Bohm effect can still be perfectly cloaked and guided by the quantum cloak. Since the presence of the global influence of a magnetic flux on charged particles is universal, the perfect cloaking and guiding nature not only provides an ideal setup to cloak an object from matter waves but also provides an ideal setup to test the global physics of charged matter waves in the presence of a bare magnetic flux.

We demonstrate that electromagnetic energy can be efficiently guided along a single chain, around a corner, and split at forked structures below the diffraction limit with the use of appropriate dielectric particle arrays. The fields are confined to a region with the transverse width less than half of the guided wavelength. Our results give an explicit demonstration that the dielectric based subwavelength photonic circuit is achievable, providing an alternative to the surface-plasmon-based metallic counterpart.