We study the existence of absolutely maximally entangled (AME) states in quantum mechanics and its applications to quantum information. AME states are characterized by being maximally entangled for all bipartitions of the system and exhibit genuine multipartite entanglement. With such states, we present a parallel teleportation protocol which teleports multiple quantum states between groups of senders and receivers. The notable features of this protocol are that (i) the partition into senders and receivers can be chosen after the state has been distributed, and (ii) one group has to perform joint quantum operations while the parties of the other group only have to act locally on their system. We also prove the equivalence between pure state quantum secret sharing schemes and AME states with an even number of parties.

Recently [Phys. Rev. Lett. 108, 253005 (2012)], we observed that approximate Hartree-exchange-correlation potentials constructed from electron densities depleted at the highest-occupied molecular orbital (HOMO) level mimic the exact potential at intermediate distances from the nuclei; we then used this fact to obtain accurate Rydberg excitation energies of atoms and molecules within time-dependent density-functional linear-response theory employing standard semilocal approximations. Here we reinterpret this method as a form of self-interaction correction for Kohn-Sham potentials. We show that the greatest improvement in HOMO eigenvalues occurs when the charge removed from the HOMO level is about $\frac{1}{2}$ electron, which explains why the Slater transition-state method works well for predicting ionization energies. The greatest improvement in Kohn-Sham orbital gaps, however, is achieved when about $\frac{1}{4}$ electron is removed, which is why smaller HOMO depopulations are required for obtaining accurate excitation energies. The relationship between our self-interaction correction scheme, Slater's transition-state technique, and the $X\alpha$ method is also clarified.

Linear-response methods, based on the time-dependent variational coupled-cluster or the unitary coupled-cluster model, and truncated at the second order according to the Møller-Plesset partitioning, i.e., the TD-VCC[2] and TD-UCC[2] linear-response methods, are presented and compared. For both of these methods a Hermitian eigenvalue problem has to be solved to obtain excitation energies and state eigenvectors. The excitation energies thus are guaranteed always to be real valued, and the eigenvectors are mutually orthogonal, in contrast to response theories based on “traditional” coupled-cluster models. It turned out that the TD-UCC[2] working equations for excitation energies and polarizabilities are equivalent to those of the second-order algebraic diagrammatic construction scheme ADC(2). Numerical tests are carried out by calculating TD-VCC[2] and TD-UCC[2] excitation energies and frequency-dependent dipole polarizabilities for several test systems and by comparing them to the corresponding values obtained from other second- and higher-order methods. It turns out that the TD-VCC[2] polarizabilities in the frequency regions away from the poles are of a similar accuracy as for other second-order methods, as expected from the perturbative analysis of the TD-VCC[2] polarizability expression. On the other hand, the TD-VCC[2] excitation energies are systematically too low relative to other second-order methods (including TD-UCC[2]). On the basis of these results and an analysis presented in this work, we conjecture that the perturbative expansion of the Jacobian converges more slowly for the TD-VCC formalism than for TD-UCC or for response theories based on traditional coupled-cluster models.

The induced absorption or annihilation of ${\pi }^{-}$, $K^{-}$, and $\overline{p}$ in collisions of hadronic hydrogen atoms in excited states with ordinary hydrogen in the ground state is treated in a unified manner with the elastic scattering, Stark transition, and Coulomb de-excitation in the framework of the close-coupling approach. The close-coupling approach is generalized to include both open andclosed channels corresponding to stable and unstable states of the hadronic atom. Calculations are performed using the basis sets including all states of hadronic atoms with a principal quantum number from $n=1$ up to $n_{\max }=8$. The general features of induced-absorption cross sections are studied in a wide range of complex energy-shift values. The cross sections of all processes are calculated for ${\pi }^{-}p$, $K^{-}p$, and $\overline{p}p$ atoms with principal quantum numbers $n=2$–8 and kinetic energies from 0.001 up to 100 eV. The validity of the previous quantum-mechanical and semiclassical models is critically discussed.

The lifetime of the $1s{}^{2}2s3p$ ${}^3{P}_0$ level of selected Be-like ions, from $Z=5$ to $Z=92$, is calculated using the multiconfiguration Dirac-Fock method including QED corrections. Full correlation up to the $4f$ subshell in both initial and final levels for all possible decay modes was included. The results are in reasonable agreement with the scarce existing experimental and theoretical data.

We study the interaction between a neutral atom or molecule and a conductor-patched dielectric surface. We model this system by a perfectly reflecting disk lying atop a nondispersive dielectric half-space, both interacting with the neutral atom or molecule. We assume the interaction to be nonretarded and at zero temperature. We find an exact solution to this problem. In addition, we generate a number of other useful results. For the case of no substrate, we obtain the exact formula for the van der Waals interaction energy of an atom near a perfectly conducting disk. We show that the force acting on an atom that is polarized in the direction normal to the surface of the disk displays intricate behavior. This part of our results is directly relevant to recent matter-wave experiments in which cold molecules are scattered by a radially symmetric object in order to study interference patterns and the so-called Poisson spot. Furthermore, we give an exact expression for the nonretarded limit of the dispersion force potential between an atom and a perfectly conducting bowl.

In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the $2p^{5}3s$ configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the ${}^3{P}_1^o{\text{−}}^1{S}_0$ transition by 17$\%$. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths, and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the ${}^3{P}_2^o{\text{−}}^1{S}_0$ $M2$ transition for which discrepancies of around 15$\%$ between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the ${}^3{P}_0^o$ and ${}^3{P}_2^o$ metastable states is investigated for the ${}^{21}$Ne isotope ($I=3/2$). We find that hyperfine interactions reduce the lifetimes drastically. For the ${}^3{P}_0^o$ state the lifetime is decreased by a factor of 630.

The absolute frequency measurement of thallium $6P_{1/2}\to 7S_{1/2}$ transitions using a self-referencing optical frequency comb is reported. Our results can be used as a benchmark for the accurate wave-function calculations of heavy atoms, and then improve the calculations of the atomic parity-nonconservation amplitude. The frequency centers have been precisely determined by the Doppler-free saturation spectroscopy utilizing a pair of the counterpropagating laser beams intersecting with a thallium atomic beam. We have achieved the absolute frequency determination of the transition with an accuracy of 350 kHz. The isotope shift and hyperfine splittings are also deduced from our results. The hyperfine splittings of the $7S_{1/2}$ state are improved to sub-MHz accuracy. Meanwhile, the nuclear isotopic changes resulting from the $7S_{1/2}$ and $6P_{1/2}$ hyperfine anomalies are in agreement with earlier measurements.

Electron-argon scattering in the presence of a linearly polarized, low-frequency laser field is studied theoretically. The scattering geometries of interest are small angles where momentum transfer is nearly perpendicular to the field, which is where the Kroll-Watson approximation has the potential to break down. The Floquet $R$ matrix method solves the velocity gauge Schrödinger equation, using a larger reaction volume than previous treatments in order to carefully assess the importance of the long-range polarization potential to the cross section. A comparison of the cross sections calculated with the target potential fully included inside 20 and 100 a.u. shows no appreciable differences, which demonstrates that the long-range interaction cannot account for the high cross sections measured in experiments.

Sequential multiphoton $L$-shell ionization of hydrogen sulfide exposed to intense femtosecond pulses of 1.25-keV x rays has been observed via photoelectron, Auger electron, and ion time-of-flight spectroscopies. Monte Carlo simulations based on relativistic Dirac-Hartree-Slater calculations of Auger decay rates in sulfur with single and double $L$-shell vacancies accurately model the observed spectra. While single-vacancy-only calculations are surprisingly accurate even at the high x-ray intensity used in the experiment, calculations including double-vacancy states improve on yield estimates of highly charged sulfur ions. In the most intense part of the x-ray focal volume, an average molecule absorbs more than five photons, producing multiple $L$-shell vacancies in 17$\%$ of photoionization events according to simulation. For 280-fs pulse duration and ∼10${}^{17}$ W cm${}^{-2}$ focal intensity, the yield of S${}^{13+}$ is ∼1$\%$ of the S${}^{3+}$ yield, in good agreement with simulations. An overabundance of S${}^{12+}$, and S${}^{14+}$ observed in the experimental ion spectra is not predicted by either single-vacancy or double-vacancy calculations.

We introduce the time-dependent restricted-active-space configuration-interaction method to solve the time-dependent Schrödinger equation for many-electron atoms, and particularly apply it to the treatment of photoionization processes in atoms. The method is presented in a very general formulation and incorporates a wide range of commonly used approximation schemes, such as the single-active electron approximation, time-dependent configuration interaction with single-excitations, or the time-dependent $R$-matrix method. We prove the applicability of the method by calculating the photoionization cross sections of helium and beryllium, as well as the x-ray–IR pump-probe ionization of beryllium.

Single-photon ionization of the HeH${}^{2+}$ molecular ion exposed to an attosecond x-ray laser pulse is investigated for photon energies of 200 and 300 eV. In the fixed-nuclei approximation, the temporal response of the system is obtained by solving the time-dependent Schrödinger equation through an ab initio time-dependent grid-based discrete-variable representation formulated in two-center prolate spheroidal coordinates. The two-center interference effect is clearly observable in the excited $2p\sigma$ state, whereas interference patterns almost disappear, in both the parallel and perpendicular geometries, when the system is started from the $1s\sigma$ ground state. The angular distributions are asymmetric with respect to the center between the helium and hydrogen nuclei. For the $2p\sigma$ state in the parallel geometry, a dynamically forbidden mode of photoionization is observed only on one side of the two nuclei, with the details depending on the laser parameters and the internuclear separation. We also address the similarities and differences between a plane-wave model for the ejected electron with a linear combination of atomic orbitals for the molecular bound states and the classical double-slit-like interference pattern.

Existing techniques for synthesizing gauge fields are able to bring a two-dimensional cloud of harmonically trapped bosonic atoms into a regime where the occupied single-particle states are restricted to the lowest Landau level. Repulsive short-range interactions drive various transitions from fully condensed into strongly correlated states. In these different phases we study the response of the system to quasihole excitations induced by a laser beam. We find that in the Laughlin state the quasihole performs a coherent constant rotation around the center, ensuring conservation of angular momentum. This is distinct to any other regime with higher density, where the quasihole is found to decay. At a characteristic time, the decay process is reversed, and revivals of the quasihole can be observed in the density. Measuring the period and position of the revival can be used as a spectroscopic tool to identify the strongly correlated phases in systems with a finite number of atoms.

We predict the emergence of a roton minimum in the dispersion relation of elementary excitations in cold atomic gases in the presence of diffusive light. In large magneto-optical traps, multiple scattering of light is responsible for the collective behavior of the system, which is associated to an effective Coulomb-like interaction between the atoms. In optically thick clouds, the rescattered light undergoes diffusive propagation, which is responsible for a stochastic short-range force acting on the atoms. We show that the dynamical competition between these two forces is by the appearance of a roton minimum in the dispersion relation. Making use of the fluctuation-dissipation theorem, we show that the roton minimum is related to classical long-range order in the system.

In this paper we investigate whether it is, in general, possible to substitute maximally path-entangled states, namely, NOON states, with classical light in Doppleron-type resonant multiphoton detection processes by studying adaptive phase measurement with classical light. We show that multiphoton detection probability using classical light coincides with that of NOON states and the multiphoton absorption rate is not hindered by the spatially unconstrained photons of the classical light in our scheme. We prove that the optimal phase variance with classical light can be achieved and scales the same as that using NOON states.

By restating geometrical optics within the field-theoretical approach, the classical concept of a photon (and, more generally, any elementary excitation) in an arbitrary dispersive medium is introduced, and photon properties are calculated unambiguously. In particular, the canonical and kinetic momenta carried by a photon, as well as the two corresponding energy-momentum tensors of a wave, are derived from the first principles of Lagrangian mechanics. As an example application of this formalism, the Abraham-Minkowski controversy pertaining to the definitions of these quantities is resolved for linear waves of arbitrary nature, and corrections to the traditional formulas for the photon kinetic energy-momentum are found. Several other applications of axiomatic geometrical optics to electromagnetic waves are also presented.

Strongly asymmetric Fabry-Perot-type transmission arising at the two-way coupling has been studied in the case of normal incidence for slabs of two-dimensional photonic crystals (PCs) with one-sided corrugations that are made of linear isotropic materials. Comparing to the scenario of unidirectional transmission known for the structures with broken spatial inversion symmetry that requires zero order being uncoupled, in the studied mechanism zero order is either the sole order or one of the orders that may be coupled to a Floquet-Bloch mode. Contrary to the earlier studies of asymmetric transmission at the coupled zero order, structures with nondeep corrugations are considered, which allow one to combine Fabry-Perot-type total-transmission maxima with diffractions in a desired way. At a proper choice of PC lattice and corrugation parameters, higher orders can dominate in Fabry-Perot-type transmission at the noncorrugated-side illumination and also at the total-transmission maxima, whereas only zero order contributes to the transmission at the corrugated-side illumination. As a result, strong asymmetry can be obtained without uncoupling of zero order but it invokes the unidirectional contribution of higher orders. The presented results show that the entire structure can be approximately decomposed into the two independent, regular and grating (nonregular), parts whose contributions to the transmission are additive. Multiple asymmetric transmission maxima can coexist with a rather high equivalent group index of refraction. Possible applications of the studied transmission mechanism are discussed.

We present a class of exact nonstationary solutions of Maxwell equations in vacuum from dipole pulse theory: electric and magnetic dipole pulses. These solutions can provide for a very efficient focusing of electromagnetic field and can be generated by $4\pi$ focusing systems, such as parabolic mirrors, by using radially polarized laser pulses with a suitable amplitude profile. The particular cases of a monochromatic dipole wave and a short dipole pulse with either quasi-Gaussian or Gaussian envelopes in the far-field region are analyzed and compared in detail. As a result, we propose how to increase the maximum field amplitude in the focus by properly shaping the temporal profile of the input laser pulses with given main wavelength and peak power.

Using pump-probe spectroscopy, strong-field enhanced-ionization is found in an inner orbital of I${}_2$. A wave packet is launched in the $B$ state of I${}_2$, whose valence orbitals are ${\sigma }_g^2{\pi }_u^4{\pi }_g^3{\sigma }_u^1$, and singly ionized to the $\text{I}+{\text{I}}^{+}$ dissociation channel. The ionization signal peaks at two different internuclear separations: $\sim$7.3 and $\sim$8.7 a.u. The latter shows enhanced ionization of the ${\sigma }_u$ state which has been studied before with the ${{\text{I}}_2}^{+}$ signal. However, the peak at smaller $R$ corresponds to enhanced ionization of the ${\sigma }_g$ state. The peak at $\sim$8.7 a.u. in the dissociating channel reveals that there could be strong mixing of different molecular orbitals when the two iodine atoms are pulled apart.

We present a set of Bell inequalities for multiqubit quantum systems. These Bell inequalities are shown to be able to detect multiqubit entanglement better than previous Bell inequalities such as Werner-Wolf-Zukowski-Brukner ones. Computable formulas are presented for calculating the maximal violations of these Bell inequalities for any multiqubit states.