In an effort to obtain a microscopic understanding of the origin of vuv emission from inert heavy-atom gas mixtures we present results from relativistic calculations of the krypton-xenon spectrum in the 68 000 ${\mathrm{cm}}^{\mathrm{-}1}$ region. Calculations carried out on the interatomic interaction in the ground and in the low-lying spin-orbit excited states $\left[0^{-}{(}^3{P}_2\right),0^{+}{(}^3{P}_1),{1(}^3{P}_1),{1(}^3{P}_2),{2(}^3{P}_1)]$ of the krypton-xenon dimer are presented. The calculations were executed in a two-step procedure in which the CCSD(T) model for the ground state and the CCSD response theory model for the excited states were used to obtain spin-free potential curves in the first step. A perturbational treatment of the spin-orbit interaction within the atomic mean-field approximation was applied in the next step. Large-core quasirelativistic effective core potentials with richly augmented valence basis sets and midbond functions were used. All calculations were corrected for basis set superposition errors by applying the counterpoise method. For all involved states, spin-orbit perturbed potential energy curves were computed and equilibrium geometries, potential well depths, and local extrema were determined. Vibrational analysis and Franck-Condon factors for the ground and $0^{+}{(}^3{P}_1{),1(}^3{P}_1)$ states were also calculated. The geometry dependence of the electronic dipole transition matrix elements between all involved excited states and the ground state was investigated. Excitation energies and potentials were obtained that are in excellent agreement with results based on fitting to experimental data. Out of some earlier disparate experimental assignments of the character of the excited states of the KrXe complex, the present results adhere most closely to the ones presented by Pibel et al. [J. Chem. Phys. 101, 10 242 (1994)]. Analyzed together with the experimental data, the theoretical results provide a clear picture of the organization of exciplex states and of the origin of strong vuv emission from these states that follows from binary collisions of the heavy inert Kr and Xe atoms.

We present a precise calculation of the nonrelativistic energies and Auger decay widths for the Condo-type metastable states of exotic helium atoms ${\mathrm{He}}^{+}{X}^{-},$ where $X^{-}$ stands for one of the negatively charged heavy particles ${\mu }^{-},$ ${\pi }^{-},$ or $K^{-}.$ It has been found that some of the states in muonic and pionic atoms have an anomalously small Auger rate and decay predominantly via slow radiative transitions with the time up to a few hundreds of nanoseconds (muonic atoms) or via a pion decay “at rest” $\left({\mathrm{He}}^{+}{\pi }^{-}\right).\mathrm{}$

We demonstrate the possibility of determining the dependence of ionization probabilities on the alignment of molecules in a double-pulse laser experiment. A short pump pulse is used to generate a rotational wave packet which produces aligned molecules during the periods of rotational wave packet revival. The ionization probabilities by a subsequent probe laser vs the time delay are calculated for ${\mathrm{O}}_2$ and ${\mathrm{N}}_2$ molecules at different temperatures. Distinct time dependence is predicted, and the results are interpreted in terms of the geometry of the charge distributions of the valence electrons of the two molecules.

The field fluctuations of a Bose-Einstein condensate can be studied in terms of the first-order correlation function, which obeys a Yukawa-like equation already introduced in a previous work and expressed here in a real and complex notation. When the equation is reformulated using the number-conserving Bogoliubov approximation, it yields results that present quantitative differences with respect to the standard symmetry-breaking approach. Finally, we introduce an approximation to evaluate the correlation function for sufficiently high temperatures.

In this paper, we report a scheme for the generation of a pulsed polarization entangled-photon pair in a two-crystal geometry. These two crystals are oriented with their optical axes aligned in a perpendicular plane, stacked in the vertical direction. The stack direction and the pass direction of pump laser are orthogonal. This scheme has some advantages compared to other schemes: no time compensation or narrow-band filter is needed, it is insensitive to the thickness of the nonlinear crystal. As a demonstration of its workability, we get more than 86% high visibility of two-photon quantum interference experimentally for the polarization variable, without any time compensation and narrow-band filter. This scheme may be a useful technique for the generation of a pulsed entangled-photon pair.

While ultimately they are described by quantum mechanics, macroscopic mechanical systems are nevertheless observed to follow the trajectories predicted by classical mechanics. Hence, in the regime defining macroscopic physics, the trajectories of the correct classical motion must emerge from quantum mechanics, a process referred to as the quantum to classical transition. Extending previous work [Bhattacharya, Habib, and Jacobs, Phys. Rev. Lett. 85, 4852 (2000)], here we elucidate this transition in some detail, showing that once the measurement processes that affect all macroscopic systems are taken into account, quantum mechanics indeed predicts the emergence of classical motion. We derive inequalities that describe the parameter regime in which classical motion is obtained, and provide numerical examples. We also demonstrate two further important properties of the classical limit: first, that multiple observers all agree on the motion of an object, and second, that classical statistical inference may be used to correctly track the classical motion.

By using the complex angular momentum method, we provide a semiclassical analysis of electron scattering by a magnetic vortex of Aharonov-Bohm type. Regge poles of the S matrix are associated with surface waves orbiting around the vortex and supported by a magnetic field discontinuity. Rapid variations of sharp characteristic shapes can be observed on scattering cross sections. They correspond to quasibound states which are Breit-Wigner-type resonances associated with surface waves and which can be considered as quantum analogues of acoustic whispering-gallery modes. Such a resonant magnetic vortex could provide a different kind of artificial atom while the semiclassical approach developed here could be profitably extended in various areas of the physics of vortices.

We calculate the static and dynamic single-particle correlation functions in one-dimensional (1D) trapped Bose gases and discuss experimental measurements that can directly probe such correlation functions. Using a quantized hydrodynamic theory for the low-energy excitations, we calculate both the static and dynamic single-particle correlation functions for a 1D Bose gas that is a phase-fluctuating quasicondensate. For the static (equal-time) correlation function, our approximations and results are equivalent to those of Petrov, Shlyapnikov, and Walraven. The Fourier transform of the static single-particle correlation function gives the momentum distribution, which can be measured using Doppler-sensitive Bragg scattering experiments on a highly elongated Bose gas. We show how a two-photon Raman out-coupling experiment can measure the characteristic features of the dynamic or time-dependent single-particle correlation function of a 1D Bose quasicondensate.

We study the behavior of a type-II degenerate parametric amplifier in a cavity with nonorthogonal polarization eigenmodes. The mode nonorthogonality is achieved by introducing circular birefringence and linear dichroism. We use a scattering matrix formalism to investigate the role of excess quantum noise in such a device. Since only two modes are involved we are able to derive an analytical expression for the twin-photon generation rate measured outside the cavity as a function of the degree of mode nonorthogonality. Contrary to recent claims we conclude that there is no evidence of excess quantum noise for a parametric amplifier working so far below threshold that spontaneous processes dominate. Using the same scattering matrix formalism we also investigate the output spectrum of the amplifier near the threshold of parametric oscillation. We find optical band structures very similar to those known for passive ring cavities. These optical band structures are studied as a function of mode nonorthogonality and mirror reflectivity.

Dielectronic recombination (DR) for He-like ${\mathrm{Ar}}^{16+}$ through both one-electron–one-photon and two-electron–one-photon (TEOP) stabilizations of Li-like states was studied with an electron-beam ion trap (EBIT). It turned out that this is an excellent method to investigate TEOP transitions. Its advantages are a high branching ratio for the TEOP transition and clean conditions under which spectator electrons are controlled. Further, state- and configuration-resolved KLL DR cross sections were obtained due to the unsurpassed electron energy resolution achieved in the EBIT in the energy range around 2 keV.

Using numerical simulations, we examine the wave-function probability density of a model two-electron atom exposed to intense femtosecond laser pulses. We determine numerically the lowest-lying energies and eigenstates of the model atom. This information is then used to identify resonance features within the double-ionization yield, defined as probability density in which both electrons are far from the nucleus, and the atomic levels responsible for these features. This resonance behavior is confirmed using two distinct procedures.

We have theoretically determined and experimentally confirmed that polychromatic multiphoton coherent excitation can be used to most efficiently achieve a selective total population inversion in a multilevel system. These results suggest a solution to the problem of using mesospheric sodium as a guidestar.

Using the Liouville space framework developed in nonlinear optics, we calculate the linear response functions and susceptibilities of Bose-Einstein condensates (BEC) subject to an arbitrary mechanical force. Distinct signatures of the dynamics of finite-temperature BEC are obtained by solving the Hartree-Fock-Bogoliubov theory. Numerical simulations of the position-dependent linear response functions of one-dimensional trapped BEC in the time and the frequency domains are presented.

Bipartite operations underpin both classical communication and entanglement generation. Using a superposition of classical messages, we show that the capacity of a two-qubit operation for error-free entanglement-assisted bidirectional classical communication cannot exceed twice the entanglement capability. In addition, we show that any bipartite two-qubit operation can increase the communication that may be performed using an ensemble by twice the entanglement capability.

It is proved from stated assumptions of nonrelativistic quantum mechanics based on the Schrödinger equation that identical spin-zero particles must obey symmetric statistics.

The problem of unambiguous state discrimination consists of determining in which of a set of known quantum states a particular system is. One is allowed to fail but not to make a mistake. The optimal procedure is the one with the lowest failure probability. This procedure has been extended to bipartite states where the two parties Alice and Bob are allowed to manipulate their particles locally and communicate classically in order to determine which of two possible two-particle states they have been given. The failure probability of this local procedure is the same as if the two particles were together in the same location. Here we examine the effect of restricting the classical communication between the parties, either allowing none or eliminating the possibility that one party’s measurement depends on the result of the other party’s. These issues are studied for two-qubit states, and optimal procedures are found. In some cases the restrictions cause increases in the failure probability, but in other cases they do not. Applications of this procedure, in particular to secret sharing, are discussed.

We introduce the quantum quincunx, which physically demonstrates the quantum walk and is analogous to Galton’s quincunx for demonstrating the random walk by employing gravity to draw pellets through pegs on a board, thereby yielding a binomial distribution of final peg locations. In contradistinction to the theoretical studies of quantum walks over orthogonal lattice states, we introduce quantum walks over nonorthogonal lattice states (specifically, coherent states on a circle) to demonstrate that the key features of a quantum walk are observable albeit for strict parameter ranges. A quantum quincunx may be realized with current cavity quantum electrodynamics capabilities, and precise control over decoherence in such experiments allows a remarkable decrease in the position noise, or spread, with increasing decoherence.

An alternative description of quantum scattering processes rests on inhomogeneous terms amended to the Schrödinger equation. We detail the structure of sources that give rise to multipole scattering waves of definite angular momentum, and introduce pointlike multipole sources as their limiting case. We obtain results for ballistic scattering in an external uniform force field, where we provide analytical solutions for both the scattering waves and the integrated particle flux. Our theory directly applies to p-wave photodetachment in an electric field. Furthermore, illustrating the effects of extended sources, we predict some properties of vortex-bearing atom laser beams outcoupled from a rotating Bose-Einstein condensate under the influence of gravity.

A model is proposed where two ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ nonlinear waveguides are contained in a cavity suited for second-harmonic generation. The evanescent wave coupling between the waveguides is considered as weak, and the interplay between this coupling and the nonlinear interaction within the waveguides gives rise to quantum violations of the standard quantum limit. Pronounced twin-beam behavior is observed as almost complete noise suppression in the difference as well as the sum of the waveguide intensities close to bistable transitions, self-pulsing instabilities as well as the transition from symmetric to asymmetric states. The correlations imply strong correlations and anticorrelations induced by the coupling. The violations of the standard quantum limit are particularly strong when two instabilities are competing. The results are based on the full quantum Langevin equations derived from the boson operator Hamiltonian and including cavity damping effects. The intensity correlations of the output fields are calculated semianalytically using a linearized version of the Langevin equations derived through the positive-P representation. Confirmation of the analytical results are obtained by numerical simulations of the nonlinear Langevin equations derived using the truncated Wigner representation.

A theory of spontaneous pair production is developed for the inverse process of the Čerenkov radiation. In the case of a free-electron gas, this “Čerenkov pair production” may occur if the relativistic plasma frequency of the gas ${\omega }_{\mathrm{rp}}$ satisfies $ħ{\omega }_{\mathrm{rp}}>{2m}_0{c}^2,$ which may hold in very dense matter, such as neutron stars.