The electric dipole moment (EDM) of a particle violates both time-reversal (T) and space-reflection (P) symmetries. There have been recent suggestions to investigate the electron EDM using solid-state experiments. These experiments could improve the sensitivity compared to present atomic and molecular experiments by several orders of magnitude. In the present paper we calculate the expected effect. We also suggest that this kind of experiment is sensitive to T,P violation in nuclear forces and calculate the effects caused by the nuclear Schiff moment. The compounds under consideration contain magnetic ${\mathrm{Gd}}^{3+}$ ions and oxygen ${\mathrm{O}}^{2-}$ ions. We demonstrate that the main mechanism for the T,P-odd effects is related to the penetration of the oxygen $2p$ electrons into the Gd core. All the effects are related to the deformation of the crystal lattice.

We present a general formulation to suppress pure dephasing by multipulse control. The formula is free from a specific form of interaction and is expressed in terms of the correlation function of an arbitrary system-reservoir interaction. We first apply the formula to a phenomenological two-level model where the correlation function of the interaction decays exponentially. In this case, we show analytically that the pure dephasing time is effectively lengthened by the multipulse control. Secondly, we apply the formula to the spin-boson model where a spin interacts nonlinearly with a boson reservoir. We find the multipulse control works well when the pulse interval is sufficiently shorter than the correlation time of the system-reservoir interaction. Moreover, in this case, the pure dephasing can also be suppressed by adjusting the pulse interval to the period of dynamical motion of the reservoir.

We propose a quantum algorithm for solving combinatorial search problems that uses only a sequence of measurements. The algorithm is similar to quantum computation by adiabatic evolution, in that the goal is to remain in the ground state of a time-varying Hamiltonian. Indeed, we show that the running times of the two algorithms are closely related. We also show how to achieve the quadratic speedup for Grover’s unstructured search problem with only two measurements. Finally, we discuss some similarities and differences between the adiabatic and measurement algorithms.

It is known that unambiguous discrimination among nonorthogonal but linearly independent quantum states is possible with a certain probability of success. Here, we consider a variant of that problem. Instead of discriminating among all of the different states, we shall only discriminate between two subsets of them. In particular, for the case of three nonorthogonal states, $\{|{\psi }_1〉,|{\psi }_2〉,|{\psi }_3〉\},$ we show that the optimal strategy to distinguish $|{\psi }_1〉$ from the set $\{|{\psi }_2〉,|{\psi }_3〉\}$ has a higher success rate than if we wish to discriminate among all three states. Somewhat surprisingly, for unambiguous discrimination the subsets need not be linearly independent. A fully analytical solution is presented, and we also show how to construct generalized interferometers (multiport) which provide an optical implementation of the optimal strategy.

We characterize the class of all physical operations that transform Gaussian states to Gaussian states. We show that this class coincides with that of all operations that can be performed on Gaussian states using linear optical elements and homodyne measurements. For bipartite systems we characterize the processes that can be implemented by local operations and classical communication, as well as those that can be implemented using positive partial transpose preserving maps. As an application, we show that Gaussian states cannot be distilled by local Gaussian operations and classical communication. We also define and characterize positive (but not completely positive) Gaussian maps.

Pure inversion spectra for the $|J,K〉=|1,1〉$ level of ${}^{14}{\mathrm{ND}}_3$ and of ${}^{15}{\mathrm{ND}}_3$ are recorded at 10 kHz resolution using a molecular-beam microwave-UV double-resonance spectrometer. The observed spectra are fully assigned, and the energies of all $|J,K〉=|1,1〉$ hyperfine levels of both deuterated ammonia isotopomers are obtained. The shifting and splitting of the manifold of hyperfine levels in external electric fields is calculated and its implications for molecular-beam deceleration and trapping experiments are discussed.

Total electron-scattering cross section for ${\mathrm{CF}}_4$ has been measured in the energy range from 300 to 5000 eV. Semiempirical values for the total cross sections of ${\mathrm{CF}}_4,$ ${\mathrm{CF}}_3\mathrm{H},$ ${\mathrm{CF}}_2{\mathrm{H}}_2,$ and ${\mathrm{CFH}}_3$ between 0.5 and 10 keV are also given, obtained by means of a formula that depends only on the total number of electrons and the polarizability of the molecule, and which was previously deduced by the authors. Experimental and semiempirical values have been compared with previously published experimental data. Differential and integral elastic cross sections are given at several incident electron energies in the range from 100 to 10 keV, calculated by means of a scattering potential method, assuming that the independent-atom model is valid, and the results compared with other published data. Integral inelastic cross-section values are also given as the difference between the total cross section and the integral elastic cross-section data. Finally, in order to facilitate the use of the present results in computation work, our integral elastic and inelastic cross sections have been fitted to expressions based on Born-Bethe formulas, which allows one to obtain these cross sections at any energy within the energy range considered.

Absolute differential cross sections (DCSs) for elastic and vibrationally inelastic scattering of electrons from ${\mathrm{C}}_3{\mathrm{H}}_4$ isomers (allene and propyne) have been determined by a crossed-beam experiment in the energy range 1.5–100 eV and over the scattering angles between 15°–130°. The relative flow method was applied to normalize these cross sections, using helium as a standard. Clear evidence of the strong isomer effect has been observed in DCSs for both elastic and vibrational excitation processes, and the isomer effect still conspicuously persists in total elastic cross sections. Two resonance regions where the vibrational cross sections are strongly enhanced are observed in both allene and propyne below a few eV, while both the DCSs become identical at higher energies, hence weakening the isomer effect. More details of the observed mode selectivity are discussed based on the selection rules for vibrational excitation via a shape resonance as well as on an argument based on the angular correlation.

We report an investigation into the three-body fragmentation of a triatomic molecule ${\mathrm{H}}_2\mathrm{O}$ via the process of dissociative recombination (DR) of ${\mathrm{H}}_2{\mathrm{O}}^{+}.$ At 0-eV center-of-mass reaction energy two competing three-body fragmentation channels are available, both leading to the production of ground state H atoms $\mathrm{H}{(}^{2}S)$ but differing in the excitation state of the O atom fragment: $\mathrm{O}{(}^{3}P)$ and $\mathrm{O}{(}^{1}D).\mathrm{}$ Using time- and position-sensitive detectors in a triple-coincidence experiment, the fragments from the DR reaction are monitored and their momentum vectors and angular distribution recorded. From these data we determine that during the recombination process, oxygen atoms are produced in the ratio of 3.5(0.5):1 for $\mathrm{O}{(}^{3}P):\mathrm{O}{(}^{1}D),$ and find that the molecular geometry is not conserved and that the available reaction energy is randomly distributed between both hydrogen atoms. Quasiclassical trajectory calculations having the same initial starting conditions as those in the experiment have been carried out using calculated and measured ${\mathrm{H}}_2\mathrm{O}$ potential-energy surfaces, together with the knowledge of the various curve crossings, intersections, and estimations of the necessary coupling strengths. The results of these calculations, product state population distributions together with the geometries of the potential surfaces which contribute to the reaction, are compared to those observed in the experiment and allow questions to be answered on the dominance of three-body dissociation.

A time-dependent solution of the Schrödinger equation on a three-dimensional lattice is used to calculate proton-impact excitation cross sections for both the ground $\mathrm{}\left(2s\right)\mathrm{}$ and first excited $\mathrm{}\left(2p\right)\mathrm{}$ states of the neutral lithium atom. Total cross sections for the $2\overrightarrow{s}3l$ and $2\overrightarrow{p}3l$ excitations are compared with atomic-orbital close-coupling calculations at incident energies of 15–50 keV. In support of future experiments involving crossed ion, atom, and laser beams, total aligned cross sections for the $2p\overrightarrow{\sigma }3l$ and $2p\overrightarrow{\pi }3l$ excitations are presented over the same energy range. The ratio of aligned cross sections for certain excitations and incident energies is found to be almost a factor of 2.

We have developed a variable-spacing finite-difference algorithm that rapidly propagates the general solution of Schrödinger’s equation to large distances (whereupon it can be matched to asymptotic solutions, including the ionization channel, to extract the desired scattering quantities). The present algorithm, when compared to Poet’s corresponding fixed-spacing algorithm [R. Poet, J. Phys. B 13, 2995 (1980); S. Jones and A. T. Stelbovics, Phys. Rev. Lett. 84, 1878 (2000)], reduces storage by 98% and computation time by 99.98%. The method is applied to the Temkin-Poet electron-hydrogen model collision problem. Complete results (elastic, inelastic, and ionization) are obtained for low (17.6 eV), intermediate (27.2, 40.8, and 54.4 eV), and high (150 eV) impact energies.

We investigate the surface dielectric response of a free-electron gas to a projectile moving parallel to the surface. Three theoretical models are examined, viz., the specular reflection and the parallel dispersion models, and a here-proposed axial model. The mean-free path, the stopping, the straggling, and the self-induced potential at the projectile position, are calculated in terms of the distance of the projectile to the surface. Differences at level of energy-loss distribution are found. We conclude that the axial model is reliable, has a simple closed form and permits us to estimate the binary contribution.

The multiphoton resonant excitation of three-level atoms in a strong laser field is investigated. The creation of various superposition states is shown. For implementation of these effects either the mean dipole moment in the excited states of an atom or, in three-level systems, a transition dipole moment between excited states (with energies close enough to each other) must be nonzero. The time evolution of the system is found using a nonperturbative resonant approach. Our calculations for the hydrogen atom suggest that by the appropriate optical pulses with moderate strong intensities one can achieve various superposition states by multiphoton resonant excitation.

Bifurcations of classical orbits introduce divergences into semiclassical spectra which have to be smoothed with the help of uniform approximations. We develop a technique to extract individual energy levels from semiclassical spectra involving uniform approximations. As a prototype example, the method is shown to yield excellent results for photoabsorption spectra for the hydrogen atom in an electric field in a spectral range where the abundance of bifurcations would render the standard closed-orbit formula without uniform approximations useless. Our method immediately applies to semiclassical trace formulas as well as the closed-orbit theory and offers a general technique for the semiclassical quantization of arbitrary systems.

The dc and ac Josephson dynamics of a Bose-Einstein condensate in a double-well potential is analyzed in terms of transitions between energy eigenstates. By solving the time-independent and time-dependent Gross-Pitaevskii equations in one dimension, we identify population transfer associated with level crossings, and determine the critical velocity that characterizes the transition. We test the validity of a nonlinear two-state model, and show that for the experimentally interesting case, where the critical velocity is large, the influence of higher-lying states is important.

We analyze the collective excitations of a mixture of fermionic and bosonic helium atoms in a random-phase approximation. The spectrum is shown to be highly fragmented, and its spread increases with the size of the Bose-Einstein condensate formed by ${}^4\mathrm{He}$ atoms. In addition, the phase separation of the components at high boson numbers alters substantially the distribution of excited states. We also study the corresponding fluctuation shapes and emphasize their connection with the separation.

We report the experimental realization of the “active” quantum teleportation (QST) of a one-particle entangled qubit. This demonstration completes the original QST protocol and renders it available for actual implementation in quantum computation networks. It is accomplished by implementing an 8 m optical delay line and a single-photon triggered fast electro-optic Pockels cell. A large value of teleportation “fidelity” was attained: $F_a=(90\mathrm{}\mp 2)\%.$ Our work follows the line recently suggested by H. W. Lee and J. Kim [Phys. Rev. A $63,$ 012305 (2000)] and E. Knill, R. Laflamme, and G. Milburn [Nature (London) $409,$ 46 (2001)].

Photoionization and high-order harmonic generation (HHG) in molecular systems under the action of combined infrared femtosecond (fsec) and ultraviolet attosecond (asec) laser pulses are investigated numerically for a one-dimensional non-Born-Oppenheimer ${\mathrm{H}}_2^{+}$ ion. It is shown that punctual “turn-on” of an asec pulse can trigger the ionization process, which in turn leads to significant enhancement of HHG. The conversion efficiency of HHG can exceed the one obtained from a single fsec pulse by several orders and can be as high as ${10}^{-2}$ by controlling the recolliding electron responsible for the maximum order in HHG. The HHG spectrum becomes broader and quasicontinuous near the cutoff. This spectrum can be used to synthesize new single x-ray ultraviolet pulses as short as 250 asec.

In the case of a simple quantum system, we investigate the possibility of defining meaningful probabilities for a quantity that cannot be represented by a Hermitian operator. We find that the consistent-histories approach, recently applied to the case of quantum traversal time [N. Yamada, Phys. Rev. Lett. 83, 3350 (1999)], does not provide a suitable criterion and we dispute Yamada’s claim of finding a simple solution to the tunneling-time problem. Rather, we define the probabilities for certain types of generally nonorthogonal decomposition of the system’s quantum state. These relate to the interaction between the system and its environment, can be observed in a generalized von Neumann measurement, and are consistent with a particular class of positive-operator-valued measures.

We solve a problem of quantum dynamics of two coupled Schrödinger equations. Utilizing a matrix transformation analogous to the Darboux method we find analytic solutions valid in special cases, “quasiexact solutions.” The general conditions for matrix Darboux transformations are formulated. The method is applied to a special case of wave-packet dynamics.