It is customary to describe the transport of neutrons through capillary guides in terms of ray optics, thus entirely neglecting interference effects. We show that such an approach becomes physically inconsistent as soon as it is applied to typical transportation distances reported experimentally. A consistent inclusion of wave aspects within the paraxial approximation predicts a dynamical behavior incompatible with geometrical optics. In particular, the observation of self-images in neutron pipes with circular or rectangular profile may represent an unambiguous means to demonstrate the relevance of waveguide-internal diffraction phenomena.

Unambiguous discrimination is a strategy to the discrimination problem that identifies the state with certainty, leaving a possibility of undecidability. This paper points out that the optimal success probability of unambiguous discrimination is mathematically the well-known semidefinite programming problem. A family of lower bounds of the optimal success probability is also given.

We obtain a tight bound on the measurement which discriminates without error between two nonorthogonal states. The derivation is based on the no-signaling condition, without any reference to generalized measurements.

Physical systems, characterized by an ensemble of interacting constituents, can be represented and studied by different algebras of operators (observables). For example, a fully polarized electronic system can be studied by means of the algebra generated by the usual fermionic creation and annihilation operators or by the algebra of Pauli (spin-1/2) operators. The Jordan-Wigner isomorphism gives the correspondence between the two algebras. As we previously noted, similar isomorphisms enable one to represent any physical system in a quantum computer. In this paper we evolve and exploit this fundamental observation to simulate generic physical phenomena by quantum networks. We give quantum circuits useful for the efficient evaluation of the physical properties (e.g., the spectrum of observables or relevant correlation functions) of an arbitrary system with Hamiltonian H.

We have developed a method for calculating the rates for three-body recombination of cold atoms. This method allows us to treat not only zero total angular momentum, $J=0,$ states but also $J>\mathrm{}0\mathrm{}$ states, so that recombinations at nonzero collision energies can be considered. Our method is applied to ground-state helium atoms ${}^4\mathrm{He},$ using a realistic interaction potential. In addition, we obtain the rates for collision induced dissociation.

We investigate the phenomenon of quantum radiation–i.e., the conversion of (virtual) quantum fluctuations into (real) particles induced by dynamical external conditions–for an initial thermal equilibrium state. For a resonantly vibrating cavity a rather strong enhancement of the number of generated particles (the dynamical Casimir effect) at finite temperatures is observed. Furthermore we derive the temperature corrections to the energy radiated by a single moving mirror and an oscillating bubble within a dielectric medium as well as the number of created particles within the Friedmann-Robertson-Walker universe. Possible implications and the relevance for experimental tests are addressed.

An optimal universal cloning transformation is derived that produces M copies of an unknown qubit from a pair of orthogonal qubits. For $M>\mathrm{}6,$ the corresponding cloning fidelity is higher than that of the optimal copying of a pair of identical qubits. It is shown that this cloning transformation can be implemented probabilistically via parametric down conversion by feeding the signal and idler modes of a nonlinear crystal with orthogonally polarized photons.

Coding using quantum states in an angular-momentum $\mathrm{}(2j+1)\mathrm{}$-dimensional Hilbert space H is considered in this paper. A concatenated code is studied in two steps. In the first step the space $H^N$ is considered and the code is its subspace $H_A$ spanned by the direct products of N angular-momentum states with the same m. In the second step the space $H_A^M$ is considered and the code is its subspace $H_B$ spanned by the direct products of M angle states with the same m. It is shown that the code introduces redundancy with respect to any transformation.

A notion of strength of an unextendible product basis is introduced and a quantitative measure for it is suggested with a view to providing an indirect measure for the bound entanglement of formation of the bound entangled mixed state associated with an unextendible product basis.

Relativistic four-component electronic structure calculations including the nuclear spin-independent parity-odd $(P$-odd) electroweak neutral current are presented for the study of the breaking of mirror symmetry in the vibrational structure of chiral molecules. The structures of all four chiral CFXYZ compounds $(X,Y,Z=\mathrm{H},\mathrm{Cl},\mathrm{Br},\mathrm{I})$ were optimized by coupled cluster techniques with a subsequent normal-mode analysis. Vibrational wave functions for the C-F stretching mode along the normal coordinate were produced numerically from calculated coupled cluster potential-energy curves that yield the following left-right parity-violating differences in frequency for the C-F stretching fundamental transitions: 1.7 mHz for CHFClBr, 11.6 mHz for CFClBrI, 23.7 mHz for CHFClI, and 50.8 mHz for CHFBrI. In order to measure these differences in the spectra of the two enantiomers of these chiral molecules, a two orders of magnitude improvement in the resolution of current precision optical spectroscopy is required.

Intense L x rays have been observed in $\sim 2-\mathrm{k}\mathrm{e}\mathrm{V}/\mathrm{u}\hspace{0.5em}{\mathrm{Kr}}^{q+}$ $(q=27\mathrm{}–33)$ ions colliding with various atom and molecule targets. These x rays are understood to originate from electron capture processes into high-Rydberg states of the projectile ion from the outermost shell of target where the captured electron cascades down into the vacant L shell of the ion, thus emitting L x rays. It has been found that the observed L x-ray spectra move toward higher energy as the ion charge (q) increases. The observed L x-ray spectra are compared with synthetic spectra using various models. It has been found that the L x-ray production cross sections obtained for ${\mathrm{Kr}}^{27+}$ ions are inversely proportional to the ionization energy of target, similar to those recently observed in K x rays produced from ions with K-shell vacancy, and correspond to roughly 40% of total electron capture cross sections, meanwhile the rest of the electron cascades into the metastable states and thus cannot decay within a viewing region of a Si(Li) x-ray detector.

Three-step laser excitation is employed to measure the ${}^2{F}_{5/2}{-}^2{F}_{7/2}$ fine-structure splittings in seven $n{}^{2}F$ manifolds of Rb for $4<~n<~10.$ The use of cycling transitions in the excitation process intensifies the spectra and simplifies signal detection. This sequence of seven measured splittings should serve as a useful test of fine-structure calculations in heavy alkali-metal atoms where complicated, noncentral field treatments of core polarization, configuration mixing, electron correlation, and/or relativistic effects are generally required.

Torsion-vibration energy structures deduced from the ${\nu }_7$ ${(A}^{\prime }$ ${\mathrm{CH}}_3$ in-plane rocking mode), ${\nu }_8$ ${(A}^{\prime }$ CO stretching mode), ${\nu }_{11}$ ${(A}^{″}$ ${\mathrm{CH}}_3$ out-of-plane rocking mode), $2{\nu }_7,$ $2{\nu }_8,$ ${\nu }_7+{\nu }_8,$ and ${\nu }_8+{\nu }_{11}$ fundamental, overtone, and combination bands of ${\mathrm{CH}}_3\mathrm{OH}$ are compared and contrasted to that of the ground vibrational state. The $2{\nu }_7$ in-plane ${\mathrm{CH}}_3$-rocking overtone and the ${\nu }_8+{\nu }_{11}$ CO-stretching and out-of-plane rocking combination bands are identified in the high-resolution Fourier transform spectrum, and point to systematic trends in the excited-state torsional behavior for methanol. Torsion-vibration substate origins have been determined for the eight modes considered, and fitted to a five-parameter Fourier model to characterize the energy patterns. Excitation of the ${\nu }_8$ mode has little influence on the torsional structure, but the A-E torsional energy splittings are sharply reduced with excitation of ${\nu }_7$ and inverted with excitation of ${\nu }_{11}.$ These changes are examined from the perspective of a recent torsion-vibration interaction model for states of degenerate E vibrational parentage [J. T. Hougen, J. Mol. Spectrosc. 207, 60 (2001)]; the $K=0\mathrm{}$ substate energy pattern for ${\nu }_7$ and ${\nu }_{11}$ supports Hougen’s model but with some differences in detail. The values of the K-scaling parameter ρ determining the periodicity of the torsional energies appear to vary almost linearly with the number of quanta of vibrational excitation. The changes are suggestive of substantial zero-point effects on the axial moments of inertia, with implications for the structural determination of the ${\mathrm{CH}}_3$ methyl top.

The interaction between the center of mass (c.m.) and internal degrees of freedom plays a crucial role for the properties and behavior of moving negative ions in magnetic fields. A promising theoretical approach, including this interaction to describe field-induced anions, has been developed very recently. The theory is aimed at weak to moderate magnetic field strengths and therefore of immediate relevance to laboratory experiments. In the present work, we apply this approach to study the classical dynamics of the anions in magnetic fields. We focus on features of the bound motion of anions and on the analysis of the anions’ autodetachment induced by the c.m. motion.

Theoretical results from multistate semirelativistic Breit-Pauli R-matrix calculations and two first-order distorted-wave calculations are presented for electron-impact excitation of krypton from the ${(4p}^{5}5s)$ $J=0,2\mathrm{}$ metastable states to the ${(4p}^{5}5s)$ and ${(4p}^{5}5p)$ manifolds. Except for a few cases, in which the method to account for relativistic effects becomes surprisingly critical, fair overall agreement between the predictions from the various theoretical models is achieved for intermediate and high energies. However, significant discrepancies remain with the few available experimental data.

Fission of doubly charged metal clusters is studied using the open-shell two-center deformed jellium Hartree-Fock model and local density approximation. Results of calculations of the electronic structure and fission barriers for the symmetric and asymmetric channels associated with the following processes ${\mathrm{Na}}_{10}^{2+}\to {\mathrm{Na}}_7^{+}+{\mathrm{Na}}_3^{+},$ ${\mathrm{Na}}_{18}^{2+}\to {\mathrm{Na}}_{15}^{+}+{\mathrm{Na}}_3^{+}$ and ${\mathrm{Na}}_{18}^{2+}\to 2{\mathrm{Na}}_9^{+}$ are presented. The role of the exact exchange and many-body correlation effects in metal clusters fission is analyzed. It is demonstrated that the influence of many-electron correlation effects on the height of the fission barrier is more profound if the barrier arises nearby or beyond the scission point. The importance of cluster deformation effects in the fission process is elucidated with the use of the overlapping-spheroids shape parametrization allowing one an independent variation of deformations in the parent and daughter clusters.

A systematic investigation of the equilibrium geometries, nature of bonding, and stability has been carried out for Sn-doped Li clusters, Li${}_n$Sn, $(1\mathrm{}<~n<~9),$ by employing ab initio density-functional molecular dynamics. The ${\mathrm{Li}}_4\mathrm{Sn}$ cluster with strong ionic bonds is found to be the most stable. The systematics of the energetics and charge density indicates a change in the nature of bonding from ionic to delocalized metalliclike, after $n=6.\mathrm{}$ The impurity atom, viz., Sn, is seen to induce significant changes in the geometries of host ${\mathrm{Li}}_n$ clusters. Sn does not get trapped and has a maximum of sixfold coordination with Li atoms. By carrying out finite-temperature isokinetic simulations for ${\mathrm{Li}}_6\mathrm{Sn}$ and ${\mathrm{Li}}_7$ at two temperatures, $100$ and $300\mathrm{K},$ we demonstrate a rather dramatic change in the low-temperature behavior of the Sn-doped Li cluster.

We develop practical formulas for the calculation of the matrix elements of the interaction of the electromagnetic field with an atomic state, beyond the long-wavelength approximation. The atom-plus-field Hamiltonian is chosen to have the multipolar form, containing the electric, paramagnetic, and diamagnetic operators. The final workable expressions include the interactions to all orders and are derived by first expanding the fields in partial waves. The electric-field operator reaches a constant value as the radial variable becomes large, contrary to the result of the electric-dipole approximation (EDA) where the value of the corresponding operator increases indefinitely. Applications are given for Rydberg states of hydrogen up to $n=50\mathrm{}$ and for free-free transitions in a Coulomb potential. Such matrix elements are relevant to a number of real and virtual processes occurring during laser-atom interactions. The computation is done numerically, using a combination of analytic with numerical techniques. By comparing the results of the EDA with those of the exact treatment, it is shown that the former is inadequate in such cases. This finding has repercussions on the theory and understanding of the physics of quantum systems in high-lying Rydberg levels and wave packets or in scattering states.