Alice and Bob share a correlated composite quantum system $AB$. If $AB$ is used as the key for a one-time pad cryptographic system, we show that the maximum amount of information that Alice can send securely to Bob is the quantum mutual information of $AB$.

We give a description of the continuous-variable teleportation protocol in terms of the characteristic functions of the quantum states involved. The Braunstein-Kimble protocol is written for an unbalanced homodyne measurement and arbitrary input and resource states. We show that the output of the protocol is a superposition between the input one-mode field and a classical one induced by measurement and classical communication. We choose to describe the input state distortion through teleportation by the average photon number of the measurement-induced field. Only in the case of symmetric Gaussian resource states we find a relation between the optimal added noise and the minimal EPR correlations used to define inseparability.

Using monochromatized synchrotron light and the ion time-of-flight method to detect the singly and doubly charged sodium and potassium ions, we have investigated the relative double-photoionization cross-section ratios of Na from $52.4\text{to}150\mathrm{eV}$ and of K from $36.5\text{to}170\mathrm{eV}$. We found that both followed a scaling law previously observed for Li and Be, which describes the photon energy dependence of that ratio and allows one to estimate its absolute value. We have also obtained the relative single- and double-photoionization cross sections for Na and K.

The times taken by positive muons $\left({\mu }^{+}\right)$ to slow down from initial energies in the range $\sim 3$ to $1\mathrm{MeV}$, to the energy of the last muonium formation, $\approx 10\mathrm{eV}$, at the end of cyclic charge exchange, have been measured in the pure gases ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, $\mathrm{Ar}$, and in the gas mixtures $\mathrm{Ar}\text{−}\mathrm{He}$, $\mathrm{Ar}\text{−}\mathrm{Ne}$, $\mathrm{Ar}\text{−}{\mathrm{CF}}_4$, ${\mathrm{H}}_2\text{−}\mathrm{He}$, and ${\mathrm{H}}_2\text{−}{\mathrm{SF}}_6$, by the muon spin rotation $\left(\mu \mathrm{SR}\right)$ technique. At $1\mathrm{atm}$ pressure, these slowing-down times, ${\tau }_{\mathrm{SD}}$, in $\mathrm{Ar}$ and ${\mathrm{N}}_2$, vary from $\sim 14\mathrm{ns}$ at the highest initial energies of $2.8\mathrm{MeV}$ to $6.5\mathrm{ns}$ at $1.6\mathrm{MeV}$, with much longer times, $\sim 34\mathrm{ns}$, seen at this energy in ${\mathrm{H}}_2$. Similar variations are seen in the gas mixtures, depending also on the total charge and nature of the mixture and consistent with well-established (Bragg) additivity rules. The times ${\tau }_{\mathrm{SD}}$ could also be used to determine the stopping powers, $dE∕dx$, of the positive muon in ${\mathrm{N}}_2$, $\mathrm{Ar}$, and ${\mathrm{H}}_2$, at kinetic energies near $2\mathrm{MeV}$. The results demonstrate that the ${\mu }^{+}$ and proton have the same stopping power at the same projectile velocity, as expected from the historic Bethe-Bloch formula, but not previously shown experimentally to our knowledge for the muon in gases at these energies. The energy of the first neutralization collision forming muonium (hydrogen), which initiates a series of charge-exchanging collisions, is also calculated for $\mathrm{He}$, $\mathrm{Ne}$, and $\mathrm{Ar}$. The formalism necessary to describe the stopping power and moderation times, for either muon or proton, in three energy regimes—the Bethe-Bloch, cyclic charge exchange, and thermalization regimes—is developed and discussed in comparison with the experimental measurements reported here, and elsewhere. The slowing-down times through the first two regimes are controlled by the relevant ionization and charge-exchange cross sections, whereas the final thermalization regime is most sensitive to the forwardness of the elastic scattering cross sections. In this regime the slowing-down times (to $kT$) at nominal pressures are expected to be $\lesssim 100\mathrm{ns}$.

We report on a fully relativistic close-coupling (CC) calculation of the electron impact excitation (EIE) of $\mathrm{Ne}\mathrm{IX}$. The multiconfiguration Dirac-Fock (MCDF) method was used in a calculation of $\mathrm{Ne}\mathrm{IX}$ atomic structure. The EIE calculation of $\mathrm{Ne}\mathrm{IX}$ was carried out using the Dirac $R$-matrix method and the MCDF orbitals for principal quantum number $n\le 5$ with target states up to $n=5$ corresponding to $49\mathrm{CC}$ (49 target states in the CC expansion). The EIE calculation included both resonance and channel coupling effects. We demonstrate that strong resonances appear in the excitation of the highly charged ion $\mathrm{Ne}\mathrm{IX}$, in particular for intercombination and forbidden transitions. Compared to less highly charged He-like ions, we show that for $\mathrm{Ne}\mathrm{IX}$ all $N$-shell and $O$-shell levels start to give rise to Rydberg resonant states dipping just below $M$-shell and $N$-shell target thresholds, respectively. In comparison with previous calculations carried out with either the close-coupling or the distorted wave method, our calculations show significant differences with respect to cross sections and effective collision strengths. The important $\mathrm{Ne}\mathrm{IX}$ line intensity $G$ ratio $(G=(i+f)∕r)=[\mathrm{forbidden}+\mathrm{intercombination}]∕\mathrm{resonance})$ calculated based on our MCDF and Dirac $R$-matrix results is in good agreement with the existing accurate EBIT measurements. This calculation has direct applications to laboratory measurements and observations of astrophysical x-ray sources.

We present a many-body formalism for BCS-BEC crossover, which represents a modification of the Bardeen-Cooper-Schrieffer-Leggett ground state to include four-fermion and higher correlations. In the Bose-Einstein condensate regime, we show how our approach contains the four-fermion behavior of Petrov et al. and associated scattering length $a_{dd}$ at short distances and, second, reduces to composite-boson Bogoliubov physics at long distances. It reproduces the Lee-Yang term, whose numerical value is also fixed by $a_{dd}$. We have also examined the next term beyond the Lee-Yang correction in a phenomenological fashion, building on cloud size data and collective mode experiments, although one has to view this phenomenological analysis with some caution since experiments are in a state of flux and are performed close to unitarity.

We show a way to realize an arbitrary rotation gate in a three-level superconducting quantum interference device (SQUID) qubit using resonant interaction. In this approach, the two logical states of the qubit are represented by the two lowest levels of the SQUID and a higher-energy intermediate level is utilized for the gate manipulation. By considering spontaneous decay from the intermediate level during the gate operation, we present a formula for calculating average fidelity over all possible initial states. Finally, based on realistic system parameters, we show that an arbitrary rotation gate can be achieved with a high fidelity in a SQUID.

A soft-x-ray laser amplifier based on plasma solid target with a weak transverse refraction and a large gain zone is numerically investigated. A two-dimensional hydrodynamic code ARWEN with radiation transport solved by multigroup method based on adaptive mesh refinement has been used to describe the spatial and temporal plasma evolution. An iron target is transiently pumped creating gain on the $J=0-1$ neonlike transition at $\lambda =25.5\mathrm{nm}$. We show that using a super-Gaussian, instead of Gaussian, transverse spatial laser driver profile leads to a reduction of the transverse refraction by two orders of magnitude and to an enlargement of the gain zone surface by about a factor of 2.

We report a high-resolution spectroscopic study of molecular ions at millikelvin temperatures. We measured several rovibrational infrared transitions in $\mathrm{H}{\mathrm{D}}^{+}$ molecular ions, stored in a radio-frequency trap and sympathetically cooled to $\approx 20\mathrm{mK}$ by laser-cooled ${\mathrm{Be}}^{+}$ ions. We observed hyperfine splitting of the lines, in good agreement with theoretical predictions. The transitions were detected by monitoring the decrease in ion number after selective photodissociation of $\mathrm{H}{\mathrm{D}}^{+}$ ions in the upper vibrational state. The method described here is expected to be generally applicable.

A Hookean model of a three-body problem for particles with arbitrary masses and charges where two of them interact with each other through a Coulomb potential and with the third through a harmonic potential is presented. It is shown that a condition relating the masses to the harmonic coupling constants must be satisfied in order to render this problem separable. A general exact analytic solution written in terms of the relative interparticle coordinates is given as well as general expressions for the total and binding energies of this three-body system. We apply these results to examine electronic, muonic, antiprotonic, and pionic families of non-Born-Oppenheimer Hookean systems. The first contains the atoms or atomic ions: ${\mathrm{Ps}}^{-}\left(e^{+}{e}^{-}{e}^{-}\right)$, ${\mathrm{H}}^{-}\left(p^{+}{e}^{-}{e}^{-}\right)$, ${\mathrm{D}}^{-}\left(d^{+}{e}^{-}{e}^{-}\right)$, ${\mathrm{T}}^{-}\left(p^{+}{e}^{-}{e}^{-}\right)$, ${}^4\mathrm{He}\left(h{e}^{+2}{e}^{-}{e}^{-}\right)$, and the following molecular ions: ${\mathrm{Ps}}_2^{+}\left(e^{-}{e}^{+}{e}^{+}\right)$, ${\mathrm{H}}_2^{+}\left(e^{-}{p}^{+}{p}^{+}\right)$, $\mathrm{H}{\mathrm{D}}^{+}\left(e^{-}{d}^{+}{p}^{+}\right)$, ${\mathrm{HT}}^{+}\left(e^{-}{t}^{+}{p}^{+}\right)$, ${\mathrm{DT}}^{+}\left(e^{-}{d}^{+}{t}^{+}\right)$, ${\mathrm{D}}_2^{+}\left(e^{-}{d}^{+}{d}^{+}\right)$, ${\mathrm{T}}_2^{+}\left(e^{-}{t}^{+}{t}^{+}\right)$. The muonic and antiprotonic families are similar to the electronic ones except that the species are formed replacing $e^{-}$ by ${\mu }^{-}$ or $p^{-}$. The pionic family comprises exotic atoms containing at least one pion. We also apply these results to two-electron three-dimensional spherical quantum dots and for these systems we examine the effect of electronic correlation, particularly on the singlet-triplet transitions and on the collective motion of the electrons and center of mass leading to “floppy”dynamics.

The structure, energetics, electronic, and optical properties of the organic molecule, diindenoperylene (DIP), are investigated by first-principles density-functional and time-dependent density-functional theory. The photoabsorption cross section, computed on the optimized geometry within the linear response theory, gives results in good agreement with experimental data, with minor differences ascribed to vibrational levels and to solvent effects. Ab initio dynamical simulations of the molecular triplet excited state show that DIP is stable against distortions, at least on the picosecond time scale. The theoretical approach, involving a combination of first-principles techniques, is shown to be able to describe in detail the response properties of low-dimensional organic semiconductor systems, currently important in nanotechnological applications.

Oscillations in integral elastic cross sections for collision energies in range ${10}^{-4}–1\mathrm{eV}$ are a general feature appearing in many atomic collision systems. We illustrate its generality by proton scattering on multielectron atoms such as He, Ne, and Ar atoms. Expressing the sum over partial waves in the integral cross section in terms of the Mulholland identity and calculating all contributions to the formula we show that the Regge oscillations are a quantum-mechanical feature of the cross sections, the other features being of quasiclassical nature.

A recent pump-probe experiment employing tunable, linearly polarized x rays demonstrated that ${\mathrm{Kr}}^{+}$ ions produced via strong-field ionization in a linearly polarized laser field are aligned, but that the degree of alignment is greatly overestimated by nonrelativistic strong-field ionization models. An effective one-electron model of strong-field ionization is presented that includes the effect of spin-orbit interaction. The method makes use of a flexible finite-element basis set and determines ionization rates in this square-integrable basis using a complex absorbing potential. It is found that even at the electric-field strength corresponding to the saturation intensity for the ionization of Kr, there is very little mixing between the $4p_{3∕2}$ and $4p_{1∕2}$ outer-valence orbitals. This shows that the uncoupled $m_l,m_s$ projection quantum numbers are inappropriate to describe the ${\mathrm{Kr}}^{+}$ states that are populated by strong-field ionization of krypton. For the x-ray probe step, a description is developed, within a density-matrix formalism. It is demonstrated that the inclusion of spin-orbit interaction in the ionization process provides satisfactory agreement with the experimental observation. Possibilities for time-resolved studies utilizing fs and sub-fs laser pulses are indicated.

We show that the vibrational state tailoring method developed for molecular systems can be applied for cold atoms in optical lattices. The original method is based on a three-level model interacting with two strong laser pulses in a counterintuitive sequence [M. Rodriguez et al., Phys. Rev. A 62, 053413 (2000)]. Here we outline the conditions for achieving similar dynamics with single time-dependent potential surfaces. It is shown that guided switching between diabatic and adiabatic evolution has an essential role in this system. We also show that efficient and precise tailoring of motional states in optical lattices can be achieved, for instance, simply by superimposing two lattices and moving them with respect to each other.

We theoretically investigate properties of magnetostatic traps for cold atoms that are subject to externally applied uniform fields. We show that Ioffe-Pritchard traps and other stationary points of $B$ are confined to a two-dimensional curved surface, or manifold $\mathcal{M}$, defined by $\det (\partial B_i∕\partial x_j)=0$. We describe how stationary points can be moved over the manifold by applying external uniform fields. The manifold also plays an important role in the behavior of points of zero field. Field zeroes occur in two distinct types, in separate regions of space divided by the manifold. Pairs of zeroes of opposite type can be created or annihilated on the manifold. Finally, we give examples of the manifold for cases of practical interest.

We present an analytical and numerical analysis of neutron multilevel interference phenomena generated when a neutron passes through a series of $N$ resonant coils operated at the successive conditions $\hslash ({\omega }_0+n\Delta \omega )=2{\mu }_n(B_0+n\Delta B)$ with $n=0,1,\dots ,N-1$. Each coil produces spin flip with probability $\rho$ between 0 and 1; thus the number of waves for the neutron is doubled after each coil, finally giving $2^N$ interfering neutron waves. The phase difference between any pair is a multiple of a time dependent “phase quantum” $\Delta \Phi \left(t\right)$. The analysis predicts for each number $N$ a highly regular pattern for the quantum mechanical probability to find the neutron spin in one specific state as a function of $\rho$ and $\Delta \Phi$. These patterns evolve in time and show revivals after a time $T$ determined by the step $\Delta \omega$ according to $T=2\pi ∕\Delta \omega$. For some adjustments of the system an analytical solution is obtained. Application of multilevel interference in high-resolution neutron modulated-intensity-by-zero-effort–type spectrometers is discussed.

A formally exact expression for the interaction density response function $\chi (\mathbf{r},{\mathbf{r}}^{\prime },\omega )$ exists in terms of (i) its noninteracting counterpart ${\chi }_0(\mathbf{r},{\mathbf{r}}^{\prime },\omega )$ and (ii) an exchange $\left(x\right)$-correlation $\left(c\right)$ kernel $f_{xc}(\mathbf{r},{\mathbf{r}}^{\prime },\omega )$. In the absence of a first-principles theory for the $\omega$ dependence of $f_{xc}$, the adiabatic approximation is most frequently made in this term, to construct a workable time-dependent density-functional theory. In the present study, a proposal is put forward to avoid the adiabatic approximation by working in the exchange-only limit in which $f_{xc}$ is set equal to $f_x(\mathbf{r},{\mathbf{r}}^{\prime },\omega )$. We then refer to a result for the exchange energy given by Pines and Nozieres to motivate the assumption that $f_x=f_x\left[\mathrm{Im}{\chi }_0(\mathbf{r},{\mathbf{r}}^{\prime },\omega )\right]$. The essential proposal here is therefore that the integral equation to be solved for the interacting density response function $\chi$ is in the exchange-only case characterized entirely by the noninteracting response function ${\chi }_0$.

It has been proposed recently that hyperfine depolarization of selected molecular rotational states can be used to produce molecules with highly polarized nuclear spins, and formulas for two distinct nuclei have been given in the limit of hierarchical approximation. Here we present the general, nonhierarchical coupling formalism for the derivation of the $H_{\left[i\right]}^{\left(k\right)}(I,t)$ factors that govern the time dependence of the nuclear polarizations. The described technique, especially when combined with methods that polarize the electronic angular momentum, can lead to the production of highly polarized atoms from molecular photodissociation, at densities close to that of the parent molecule. In addition, we calculate the time dependence of the H and F nuclear spin polarizations, following the pulsed-laser preparation of the HF $(v=1,J=1,m=1)$ state. It is shown that the polarization of the F and H nuclear spins attain values of about 85% and 70% at time delays of about $1\mathrm{\mu }\mathrm{s}$ and $4\mathrm{\mu }\mathrm{s}$, respectively. Similar results are shown for the pulsed preparation of the DF $(v=0,J=1,m=1)$ state, demonstrating the D atoms can also be significantly polarized.

Total destruction cross sections for negative aluminum clusters $\mathrm{Al}^{-}{}_n$ with $n=2–4$, and total detachment cross sections of the aluminum anion ${\mathrm{Al}}^{-}$, incident on Ar are measured. These values, and previously measured cross sections of $\mathrm{C}^{-}{}_n$ and $\mathrm{Si}^{-}{}_n$ with $n=1–4$, are compared with total (elastic plus inelastic) cross sections for electron impact on the same target. Similarities between the experimental cross sections for anions and electrons, observed in the velocity range of $0.2\text{to}1.8\mathrm{a.u.}$, led to a model in which the overall shape of the dependence on velocity of the anionic cross sections is well described by a convolution of the anion’s outermost electron momentum distribution with the free electron-impact cross sections, and their absolute values obtained by fitting a cluster-size dependent additive constant. A geometrical interpretation is then proposed.

An apparatus combining the cross-beam and threshold-ionization techniques has been used to measure absolute cross sections for electron impact dissociation of ${\mathrm{CH}}_4$ molecules into the ${\mathrm{CH}}_3$ neutral radicals at energies from threshold up to $13\mathrm{eV}$. The threshold energy for the lowest-lying ${}^{3}T_2$ state has been observed to be $7.5\pm 0.3\mathrm{eV}$, and attributed to neutral ${\mathrm{CH}}_3$ formation. Peaks have been observed at $\sim 9.6$ and $11.5\mathrm{eV}$, in agreement with electronic excitation and photon impact neutral dissociation literature data. The current results indicate that all excited states of ${\mathrm{CH}}_4$ predominantly result in dissociation via the ${\mathrm{CH}}_3$ neutral radical channel below $12.5\mathrm{eV}$.