Secure communication requires message authentication. In this paper we address the problem of how to authenticate quantum information sent through a quantum channel between two communicating parties with the minimum amount of resources. Specifically, our objective is to determine whether one elementary quantum message (a qubit) can be authenticated with a key of minimum length. We show that, unlike the case of classical-message quantum authentication, this is not possible.

Dielectronic recombination of Ba from a continuum of finite bandwidth in microwave fields of 4, 8, and 12 GHz exhibits a resonant enhancement when the microwave frequency matches a $\Delta n=1,$ 2, or 3 transition in the intermediate autoionizing $n\mathcal{l}$ Rydberg states. The origin of the enhancement is resonant Stark mixing of high- and low-l states of different n. Surprisingly, there is little difference between linear and circular polarization of the microwave field, which is attributed to the fact that more than two n levels are coupled in both cases. The dependence of the widths of the resonances on the microwave field is related to how many n states are coupled, and the threshold field for the appearance of the resonances is due to the requirement that low-l states with nonzero quantum defects be mixed with the hydrogenic high-l states. Finally, recombination has been observed from energies in excess of the ${\mathrm{Ba}}^{+}$ ${6p}_{1/2}$ limit.

We investigate the limitations arising from atomic collisions on the storage and delay times of probe pulses in electromagnetically induced transparency experiments. We find that the atomic collisions can be described by an effective decay rate that limits storage and delay times. We calculate the momentum and temperature dependence of the decay rate and find that it is necessary to excite atoms at a particular momentum depending on temperature and spacing of the energy levels involved in order to minimize the decoherence effects of atomic collisions.

DOI: 10.1103/Phys Rev A. 61. 022725

In recent papers we have discussed the meaning of dressed excited quantum states. We have shown that these states can be formulated in terms of distribution functions outside the Hilbert space. Our approach applies to “nonintegrable” systems in the sense of Poincaré. It involves the analytic continuation of the unitary operator U describing the transformation from bare to dressed stable states. This leads to a “star-unitary” operator $\Lambda .$ Interacting fields are nonintegrable systems obtained as a result of resonances. It is therefore natural to expect that our previous results remain valid for interacting fields. We consider a simple example, which corresponds to an extension of the usual Friedrichs model. This involves a local field in interaction with a bilocal scalar field. This model has been previously studied by one of the co-authors (I.P.). It is a simplified version of the model describing $\overrightarrow{A}B+C$ transition with quadratic interaction. The usual Bogoliubov transformation eliminates the field corresponding to A, while our method leads to strictly exponential decay of unstable field. The dressed field A corresponds to a singular distribution function outside the Liouville-Hilbert space. As in the Friedrichs model there exists two time scales—one for the preparation of a dressed state and depending on initial conditions called “Zeno period” and the other universal for the decay.

We show that the resolution “per absorbed particle” of standard absorption tomography can be outperformed by a simple interferometric setup, provided that the different levels of “gray” in the sample are not uniformly distributed. The technique hinges upon the quantum Zeno effect and has been tested in numerical simulations. The scheme we propose could be implemented in experiments with uv light, neutrons, or x rays.

We have calculated the atomic electric dipole moments (EDMs) induced in ${}^{199}\mathrm{Hg},$ ${}^{129}\mathrm{Xe},$ ${}^{223}\mathrm{Rn},$ ${}^{225}\mathrm{Ra},$ and ${}^{239}\mathrm{Pu}$ by their respective nuclear Schiff moments S. The results are [in units ${10}^{-17}S\left(e{\mathrm{fm}}^3{)}^{-1}e\mathrm{cm}\right]:$ ${d(}^{199}\mathrm{Hg})=-2.8,$ ${d(}^{129}\mathrm{Xe})=0.38,$ ${d(}^{223}\mathrm{Rn})=3.3,$ ${d(}^{225}\mathrm{Ra})=-8.5,$ and ${d(}^{239}\mathrm{Pu})=-11.$ We have also calculated corrections to the parity- and time-invariance-violating $(P,T$-odd) spin-axis interaction constant in TlF. These results are important for the interpretation of atomic and molecular experiments on EDMs in terms of fundamental $P,T$-odd parameters.

The classic example of the destruction of interference fringes in a “which-way” experiment, caused by an environmental interaction, may be viewed as the destruction of first-order coherence as defined by Glauber many years ago [Phys. Rev. 130, 2529 (1963); 131, 2766 (1963)]. However, the influence of an environment can also destroy the $n$th-order quantum coherence in a quantum system, where this high order coherence is captured. We refer to this phenomenon as the nth-order decoherence. In this paper we show that, just as the first-order coherence can be understood as the interference of the amplitudes for two distinct paths, the higher order coherence may be understood as the interference of multiple amplitudes corresponding to multiple paths. To see this, we introduce the concept of $n$th-order “multiparticle wave amplitude.” It turns out that the $n$th-order correlation function can be expressed as the square norm of some multiparticle wave amplitude for the closed system or as the sum of such square norms for the open system. We also examine, as a specific example, how an environment can destroy the second-order coherence by eliminating the interference between various multiple paths.

There are Hamiltonians that solve the search problem of finding one of N items in $O\left(\sqrt{N}\right)$ steps. These are Hamiltonians describing an oscillation between two states. In this paper we propose a generalized search Hamiltonian $H_g.$ Then the known search Hamiltonians become special cases of $H_g.$ For the generalized search Hamiltonian, we present the remarkable result that searching with 100% success is subject only to the phase factor in $H_g$ and independent of the number of states or initialization.

We use a magneto-optical trap to isolate ${}^{84}\mathrm{Kr}$ atoms in the metastable ${}^3{P}_2$ state and then measure the rate of 125.0-nm fluorescence due to spontaneous magnetic quadrupole $\mathrm{}\left(M2\mathrm{}\right)\mathrm{}$ decay. We normalize the overall fluorescence rate from the sample using a “quenching” process in which laser excitation provides a path for prompt decay to the ground state, with each atom emitting one 123.6-nm photon. A single, solar-blind photomultiplier tube is used to detect both the $M2\mathrm{}$ and the quench-induced photons, so that only small corrections relating to spectral response are necessary. We find a spontaneous decay rate of $\Gamma =0.0354\mathrm{}\left(22\right)\mathrm{}{\mathrm{s}}^{-1},$ which translates into a lifetime of 28.3(1.8) s. This result is discussed in the context of previous measurements and calculations of ${}^3{P}_2$ lifetimes in the rare gases.

Potential curves for $\mathrm{Hg}\mathrm{}\left(6s6p\right)+\mathrm{Hg}\mathrm{}\left(6s6p\right)\mathrm{}$ are calculated in the $\Lambda S$ representation and transformed to the spin-orbit representation using empirical spin-orbit coupling constants. With these potential curves, total chemi-ionization cross sections are estimated using a black-sphere approximation for the short-range interaction. Long-range barriers, found in some of the potential curves, reduce the thermal-energy cross sections. Because these barrier heights are rather uncertain, the cross sections are also calculated with their suppression. The result, for $\mathrm{Hg}{(}^3{P}_1)+\mathrm{Hg}{(}^3{P}_0)$ collisions at 300 K, of $30–125\hspace{0.5em}{\AA }^2,$ overlaps the range of experimental measurements. For the only other pair considered in previous experiments, $\mathrm{Hg}{(}^3{P}_0)+\mathrm{Hg}{(}^3{P}_0),$ chemi-ionization was found to be energetically allowed but dynamically improbable. An upper limit, already lower than the posited measured value, was established, and the actual cross section is expected to be considerably smaller; this finding provides additional evidence that the reactants were misidentified in the experiment. The cross section for the statistically dominant metastable atoms $\mathrm{Hg}{(}^3{P}_2)+\mathrm{Hg}{(}^3{P}_2),$ $8–11\hspace{0.5em}{\AA }^2,$ is also relatively small. The chemi-ionization cross sections obtained for the other triplet reactants are $33–80\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^3{P}_1)+\mathrm{Hg}{(}^3{P}_1),$ $17–31\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^3{P}_2)+\mathrm{Hg}{(}^3{P}_0),$ and $15–22\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^3{P}_2)+\mathrm{Hg}{(}^3{P}_1).\mathrm{}$ The chemi-ionization cross sections for the singlet atom are large, $116–226\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^1{P}_1)+\mathrm{Hg}{(}^3{P}_0),$ $161–285\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^1{P}_1)+\mathrm{Hg}{(}^3{P}_1),$ $105–293\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^1{P}_1)+\mathrm{Hg}{(}^3{P}_2),$ and $132–397\hspace{0.5em}{\AA }^2$ for $\mathrm{Hg}{(}^1{P}_1)+\mathrm{Hg}{(}^1{P}_1).\mathrm{}$ Though we do not yet have the autoionization widths required for quantitative distinction, the relative shapes of the neutral and ion potential curves suggest that most of the chemi-ionization will be of the associative, instead of the Penning type, even when the latter is energetically allowed.

A formulation of the time-dependent close-coupling theory is described which allows efficient calculation of the total ionization cross section for many electron energies. The Fourier transform method is applied to the electron-impact ionization of ${\mathrm{Li}}^{2+}$ and excellent agreement is found with experiment and a distorted-wave method.

We present results from measurements of $L\alpha$ x-ray production cross sections of the elements W, Pt, and Au by impact of electrons with energies in the range 10–30 keV. The cross sections were obtained by measuring $L\alpha$ x-ray intensities emitted from very thin films of the studied elements deposited on thick carbon substrates. The directional and energy spreading of the electron beam within the active film and the x-ray enhancement due to electron backscattering from the substrate were accounted for by means of Monte Carlo simulation. Recorded x-ray intensities were converted to absolute x-ray production cross sections by using two different methods; the first employs measured values of the sample thickness and the number of incident electrons and estimated detector efficiencies; the second is based on a comparison between measured and calculated bremsstrahlung intensities. Experimental data are compared with the results of simple analytical formulas of common use in practical electron probe microanalysis, with calculated cross sections obtained from the distorted-wave Born approximation and with other experimental data available in the literature.

In this work, a theoretical study on electron-CF collisions in the low- and intermediate-energy range is reported. More specifically, calculated elastic differential, integral, and momentum-transfer cross sections as well as grand total (elastic and inelastic) and absorption cross sections are presented in the (1–500)-eV energy range. A complex optical potential is used to represent the electron-molecule interaction dynamics, while the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. Comparison of the present results with existing experimental and theoretical data for electron collisions with NO (an isoelectronic molecule of CF) is made.

We present experimental results concerning an isocharge study of multielectronic capture and stabilization in slow collisions of ${\mathrm{Ar}}^{16+},$ ${\mathrm{Xe}}^{16+},$ ${\mathrm{Kr}}^{16+}$ with ${\mathrm{C}}_{60}.$ Partial multicapture cross sections ${\sigma }_r^s$ are given for all observed channels. The core effect only has an effect when the number of transferred electrons is sufficiently high. In this case, the stabilization ratio has been found equal to 4.2, 3.6, and 2.9 for ${\mathrm{Ar}}^{16+},$ ${\mathrm{Kr}}^{16+},$ and ${\mathrm{Xe}}^{16+},$ respectively. These measurements are qualitatively explained by fewer steps in the autoionization cascades for Xe than for Ar.

A free-electron-like model is first shown to lead to the eigenvalue sum of the π electrons in almost spherical C cages, being proportional to N, where N is the number of C atoms. The model is also closely related to a tight-binding model, stemming from the Hückel theory of π electrons. The equilibrium radius $R_e$ of the C cages is assumed to be determined by the “rule” of constant surface area per C atom, and hence $R_e\propto N^{1/2}.$ We then compare these models with a series of Hartree-Fock calculations on the fullerenes ${\mathrm{C}}_{50},$ ${\mathrm{C}}_{60},$ ${\mathrm{C}}_{70},$ and ${\mathrm{C}}_{84},$ from which more accurate energy scaling relations are obtained. Finally, the relation between the total energy of the four C cages at equilibrium and the all-electron eigenvalue sum is confirmed by the Hartree-Fock studies.

We analyze the resonant cavity enhancement of a hollow “optical bottle beam” for the dipole-force trapping of dark-field-seeking species. We first improve upon the basic bottle beam by adding further Laguerre-Gaussian components to deepen the confining potential. Each of these components itself corresponds to a superposition of transverse cavity modes, which are then enhanced simultaneously in a confocal cavity to produce a deep optical trap needing only a modest incident power. The response of the trapping field to displacement of the cavity mirrors offers an unusual form of mechanical amplifier in which the Gouy phase shift produces an optical Vernier scale between the Laguerre-Gaussian beam components.

The interaction of atoms, molecules, crystals, and nanotubes with time-periodic laser fields can lead to high-order dynamical symmetries (DS’s). Here we employ group theoretical methods to study the DS-related properties (quantum numbers, nonaccidental degeneracies) of quantum systems possessing high-order DS’s. As explicit examples we take finite-order rotation symmetry in point and plane groups, and a circularly polarized laser field. We find that nonaccidental degeneracies induced by spatial and time-reversal symmetries may not be lifted inside the laser field. A general result of this work is that the time-evolution operator needs to be computed only up to $1/N$ [or, even, $1/\left(2N\right)\mathrm{}]$ of the optical cycle, where N is the order of the DS. This allows a substantial reduction of the computational effort required for studying the time-dependent dynamics of such systems.

We present an improved many-body T-matrix theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. The resulting mean-field theory is valid in arbitrary dimensions and able to describe the low-temperature crossover between three-, two-, and one-dimensional Bose gases. When applied to a degenerate two-dimensional atomic hydrogen gas, we obtain a reduction of the three-body recombination rate, which compares favorably with experiment. Supplementing the mean-field theory with a renormalization-group approach to treat the critical fluctuations, we also incorporate into the theory the Kosterlitz-Thouless transition that occurs in a homogeneous Bose gas in two dimensions. In particular, we calculate the critical conditions for the Kosterlitz-Thouless phase transition as a function of the microscopic parameters of the theory. The proposed theory is further applied to a trapped one-dimensional Bose gas, where we find good agreement with exact numerical results obtained by solving a nonlinear Langevin field equation.

The vortex-vortex interaction in two-component Bose-Einstein condensates is shown to present characteristic effects not possible in single-component condensates. In particular, vortices in different components undergo separate, but concentric, orbits for both the same and opposite circulation. In addition, contrary to the well-known behavior in single-component condensates, vortices with the same circulation created in the less dense component merge in the presence of dissipation, allowing for the creation of metastable vortices with more than one quantum of circulation.