We develop an entanglement measure by extending Jaeger’s Minkowskian norm entanglement measure. This measure can be applied to a much wider class of multipartite mixed states, although still “quasi” in the sense that it is still incapable of dividing precisely the sets of all separable and entangled states. As a quadratic scalar function of the system density matrix, the quasimeasure can be easily expressed in terms of the so-called coherence vector of the system density matrix, by which we show the basic properties of the quasimeasure including (1) zero entanglement for all separable states, (2) invariance under local unitary operations, and (3) nonincreasing under local positive operator-valued measure measurements. These results open up perspectives in further studies of dynamical problems in open systems, especially the dynamic evolution of entanglement, and the entanglement preservation against the environment-induced decoherence effects.

Au $L{\beta }_2$ satellites were investigated around the $L_1$ absorption edge with a high-resolution Johann-type spectrometer at the BL15XU undulator beamline SPring-8. The intensities of the $L{\beta }_2$ satellites were drastically changed at the threshold. Therefore, it is confirmed that the two visible satellites $L{\beta }_2^{\prime }$ and $L{\beta }_2^{″}$ are mainly attributed to the $L_1\text{−}{L}_3{M}_{4,5}$ Coster-Kronig transitions accompanied by the double-hole states of $L_3{M}_4$ or $L_3{M}_5$.

Iterative vibrational wave packet squeezing by a sequence of femtosecond pulses is proposed. Analytic formulas are derived for the harmonic oscillator case, and the practical implementation of the scheme is tested on different electronic transitions in ${\mathrm{Rb}}_2$.

Based on an experimental study of two-body and three-body collisions in ultracold strontium samples, a novel optical-sympathetic cooling method in isotopic mixtures is demonstrated. Without evaporative cooling, a phase-space density of $6\times {10}^{-2}$ is obtained with a high spatial density that should allow us to overcome the difficulties encountered so far to reach quantum degeneracy for Sr atoms.

The water dimer driven by strong infrared field is studied in the two-vibrational mode approximation. A pump pulse excites the OH vibrational modes and creates a coherent superposition of vibrational states of the low-frequency OO mode. The solution of the Schrödinger equation in the adiabatic approximation shows a strong sensitivity of the OO vibrational wave-packet dynamics to the absolute phase of the pump field. This effect appears due to a break down of the rotating-wave approximation when the Rabi frequency of the OH vibrational transition approaches the frequency of the OH mode. The violation of the rotating wave approximation modifies considerably the interaction of the probe radiation with the laser-driven molecule.

We calculate entropy-temperature curves for interacting bosons in unit filled optical lattices for both homogeneous and harmonically trapped situations, and use them to understand how adiabatic changes in the lattice depth affect the temperature of the system. In a translationally invariant lattice, the zero tunneling limit facilitates a rather detailed analytic description. Unlike the noninteracting bosonic system which is always cooled upon adiabatic loading for low enough initial temperature, the change in the excitation spectrum induced by interactions can lead to heating. Finite tunneling helps to reduce this heating. Finally, we study the spatially inhomogeneous system confined in a parabolic potential and show that the presence of the trap can significantly reduce the final available temperature, due to the nonvanishing superfluid component at the edge of the cloud which is present in trapped systems.

We construct a projection measurement process for the maximally entangled $N$-photon state [the NOON state $(\mid N,0⟩+\mid 0,N⟩)∕\sqrt{2}$] with only linear optical elements and photodetectors. This measurement process will give null result for any $N$-photon state that is orthogonal to the NOON state. We examine the projection process in more detail for $N=4$ by applying it to a four-photon state from type-II parametric down-conversion. This demonstrates an orthogonal projection measurement with a null result. This null result corresponds to a dip in a generalized Hong-Ou-Mandel interferometer for four photons. We find that the depth of the dip in this arrangement can be used to distinguish a genuine entangled four-photon state from two separate pairs of photons. We next apply the NOON state projection measurement to a four-photon superposition state from two perpendicularly oriented type-I parametric down-conversion processes. A successful NOON state projection is demonstrated with the appearance of the four-photon de Broglie wavelength in the interference fringe pattern.

By investigating the convex property of the function $R$, which appeared when computing the entanglement of formation for isotropic states [Phys. Rev. Lett. 85, 2625 (2000)] and in a tight lower bound of entanglement of formation for arbitrary bipartite mixed states [Phys. Rev. Lett. 95, 210501 (2005)], we show analytically that the results in these papers are valid not only for dimensions two and three but for any dimensions.

A series of metastable states below the $t\mu \left(2s\right)+d$ threshold have been discovered. The structure of the metastable $dt{\mu }_{J\nu }$ ion is studied here by the related suitable wave function and using the variational method. Few resonance energies and the related widths for $dt{\mu }_{J\nu }$ molecular states located below the $2s$ threshold are determined. For precise assessment of the reliability of the given wave function, the resonance formation rate is also calculated for the states which take place in the Vesman region. The obtained results are close to those previously reported and give strong indications that the related wave function is good enough to be useful for further calculations.

We describe how to control the temporal shape of adiabaton using peculiarities of propagation dynamics under coherent population trapping. Temporal compression is demonstrated as a special case of pulse shaping. The general case of unequal oscillator strengths of two optical transitions in an atom is considered.

In a recent paper, Szmytkowski proposed zero-range potentials for Dirac particles in three space dimensions. On the other hand, there is a theorem, proved by Svendsen a long time ago, which implies that zero-range potentials cannot be defined for the Dirac equation in two and three space dimensions. We discuss a difficulty that underlies Szmytkowski’s approach.

We disprove the critique of our recent work [R. Szmytkowski, Phys. Rev. A 71, 052708 (2005)] contained in the Comment by Coutinho and Nogami [Phys. Rev. A 73, 026701 (2006)]. We show that the model of zero-range potentials for scattering processes involving Dirac particles, proposed by us in the aforementioned work, admits a definition of a scalar product under which the plane-wave excited scattering wave function is normalizable to the Dirac delta function in the momentum space. In addition, we prove that the eigenchannel wave functions, introduced in the aforementioned paper, are orthogonal with respect to that scalar product.

The random switching of measurement bases is commonly assumed to be a necessary step of quantum key distribution protocols. In this paper we present a no-switching protocol and show that switching is not required for coherent-state continuous-variable quantum key distribution. Further, this protocol achieves higher information rates and a simpler experimental setup compared to previous protocols that rely on switching. We propose an optimal eavesdropping attack against this protocol, assuming individual Gaussian attacks. Finally, we investigate and compare the no-switching protocol applied to the original Bennett-Brassard 1984 scheme.

We present results of first-principles calculations of the frequency-dependent polarizabilities of all alkali-metal atoms for light in the wavelength range 300–1600 nm, with particular attention to wavelengths of common infrared lasers. We parametrize our results so that they can be extended accurately to arbitrary wavelengths above 800 nm. This work is motivated by recent experiments involving simultaneous optical trapping of two different alkali-metal species. Our data can be used to predict the oscillation frequencies of optically trapped atoms, and particularly the ratios of frequencies of different species held in the same trap. We identify wavelengths at which two different alkali-metal atoms have the same oscillation frequency.

We have measured the energies of several rotational branches of the $(0,0)$ band of the $EF$ ${}^1\Sigma _g^{+}\leftarrow X{}^1\Sigma _g^{+}$ transition in molecular hydrogen by use of Doppler-free two-photon laser excitation at $202\mathrm{nm}$. The accuracy for all three stable isotopic variations is 8 parts in ${10}^9$, nominally a fourfold improvement over previously available results, but some of the transition energies differ from previous work by as much as three standard deviations. The improved accuracy derives principally from our ability to measure the optical phase evolution of nanosecond laser pulses, then to predict quantitatively the line shapes of multiphoton transitions excited by them. The results allow comparably accurate determinations of the $EF$ state term energies, which in turn help to calibrate the entire excited-state spectrum of this fundamental molecular system. These improved calibrations are particularly useful to recent and ongoing efforts to determine the dissociation energy and ionization potential with improved accuracy.

New high-resolution experimental results on Ne $1s$ near-threshold photoionization with subsequent decay into a $2p^4\left({}^{1}D_2\right)n^{\prime }p$ or $2p^4\left({}^{1}D_2\right){\epsilon }^{\prime }p$ state are presented. The population of Rydberg states up to $n^{\prime }=12$ is determined as a function of excess energy. These data allow one to track in detail the transition from resonant Auger decay going along with shake-up of the spectator electron to shake-down and photoionization with recapture of the photoelectron. Results are in good agreement with a time-dependent quantum mechanical theory of Auger decay in the presence of a slow photoelectron.

For the interactions between a $\mathrm{He}\left(2{}^{3}S\right)$ atom and a $\mathrm{He}\left(2{}^{3}P\right)$ atom for like isotopes, we report perturbation theoretic calculations using accurate variational wave functions in Hylleraas coordinates of the coefficients determining the potential energies at large internuclear separations. We evaluate the coefficient $C_3$ of the first order resonant dipole-dipole energy and the van der Waals coefficients $C_6$, $C_8$, and $C_{10}$ for the second order energies arising from the mutual perturbations of instantaneous electric dipole, quadrupole, and octupole interactions. We also evaluate the leading contribution to the third-order energy. We establish definitive values including treatment of the finite nuclear mass for the ${}^3\mathrm{He}\left(2{}^{3}S\right)\text{−}{}^3\mathrm{He}\left(2{}^{3}P\right)$ and ${}^4\mathrm{He}\left(2{}^{3}S\right)\text{−}{}^4\mathrm{He}\left(2{}^{3}P\right)$ interactions.

We have numerically investigated ionization of molecules exposed to circularly polarized (CP) intense few-cycle pulses (FCPs) by solving the three-dimensional time-dependent Schrödinger equation. The resulting photoelectron spectra exhibit an interesting “plateau” feature that does not appear for atoms exposed to circularly-polarized laser fields. The origin comes from the intense CP field ionizing a portion of the electron wave packet about one nuclear center and driving it through the other. Moreover, the angular distribution of photoelectrons gives an indication of the carrier-envelope phase of the applied FCP, which implies that steering of photoelectrons in space can be achieved by controlling the FCP phase.