Based on the matrix realignment and partial transpose, we develop an approach to the entangling power and operator entanglement of quantum unitary operators. We demonstrate the approach by studying several unitary operators on qudits, and indicate that these two matrix rearrangements are convenient to use in studying entangling capabilities of quantum operators.

We present a general method for distinguishing bipartite states by local operations and classical communication. It unifies several available methods together. This method is applicable for arbitrary bipartite states, i.e., it works not only for entangled states but also for separable states. We also study the local distinguishability for maximally entangled states which are in an arbitrary basis.

Periodic adiabatic rapid passage from counterpropagating light pulses is used in a parameter domain outside of the conventionally expected successful range to produce large optical forces on atoms by coherent control of the momentum exchange between the light and atoms. Both the magnitude and velocity range are much larger than those of the usual radiative force. We observed the force on metastable He atoms by the deflection of the atomic beam with periodic pulse sequences. We have also been able to map out the force magnitude in the two-dimensional parameter space of peak Rabi frequency and sweep range, and we find qualitative agreement with our model.

We observe the time evolution of ground-state ion alignment in a laser-produced plasma. Krypton ions produced in a strong, linearly polarized optical laser field $({10}^{14}–{10}^{15}\mathrm{W}∕{\mathrm{cm}}^2)$ are aligned along the field polarization axis. Using microfocused, tunable x rays from Argonne’s Advanced Photon Source, we measure orbital alignment as a function of time. For plasma densities of the order of ${10}^{14}{\mathrm{cm}}^{-3}$, the alignment decays within a few nanoseconds. A quantitative model explains the decay in terms of electron-ion collisions in the plasma. By applying an external magnetic field, we are able to suppress the disalignment and induce coherent spin precession of the Kr ions, thus providing an in situ monitor of magnetic fields in a plasma.

We present a significantly improved scheme of entanglement detection inspired by local uncertainty relations for a system consisting of two qubits. Developing the underlying idea of local uncertainty relations, namely correlations, we demonstrate that it is possible to define a measure which is invariant under local unitary transformations and which is based only on local measurements. It is quite simple to implement experimentally and it allows entanglement quantification in a certain range for mixed states and exactly for pure states, without first obtaining full knowledge (e.g., through tomography) of the state.

The influence of many-particle effects on the absolute values and the shape of doubly differential cross section of resonance inelastic scattering of a linearly polarized x-ray photon by the free Ar atom near $K$ and $K{M}_{23}$ ionization thresholds is studied theoretically. Shown is the evolution of spatially extended profile of the scattering cross section into the principal $K{\beta }_{1,3}$ and satellite $K{\beta }^V$ structures of the $\mathrm{Ar}K\beta$ emission spectrum. The calculations are performed in nonrelativistic Hartree-Fock approximation for the atomic wave functions and in the dipole approximation for the anomalous-dispersion scattering amplitude. The following many-particle effects are included: radial relaxation of electron shells, correlational loosening, vacuum correlations, spin-orbital, and multiplet splitting, configuration interaction in doubly excited atomic states, Auger and radiative decays for the vacancies produced. Calculations results are predictions while for the case of the incident photon energies of 3199.2 and $3245.9\mathrm{eV}$ they compare well with the results of the synchrotron experiment of Deslattes et al. [Phys. Rev. A 27, 923 (1983)] on measuring the x-ray $K\beta$ emission spectrum of the free Ar atom.

Low-energy electron-impact excitations of ${\mathrm{N}}_2$ molecules are studied using the fixed-bond $R$-matrix method based on state-averaged complete active-space self-consistent-field orbitals. Thirteen target electronic states of ${\mathrm{N}}_2$ are included in the model within a valence configuration interaction representation of the target states. Integrated as well as differential cross sections of the $A{}^3\Sigma _u^{+}$, $B{}^3\Pi _g$, $W{}^3\Delta _u$, $B^{\prime }{}^3\Sigma _u^{-}$, $a^{\prime }{}^1\Sigma _u^{-}$, $a{}^1\Pi _g$, $w{}^1\Delta _u$, and $C{}^3\Pi _u$ states are calculated and compared with the previous experimental measurements. These excitations, especially of the higher four states, have not been studied enough theoretically in the previous literature. In general, good agreements are observed both in the integrated and differential cross sections. However, some discrepancies are seen in the integrated cross sections of the $A^3{\Sigma }_u^{+}$ and $C{}^3\Pi _u$ states, especially around a peak structure.

We study spontaneous radiative decay of translational levels of an atom in the vicinity of a semi-infinite dielectric. We systematically derive the microscopic dynamical equations for the spontaneous decay process. We calculate analytically and numerically the radiative linewidths and the spontaneous transition rates for the translational levels. The roles of the interference between the emitted and reflected fields and of the transmission into the evanescent modes are clearly identified. Our numerical calculations for the silica-cesium interaction show that the radiative linewidths of the bound excited levels with large enough but not too large vibrational quantum numbers are moderately enhanced by the emission into the evanescent modes and those for the deep bound levels are substantially reduced by the surface-induced redshift of the transition frequency.

We investigate energy propagation in a perturbed optical lattice, studying the nonlinear adiabatic evolution of a light beam. Through an asymptotic model, we demonstrate that: (i) energy propagating in the adiabatic regime visualizes the dispersion relation of the unperturbed lattice; (ii) the adiabatic evolution can be broken by nonlinearity, giving rise to tunneling between Bloch bands; (iii) the tunneling is accompanied by nonlinear emission of one—or more—coherent Bloch waves, the properties of which can be completely controlled by linear and/or nonlinear parameters. We verify the analytical results against numerical simulations and indicate possible experimental implementations.

We present a generation condition for realizing high-$Q$ TM whispering-gallery modes (WGMs) in semiconductor microcylinders. For microcylinders with symmetry or weak asymmetry vertical waveguiding, we show that TM WGMs can have a high $Q$ factor, with the magnitude of ${10}^4$ at the radius of the microcylinder of $1\mathrm{\mu }\mathrm{m}$, by three-dimensional numerical simulation. The $Q$ factor of TE WGMs is much less than that of TM WGMs in the semiconductor microcylinders due to a vertical radiation loss caused by mode coupling with the vertical propagating mode. The results open up a possible application of TM WGMs in semiconductor microcylinders for efficient current injection microlasers and single photon sources.

The temporal output of a Ni-like Ag x-ray laser of wavelength $13.9\mathrm{nm}$ has been recorded using a streak camera with ultrashort $\left(700\mathrm{fs}\right)$ temporal resolution. We present a model to calculate the degree of coherence and Fourier transform limit of x-ray laser pulses produced by amplified spontaneous emission and relate the results from the model to previous interferometric measurements of the coherence length of the same Ni-like Ag x-ray laser and our measured duration of temporal output. Our modeling shows that the interferometer and streak camera results are consistent and close to the Fourier transform limit at longer gain medium lengths.

Quantum control of the four-wave mixing produced by two-color $\omega \text{−}3\omega$ femtosecond laser pulses propagating in a two-level system is accomplished by varying the relative phase between the two laser pulses. The phase sensitivity of the spectral $5\omega$ anti-Stokes component is cancelled when the ac Stark shift produced by the $\omega$ and $3\omega$ pulses is compensated. We apply perturbation theory and provide simple analytical formulas for the phase-sensitivity cancellation in the $5\omega$ anti-Stokes component. We demonstrate that this quantum interference effect is robust against chirping of the pulses and show that asymmetric chirping results in phase-sensitive shaping of the four-wave mixing spectra.

We study the problem of driving a known initial quantum state onto a known pure state without resorting to unitary transformations. This task can be achieved by means of a discrete sequence of von Neumann measurements only, introducing $N$ observables which are consecutively measured in order to make the state of the system approach the target state. We show that the probability of projecting onto the target state can be increased meaningfully by adding suitable observables to the process, that is, it converges to 1 when $N$ increases. These observables depend on the initial state and on the target state. We compare this scheme with one for which the initial state is not known [see L. Roa et al., Phys. Rev. A 73, 012322 (2006)]. This comparison shows that the knowledge of the initial density operator does not always increase the probability of success.

Both experiments and simulations have shown that the temperature of antihydrogen atoms $\left(\overline{\mathrm{H}}\right)$ formed in a strongly magnetized positron-antiproton plasma is mainly determined by the heavy particles’ temperature. A routine to keep cooling antiprotons $\left(\overline{p}\right)$ by using ultracold $(<1\mathrm{K})$ electrons is proposed under attainable experimental conditions. When cold positrons are loaded into such a low-temperature electron-antiproton mixture, ultracold antihydrogen atoms can be produced at a temperature below $\sim 1\mathrm{K}$. Our large-scale molecular-dynamics simulations, which involve $20000$ particles ($e^{-}$, $e^{+}$, and $\overline{p}$) evolving up to $1\mathrm{\mu }\mathrm{s}$, have confirmed the generation of trappable $\overline{\mathrm{H}}$ atoms.

The fidelity of postselecting devices based on direct photon number detection can be significantly improved by insertion of a phase-insensitive optical amplifier in front of the detector. The scheme is simple, and the cost to the probability of obtaining the appropriate detector outcome is low.

We have used an ultrafast laser pulse shaper in conjunction with a genetic algorithm to investigate dynamic alignment in room temperature CO. We find, in experiment and simulation, non-transform-limited laser pulse shapes that interact nonimpulsively with the molecules, yet are just as effective for transient alignment as shorter transform-limited pulses with the same energy. We use principal control analysis to determine which pulse characteristics, in experiment and simulation, are most important for the alignment control we observe. The analysis results suggest that in spite of the fact that the aligning laser intensities $(\sim {10}^{14}\mathrm{W}∕{\mathrm{cm}}^2)$ are sufficiently large to induce ionization, a simple rigid-rotor model with constant polarizabilities accurately describes the laser-driven molecular dynamics.

We investigate the effect of the position-dependent $s$-wave scattering length (SSL) on Bose-Einstein condensate (BEC) dynamics. In particular, we study the propagation of a BEC within a finite regime where the SSL, tuned by a periodic magnetic or optical field, results in the Bragg scattering of the BEC. We have predicted a matter-wave optical limiting process and bistability, which have potential applications like a matter wave limiter, a BEC mirror or cavity, and an atomic switch. The first phenomenon is a direct result of this periodic spatial tuning, showing that the position-dependent tuning of the SSL has the potential to result in novel properties of ultracold atomic gases.