We propose a practical and versatile technique to achieve completely field-free molecular orientation with an intense, nonresonant, two-color laser field with a slow turn on and rapid turn off. The technique is based on the combined effects of both anisotropic polarizability interaction and anisotropic hyperpolarizability interaction. Using a FCN molecule as a sample, we show that the orientation achieved adiabatically by the peak of the laser pulse can be successfully revived at the rotational period of the molecule with the same degree of orientation. The crucial importance of the sufficiently slow turn on of the laser pulse is emphasized to achieve the highest possible degree of orientation.

We present a protocol for deterministically generating an optimal two-mode-squeezed state of distant free-space atomic ensembles. The protocol relies on two passes of a single coherent pulse through two separate atomic ensembles placed in homogeneous magnetic fields. In contrast to previous single-pass schemes, our approach significantly enhances the degree of entanglement due to the exponential behavior of the Einstein-Podolsky-Rosen variance. We also provide an efficient scheme to perform Bell measurement of atomic states, enabling the implementation of high-fidelity atomic quantum teleportation.

In a two-qubit system the coupling with an environment considerably affects the entanglement dynamics, usually leads to the loss of entanglement within a finite time. Since entanglement is a key feature in the application of such systems to quantum information processing, it is highly desirable to find a way to prolonging its lifetime. We present a simple model of an interacting two-qubit system in the presence of a thermal Markovian environment. The qubits are modeled as interacting spin-$1∕2$ particles in a magnetic field and the environment is limited to inducing single spin-flip events. A simple scheme allows us to calculate the relaxation rates for all processes. We show that the relaxation dynamics of the most entangled state exhibit critical slowing down as a function of the magnetic field, where the relaxation rate changes from exponentially small values to finite values in the zero-temperature limit. We study the effect of temperature and magnetic field on all the other relaxation rates and find that they exhibit unusual properties, such as nonmonotonic dependence on temperature and a discontinuity as a function of magnetic field. In addition, a simple scheme to include non-Markovian effects is presented and applied to the two-qubit model. We find that the relaxation rates exhibit a sharp, cusplike resonant structure as a function of the environment memory time, and that for long memory times all the different relaxation rates merge into a single one.

A polarization analysis of the fine-structure intervals for the $n=17$ Rydberg states of Mg and the $n=29$ states of ${\mathrm{Si}}^{2+}$ is performed. The coefficients of all terms in the polarization expansion up to $r^{-8}$ were computed using a semiempirical single electron analysis combined with the relativistic all-order single-double method (MBPT-SD) which includes all single-double excitations from the Dirac-Fock wave functions to all orders of perturbation theory. The revised analysis yields dipole polarizabilities of ${\alpha }_1=35.04\left(3\right)\mathrm{a.u.}$ for ${\mathrm{Mg}}^{+}$ and ${\alpha }_1=7.433\left(25\right)\mathrm{a.u.}$ for ${\mathrm{Si}}^{3+}$, values only marginally larger than those obtained in a previous analysis [E. L. Snow and S. R. Lundeen, Phys. Rev. A 75, 062512 (2007); E. L. Snow and S. R. Lundeen, Phys. Rev. A77, 052501 (2008)]. The polarizabilities are used to make estimates of the multiplet strength for the resonant transition for both ions. The revised analysis did see significant changes in the slopes of the polarization plots. The dipole polarizabilities from the MBPT-SD calculation, namely $35.05\left(12\right)\mathrm{a.u.}$ and $7.419\left(16\right)\mathrm{a.u.}$, are within 0.3% of the revised experimental values.

Elastic electron scattering off the lithium dimer in the ${}^{2}A_g$ symmetry is studied. $R$-matrix calculations in the fixed-nuclei approximation are presented for a set of internuclear separations as well as energies of the stable negative ion. The aim of this work is to study effects of the polarization taken into account in the outer region on the elastic scattering cross sections. This work is the first part of a larger project dealing with ${\mathrm{Li}}_2$ leading to calculations of nonelastic processes like vibrational excitation and dissociative electron attachment.

We report on the observation of five Feshbach resonances in collisions between ultracold ${}^7\mathrm{Li}$ and ${}^{87}\mathrm{Rb}$ atoms in the absolute ground-state mixture where both species are in their $\mid f,m_f⟩=\mid 1,1⟩$ hyperfine states. The resonances appear as trap losses for the ${}^7\mathrm{Li}$ cloud induced by inelastic heteronuclear three-body collisions. The magnetic field values where they occur are important quantities for an accurate determination of the interspecies interaction potentials. Results of coupled channels calculations based on the observed resonances are presented and refined potential parameters are given. A very broad Feshbach resonance centered around $649\mathrm{G}$ should allow for fine-tuning of the interaction strength in future experiments.

Boson droplets (i.e., dense assemblies of bosons at low temperature) are shown to mask a significant amount of single-particle behavior and to manifest collective, droplet-wide excitations. To investigate the balance between single-particle and collective behavior, solutions to the wave equation for a finite size Bose system are constructed in the limit where the ratio $\epsilon$ of the average nearest-neighbor boson distance to the size of the droplet or the wavelength of density disturbances is small. In this limit, the lowest order wave function varies smoothly across the system, i.e., is devoid of structure on the scale of the average nearest-neighbor distance. The amplitude of short range structure in the wave function is shown to vanish as a power of $\epsilon$ when the interatomic forces are relatively weak. However, there is residual short range structure that increases with the strength of interatomic forces. While the multiscale approach is applied to boson droplets, the methodology is applicable to any finite size Bose system and is shown to be more direct than field theoretic methods. Conclusions for ${}^4\mathrm{He}$ nanodroplets are drawn.

We investigate a two-species Fermi gas with a large mass ratio interacting by an interspecies short-range interaction. Using the Born-Oppenheimer approximation, we determine the interaction energy of two heavy fermions immersed in the Fermi sea of light fermions as a function of the $s$-wave scattering length. In the BCS limit, we recover the perturbative calculation of the effective interaction between heavy fermions. The $p$-wave projection of the effective interaction is attractive in the BCS limit while it turns out to be repulsive near the unitarity limit. We find that the $p$-wave attraction reaches its maximum between the BCS and unitarity limits, where the maximal $p$-wave pairing of heavy minority fermions is expected. We also investigate the case where the heavy fermions are confined in two dimensions and the $p$-wave attraction between them is found to be stronger than that in three dimensions.

We develop a general scheme for detecting spin correlations inside a two-component lattice gas of bosonic atoms, stimulated by the recent theoretical and experimental advances on analogous systems for a single component quantum gas. Within a linearized theory for the transmission spectra of the cavity mode field, different magnetic phases of a two-component (spin $1∕2$) lattice bosons become clearly distinguishable. In the Mott-insulating (MI) state with unit filling for the two-component lattice bosons, three different phases: antiferromagnetic, ferromagnetic, and the $XY$ phases are found to be associated with drastically different cavity photon numbers. Our suggested study can be straightforwardly implemented with current cold atom experiments.

The light force on particles trapped in the field of a high-$Q$ cavity mode depends on the quantum state of field and particle. Different photon numbers generate different optical potentials and different motional states induce different field evolution. Even for negligible internal particle excitation, which yields linear polarizability, the quantum character of particle motion generates nonlinear field dynamics. We derive a corresponding effective field Hamiltonian containing all the powers of the photon number operator, which predicts nonlinear phase shifts and squeezing even at the few-photon level. Simulations of the full particle-field dynamics confirm this and show significant particle-field entanglement.

The Cherenkov radiation is substantially modified in the presence of a medium with a nontrivial dispersion relation. We consider Cherenkov emission spectra of a point or line charge, respectively, moving in general, three- (3D) and two-dimensional (2D) photonic crystals. Exact analytical expressions for the spectral distribution of the radiated power are obtained in terms of the Bloch mode expansion. The resulting expression reduces to a simple contour integral (3D case) or a one-dimensional sum (2D case) over a small fraction of the reciprocal space, which is defined by the generalized Cherenkov condition. We apply our method to a specific case of a line source moving with different velocities in a 2D square-lattice photonic crystal. Our method demonstrates a reasonable agreement with numerically rigorous finite-difference time-domain calculations while being less demanding on computational resources.

The chaotic ray dynamics inside dielectric cavities is described by the properties of an invariant chaotic saddle. The localization of the far-field emission in specific directions, recently observed in different experiments and wave simulations, is found to be a consequence of the filamentary pattern of the saddle’s unstable manifold. For cavities with mixed phase space, the chaotic saddle is divided in hyperbolic and nonhyperbolic components, related, respectively, to the intermediate exponential $(t<t_c)$ and the asymptotic power-law $(t>t_c)$ decay of the energy inside the cavity. The alignment of the manifolds of the two components of the saddle explains why even if the energy concentration inside the cavity dramatically changes from $t<t_c$ to $t>t_c$, the far-field emission changes only slightly. Simulations in the annular billiard confirm and illustrate the main results.

We study the possibility of giving a classical interpretation to quantum projective measurements for a particle described by a pure Gaussian state whose Wigner function is non-negative. We analyze the case of a projective measurement which gives rise to a proper Wigner function—i.e., taking on, as its values, the eigenvalues of the projector. We find that, despite having this property, this kind of projector produces a state whose Wigner function ceases to be non-negative and hence precludes its interpretation as a classical probability density. We also study the general case in which the projected state has a non-negative Wigner function, but then we find that the Wigner function of the projector is not a proper one. Thus, we conclude that a non-negative Wigner function is inadequate to serve as a hidden-variable model for quantum processes in which projective measurements take place.

We theoretically show that according to the disentanglement behavior under a composite noise environment, the Hilbert space of a two-qubit system can be divided into two separate parts: a three-dimensional subspace in which all states disentangle asymptotically, and the rest in which all states disentangle abruptly. The violation of additivity for entanglement decay rates under weak noises [Phys. Rev. Lett. 97, 140403 (2006)] can be explained using such Hilbert-space division.

We report on the excitation of single molecules via narrow zero-phonon transitions using short laser pulses. By monitoring the Stokes-shifted fluorescence, we studied the excited state population as a function of the delay time, laser intensity, and frequency detuning. A $\pi$-pulse excitation was demonstrated with merely 500 photons, and 5 Rabi cycles were achieved at higher excitation powers. Our findings are in good agreement with theoretical calculations and provide a first step toward coherent manipulation of the electronic states of single molecules with few photons.

Shenvi, Kempe, and Whaley’s quantum random-walk search (SKW) algorithm [Phys. Rev. A 67, 052307 (2003)] is known to require $O\left(\sqrt{N}\right)$ number of oracle queries to find the marked element, where $N$ is the size of the search space. The overall time complexity of the SKW algorithm differs from the best achievable on a quantum computer only by a constant factor. We present improvements to the SKW algorithm which yield a significant increase in success probability, and an improvement on query complexity such that the theoretical limit of a search algorithm succeeding with probability close to one is reached. We point out which improvement can be applied if there is more than one marked element to find.

A scheme to generate shared tripartite entangled states, with two-trapped atoms in a cavity held by Alice (qubits $A_1$ and $A_2$) entangled to a single-trapped atom in a remote laboratory owned by Bob $\left(B\right)$, is proposed. The entanglement is generated through interaction of trapped atoms with two-mode squeezed light shared by the two cavities. The proposed scheme is an extension of the proposal of Son et al. [J. Mod. Opt. 49, 1739 (2002)], where the possibility of entangling two remote qubits using a bipartite continuous variable state was examined. While the global negativity detects the free entanglement of the three atom mixed state, the bound entanglement is detected by the negativity calculated from pure state decomposition of the state operator. The partial negativities calculated by selective partial transposition of the three atom mixed state detect the pairwise entanglement of qubit pairs $A_{1}B$, $A_{2}B$, and $A_1{A}_2$. The entanglement of three atoms is found to be $W$-like, no Greenberger-Horne-Zeilinger-like quantum correlations being generated.

We obtain the shielding of the nuclear magnetic moment by an electron in the $n{s}_{1∕2}$ state in a hydrogenlike ion with arbitrary nuclear charge $Z$. The calculation is based on the decomposition of the shielding correction into two terms corresponding to the intermediate states with $j=1∕2$ and $3∕2$. The former is evaluated using the $j=1∕2$ projection of the correction to the electron wave function due to the external magnetic field, while the latter is calculated by applying the $j=3∕2$ projection of the correction to the wave function due to the hyperfine interaction between the electron and the nucleus.

The Lippmann-Schwinger (LS) equation for the $K$ matrix is numerically solved for the collision of $\mathrm{H}{\mathrm{D}}^{+}+e$ interacting by the configuration interaction (CI). The realistic CI strength is deduced from ab initio calculation of electron scattering. The LS equation is extended to the negative collision energies in the context of multichannel quantum defect theory (MQDT) for the dissociative recombination (DR). A decoupling property is shown for the LS equation, which is useful for reducing the amount of the calculation. The Chebyshev quadrature is employed for the calculation and a fully converged result has been obtained. Using the result with the MQDT, the DR cross section of $\mathrm{H}{\mathrm{D}}^{+}$ is obtained. It has turned out that the off-the-energy-shell contribution is indispensable for understanding the DR. The contribution from the negative energies largely affects the low-energy DR. The DR at low energy is induced by the indirect process with rotational excitation. The separable approximation on the CI is examined for the realistic CI strength. This approximation has turned out to be inadequate for the DR of $\mathrm{H}{\mathrm{D}}^{+}$. The calculated rate coefficient reproduces the experiment [A. Al-Khalili et al., J. Phys. A 68, 042702 (2003)] both on the absolute magnitude and resonance structure. The off-the-energy shell contribution largely affects on the initial vibrational state $\left(v^{+}\right)$ dependence. This contribution increases the rate coefficient for $v^{+}=0$ and decreases for $v^{+}=2$.