We consider the transfer of a two-species Bose-Einstein condensate (BEC) into an optical lattice with a density such that a Mott-insulator state with one atom per species per lattice site is obtained in a deep lattice regime. Depending on collisional and transition parameters, the result could be either a “mixed” or a “separated” Mott-insulator phase. Such a mixed two-species insulator would be well suited for the formation of dipolar molecules via photoassociation. The resulting array of dipolar molecules could then be used for the formation of a dipolar molecular condensate or for computation. For the case of a ${}^{87}\mathrm{Rb}{-}^{41}\mathrm{K}$ two-species BEC, however, the large interspecies scattering length makes it difficult to obtain the desired mixed Mott-insulator phase. To overcome this difficulty, we investigate the effect of varying the lattice frequency on the mean-field interaction and propose a favorable parameter regime, under which a lattice of dipolar molecules could be generated.

We have experimentally studied the optical bistable behavior in an optical ring cavity filled with a collection of three-level $\Lambda$-type rubidium atoms, interacting with two collinearly propagating laser beams. The bistability so observed is very sensitive to the induced atomic coherence in this electromagnetically induced transparency system or consequently to the altered nonlinearity in the system and, thus, can easily be controlled by changing the intensity and the frequency detuning of the coupling field.

We present a methodology that allows recording the coherence length of photons emitted by a single quantum system in a solid. The feasibility of this approach is experimentally demonstrated by measuring the self-interference of photons from the zero-phonon line emission of a single nitrogen-vacancy defect in diamond at 1.6 K. The first-order correlation function has been recorded and analyzed in terms of a single exponential decay time. A coherence time of $\sim 5\mathrm{ps}$ has been obtained, which is in good agreement with the corresponding spectral line width and demonstrates the feasibility of the Fourier-transform spectroscopy with single photons.

We present an explicit construction of entanglement witnesses for depolarized states in an arbitrary finite dimension. For an infinite dimension, we generalize the construction to twin beams perturbed by Gaussian noises in the phase and in the amplitude of the field. We show that entanglement detection for all these families of states require only three local measurements. The explicit form of the corresponding set of local observables needed for an entanglement witness is derived.

We present a scheme to achieve maximally entangled states, controlled phase-shift gate, and SWAP gate for two superconducting-quantum-interference-device (SQUID) qubits, by placing SQUIDs in a microwave cavity. We also show how to transfer quantum information from one SQUID qubit to another. In this scheme, no transfer of quantum information between the SQUIDs and the cavity is required, the cavity field is only virtually excited and thus the requirement on the quality factor of the cavity is greatly relaxed.

We present a general theoretical framework for both deterministic and probabilistic entanglement transformations of bipartite pure states achieved via local operations and classical communication. This framework unifies and greatly simplifies previous works. A necessary condition for “pure contraction” transformations is given. Finally, constructive protocols to achieve both probabilistic and deterministic entanglement transformations are presented.

Energies, transition rates, and electron electric-dipole-moment (EDM) enhancement factors are calculated for low-lying states of Ce IV and Pr V using relativistic many-body perturbation theory. This study is related to recent investigations of the more complicated Gd IV ion, which is promising for electron EDM experiments. The ions Ce IV and Pr V both have a single valence electron, permitting one to carry out reliable ab initio calculations of energy levels, transition rates, and other atomic properties using well-developed computational methods.

We have measured the photoabsorption spectra of the Kr-like ions ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$ at photon energies corresponding to the excitation of $4s-\mathrm{np}$ resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in $4s$-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra.

We report the results of a fully ab initio study of resonant vibrational excitation of ${\mathrm{CO}}_2$ by electron impact via the 3.8 eV ${}^2{\Pi }_u$ shape resonance. First, we solve the fixed-nuclei, electronic scattering problem using the complex Kohn variational method to produce resonance parameters for both the ${}^2{A}_1$ and ${}^2{B}_1$ components of the resonance for a variety of symmetric-stretch geometries and for a range of bending angles. The nuclear dynamics associated with the two components of the resonance are coupled by Renner-Teller coupling. We carry out a two-mode treatment of the nuclear dynamics in a complex local potential model using the complex resonance energy surfaces derived from our calculated fixed-nuclei cross sections with Renner-Teller coupling.

The hyperspherical $\mathcal{R}$-matrix method with semiclassical outgoing waves is used to study the direct double photoionization (DPI) of the valence shell of the lightest alkaline earth-metal Be. The absolute fully integrated, singly, doubly, and triply differential cross sections obtained are compared with the single set of measurements available and with recent calculations based on the convergent close coupling and time-dependent close coupling methods. The level of agreement between all these data is very encouraging. A comparison is also made between the DPI of He and the direct DPI of the valence shell of Be. It confirms that the electron-electron correlations are stronger in the valence $2s$ shell of Be than in the $1s$ shell of He, thus contributing to a desirable clarification.

Electron-stimulated desorption of positive ions from supported Na nanoclusters has been investigated in terms of the localization or delocalization of valence holes, as well as the reaction of Na with the substrate or coadsorbed molecules. On the Ar substrate, the ${\mathrm{Na}}^{+}$ yield is enhanced markedly at the smallest coverage and decay steeply with increasing coverage. We interpret that ${\mathrm{Na}}^{+}$ is emitted via Coulomb explosion of the adsorbed Na nanoclusters in which valence holes are confined, i.e., localized. Very few ${\mathrm{Na}}^{+}$ ions are emitted from the Na nanoclusters adsorbed on the Pt(111) and ${\mathrm{H}}_2\mathrm{O}$ substrates. The complete suppression of the ${\mathrm{Na}}^{+}$ emission is interpreted as a result of neutralization of nanoclusters due to electron transfer from the substrate, i.e., the delocalization of valence holes. Na tends to interact with the ${\mathrm{H}}_2\mathrm{O}$ nanoclusters on the Ar substrate as revealed from the evolution of hydrated ${\mathrm{Na}}^{+}$ ions prior to bare ${\mathrm{Na}}^{+}$ ions. The formation of Na nanoclusters is suppressed on the ${\mathrm{SF}}_6$ substrate due to reactions, resulting in a much smaller ${\mathrm{Na}}^{+}$ yield than that from the Ar substrate.

The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde $\left({\mathrm{H}}_2\mathrm{CO}\right)$ and deuterated ammonia $\left({\mathrm{ND}}_3\right).\mathrm{}$ With ${\mathrm{H}}_2\mathrm{CO}$ a continuous flux is measured of $\approx {10}^9/\mathrm{s}$ and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.

Bosons in the form of ultracold alkali-metal atoms can be confined to a one-dimensional (1D) domain by the use of harmonic traps. This motivates the study of the ground-state occupations ${\lambda }_i$ of effective single-particle states ${\phi }_i,$ in the theoretical 1D impenetrable Bose gas. Both the system on a circle and the harmonically trapped system are considered. The ${\lambda }_i$ and ${\phi }_i$ are the eigenvalues and eigenfunctions, respectively, of the one-body density matrix. We present a detailed numerical and analytic study of this problem. Our main results are the explicit scaled forms of the density matrices, from which it is deduced that for fixed i the occupations ${\lambda }_i$ are asymptotically proportional to $\sqrt{N}$ in both the circular and harmonically trapped cases.

Assuming that the scattering length properly describes the interaction, and taking into account the lowest-order correction effects to the strong mean-field interaction, we find that the density distributions of a Fermi gas in each spin state do not change significantly under the BCS transition, but the critical temperature is reduced significantly in comparison with the case without the fluctuation effect. The inclusion of the fluctuation correction effect for a large value of scattering length affects the expansion of a Fermi gas only in a minor way The expansion of a Fermi gas depends in a crucial way on whether the system is in the collisionless regime or in the hydrodynamic regime.

We discuss the expansion of an initially trapped dipolar condensate. When the nominal isotropic s-wave interaction strength becomes tunable through a Feshbach resonance, anisotropic dipolar effects are shown to be detectable under current experimental conditions [E. A. Donley et al., Nature London 412, 295 (2001)].

Squeezing of the coherent state by optical parametric amplifier is shown to efficiently produce single-photon states with reduced multiphoton probabilities compared with the weak coherent light. It can be a better source for a longer-distance quantum key distribution and also for other quantum optical experiments. The necessary condition for a secure quantum key distribution given by Brassard et al. is analyzed as functions of the coherent-state amplitude and squeeze parameter. Similarly, the rate of the gained secure bits G after error correction and privacy amplification given by Lütkenhaus is calculated. Compared with the weak coherent light, it is found that G is about ten times larger and its high level continues on about two times longer distance. By improvement of the detector efficiency it is shown that the distance extends further. Measurement of the intensity correlation function and the relation to photon antibunching are discussed for the experimental verification of the single-photon generation.

We describe the use of composite rotations to combat systematic errors in single-qubit quantum logic gates and discuss three families of composite rotations which can be used to correct off-resonance and pulse length errors. Although developed and described within the context of nuclear magnetic resonance quantum computing, these sequences should be applicable to any implementation of quantum computation.

We consider the problem of designing an optimal quantum detector with a fixed rate of inconclusive results that maximizes the probability of correct detection, when distinguishing between a collection of mixed quantum states. We show that the design of the optimal detector can be formulated as a semidefinite programming problem, and derive a set of necessary and sufficient conditions for an optimal measurement. We then develop a sufficient condition for the scaled inverse measurement to maximize the probability of correct detection for the case in which the rate of inconclusive results exceeds a certain threshold. Using this condition we derive the optimal measurement for linearly independent pure-state sets, and for mixed-state sets with a broad class of symmetries. Specifically, we consider geometrically uniform (GU) state sets and compound geometrically uniform (CGU) state sets with generators that satisfy a certain constraint. We then show that the optimal measurements corresponding to GU and CGU state sets with arbitrary generators are also GU and CGU, respectively, with generators that can be computed very efficiently in polynomial time within any desired accuracy by solving a reduced size semidefinite programming problem.

The time-dependent density-functional (TDDFT) equations may be written either for the Kohn-Sham orbitals in Hilbert space or for the single-electron density matrix in Liouville space. A collective-oscillator, quasiparticle, representation of the density response of many-electron systems which explicitly reveals the relevant electronic coherence sizes is developed using the Liouville-space representation of adiabatic TDDFT. Closed expressions for the nonlinear density-density response are derived, eliminating the need to solve nonlinear integral equations, as required in the Hilbert-space formulation of the response.

Convoy-electron emission produced by grazing-ion–surface scattering is studied in the framework of the distorted-wave theory. We develop a model, here named field distorted-wave (FDW) approximation, to describe the effect of the surface interaction on the electronic transition. In the model, the action of the surface field on the ejected electron is seen as an additional momentum transfer that depends on the projectile position. We apply the FDW approximation to analyze electron distributions for 100 keV protons impinging on LiF(100) and Al(111) surfaces, which are insulator and metal materials, respectively. In the case of metals, the dynamic screening of the projectile is included in the Jost function corresponding to the final state. As experimentally observed, energy spectra of forward-ejected electrons display a prominent structure associated with the convoy-electron emission. We find that the maximum of the convoy-electron distribution is decelerated for LiF and accelerated for Al, with respect to its position in ion-atom collisions, in quantitative agreement with the experimental data.