We present a theoretical study of one-photon single ionization of ${\text{H}}_2^{+}$, ${\text{H}}_2$, and ${\text{Li}}_2^{+}$ with circularly polarized light of a few hundred eV (a few tens of eV for ${\text{Li}}_2^{+}$). At these photon energies, two-center interference effects due to confinement and double-slit diffraction are expected. The results show that, in general, the calculated angular distributions for circularly polarized light are very similar to those obtained by incoherently averaging the angular distributions for parallel and perpendicular linearly polarized light. Thus, at the lower photon energies, the multiple lobes observed in the angular distributions for circularly polarized light (which are absent for linearly polarized light) have little to do with confinement and/or double-slit diffraction. At the higher photon energies, such effects do exist, but they are partly hidden and are much more difficult to analyze than for linearly polarized light. The simple diffraction interpretation is even less applicable for ${\text{H}}_2$ and ${\text{Li}}_2^{+}$ because confinement and double-slit diffraction appear at electron energies too low to ignore electron correlation and the details of the molecular potential.

We report on a technique to split an atomic beam coherently with an easily adjustable splitting angle. In our experiment metastable helium atoms in the $|\left\{1s2s\right\}{{}^{3}S}_{1}M=1⟩$ state diffract from a polarization gradient light field formed by counterpropagating ${\sigma }^{+}$ and ${\sigma }^{-}$ polarized laser beams in the presence of a homogeneous magnetic field. In the near-adiabatic regime, energy conservation allows the resonant exchange between magnetic energy and kinetic energy. As a consequence, symmetric diffraction of $|M=0⟩$ or $|M=-1⟩$ atoms in a single order is achieved, where the order can be chosen freely by tuning the magnetic field. We present experimental results up to sixth-order diffraction ($24\hslash k$ momentum splitting, i.e., 2.21 m/s in transverse velocity) and present a simple theoretical model that stresses the similarity with conventional Bragg scattering. The resulting device constitutes a flexible, adjustable, large-angle, three-way coherent atomic beam splitter with many potential applications in atom optics and atom interferometry.

We propose an experimentally accessible procedure for conditional preparation of highly nonclassical states of collective spin of an atomic ensemble. The quantum state engineering is based on a combination of quantum nondemolition interaction between atoms and light previously prepared in a non-Gaussian state using photon subtraction from squeezed vacuum beam, homodyne detection on the output light beam, and a coherent displacement of atomic state. The procedure is capable of nondeterministic preparation of a wide class of superpositions of atomic Dicke states. We present several techniques to optimize the performance of the protocol and maximize the trade off between fidelity of prepared state and success probability of the scheme.

Recent studies of singularities in scalar wave fields in Young’s classic experiment are extended to electromagnetic fields diffracted by an $N$-pinhole interferometer. Linearly polarized fields whose direction of polarization may be different at each pinhole are examined. It is shown that for two pinholes, only surfaces of linear polarization are created. For $N$ larger than two, a rich structure of polarization singularities is found even when the location of the pinholes is arbitrary. In addition, there can be regions where the spectral density of the field is zero.

In this paper we derive analytical relations between probabilities of the excited state transfers and entanglements calculated by both the Wootters and positive partial transpose criteria for the arbitrary spin system with single excited spin in the external magnetic field and Hamiltonian commuting with $I_z$. We apply these relations to study the arbitrary state transfers and entanglements in the simple systems of nuclear spins having two- and three-dimensional geometrical configurations with $XXZ$ Hamiltonian. It is shown that high-probability state transfers (HPSTs) are possible among all four nodes placed in the corners of the rectangle with the proper ratio of sides as well as among all eight nodes placed in the corners of the parallelepiped with the proper ratio of sides. Entanglements responsible for these HPSTs have been identified.

We propose a protocol of the long-distance atomic-state teleportation via cavity decay, which allows for high-fidelity teleportation even with currently available optical cavities. The protocol is based on the scheme proposed by Bose et al. [Phys. Rev. Lett. 83, 5158 (1999)] but with one important modification: it employs non-maximally-entangled states instead of maximally entangled states.

Optimization of the mean efficiency for unambiguous (or error-free) discrimination among $N$ given linearly independent nonorthogonal states should be realized in a way to keep the probabilistic quantum-mechanical interpretation. This imposes a condition on a certain matrix to be positive semidefinite. We reformulated this condition in such a way that the conditioned optimization problem for the mean efficiency was reduced to finding an unconditioned maximum of a function defined on a unit $N$ sphere for equiprobable states and on an $N$ ellipsoid if the states are given with different probabilities. We established that for equiprobable states a point on the sphere with equal values of Cartesian coordinates, which we call symmetric point, plays a special role. Sufficient conditions for a vector set are formulated for which the mean efficiency for equiprobable states takes its maximal value at the symmetric point. This set, in particular, includes previously studied symmetric states. A subset of symmetric states, for which the optimal measurement corresponds to a positive-operator-valued measure (POVM) requiring a one-dimensional ancilla space is constructed. We presented our constructions of a POVM suitable for the ancilla space dimension varying from 1 to $N$ and the Neumark extension differing from the existing schemes by the property that it is straightforwardly applicable to the case when it is desirable to present the whole space $\text{system}+\text{ancilla}$ as the tensor product of a two-dimensional ancilla space and the $N$-dimensional system space.

Exchange interaction strongly influences the long-range behavior of localized electron orbitals and quantum tunneling amplitudes. It produces a power-law decay instead of the usual exponential decrease at large distances. For inner orbitals inside molecules decay is $r^{-2}$, for macroscopic systems $\text{cos}\left(k_{F}r\right)r^{-\nu }$, where $k_F$ is the Fermi momentum and $\nu =3$ for one-dimensional, $\nu =3.5$ for two-dimensional, and $\nu =4$ for three-dimensional crystals. Correlation corrections do not change these conclusions. Slow decay increases the exchange interaction between localized spins and the underbarrier tunneling amplitude. The underbarrier transmission coefficients in solids (e.g., for point contacts) become temperature dependent.

We study the phase separation of a Bose-Einstein condensate system with the conversion of one-species bosonic atoms into molecules via Feshbach resonance. Adopting the Thomas-Fermi approximation, we plot the phase diagrams of the system in two different parameter spaces for different atom-molecule interactions. In the presence of an isotropic trap, the density profiles in spatial space with fixed total number of atoms are also plotted. The clear phase separation in spatial space enables one to determine the location of atoms in the trap, which may be used as a possible experimental probe method.

We study the dynamics of a nonintegrable system comprising interacting cold bosons trapped in an optical lattice in one dimension by means of exact time-dependent numerical density-matrix renormalization group techniques. Particles are confined by a parabolic potential, and dipole oscillations are induced by displacing the trap center of a few lattice sites. Depending on the system parameters this motion can vary from undamped to overdamped. We study the dipole oscillations as a function of the lattice displacement, the particle density, and the strength of interparticle interactions. These results explain the recent experiment [C. D. Fertig et al., Phys. Rev. Lett. 94, 120403 (2005)].

Quasimodes of an open finite-size two-dimensional (2D) random system are computed and systematically characterized in terms of their spatial extension $\eta$, complexity factor $q^2$, and phase distribution for a collection of random systems ranging from weakly scattering to localized systems. A rapid change is seen in $\eta$ and $q^2$ at the crossover from localized to diffusive which corresponds to the emergence of 2D extended multipeaked quasimodes analogous to the necklace states recently observed in one dimension. These 2D quasimodes are interpreted in terms of coupled localized states.

Couplings between quantum systems are frequently less robust and harder to implement than controls on individual systems; thus, constructing quantum gates with minimal interactions is an important problem in quantum computation. In this paper we study the optimal synthesis of two-qubit quantum gates for the tunable coupling scheme of coupled superconducting qubits and compute the minimal interaction time of generating any two-qubit quantum gate.

We carry out relativistic many-body calculations of the Stark-induced absorption coefficient on the 254-nm $6s6p{{}^{3}P}_1\left(F=1/2\right)–6s^2{{}^{1}S}_0$ line of ${}^{199}\text{H}\text{g}$ atom, the effect considered before by and Lamoreaux and Fortson [Phys. Rev. A 46, 7053 (1992)] using a simple central field estimate. The Stark-induced admixing of states of opposite parity opens additional $M1$ and $E2$ transition channels. We find that the resulting $M1\text{−}E1$ absorption dominates over $E2\text{−}E1$ absorption. The value of the $E2\text{−}E1$ absorption coefficient depends strongly on the details of treatment of the correlation problem. As a result, our numerical values differ substantially from those of the earlier central field calculation. Reliable calculation of this effect can enable a useful experimental check on the optical technique being used to search for a permanent electric-dipole moment of the ${}^{199}\text{H}\text{g}$ atom.

We perform convergent close-coupling calculations of double photoionization (DPI) of the $K$-shell of alkaline-earth metal atoms (Be, Mg, and Ca) from the threshold to the nonrelativistic limit of infinite photon energy. Theoretical double-to-single photoionization cross-section ratios for Mg and Ca are compared with experimental values derived from high-resolution x-ray spectra following the radiative decay of the $K$-shell double vacancy. We investigate the role of many-electron correlations in the ground and doubly-ionized final states played in the DPI process. Universal scaling of DPI cross section with an effective nuclear charge is examined in neutral atoms in comparison with corresponding heliumlike ions.

Optical trapping of radioactive atoms has a great potential in precision measurements for testing fundamental physics such as electric-dipole moment, atomic parity nonconservation, and parity-violating $\beta$-decay correlation coefficients. One challenge that remains is to polarize the atoms to a high degree, and to measure the polarization of the sample and its evolution over time. In this paper we report on the polarization study of Rb atoms in a yttrium-aluminum-garnet (YAG)-laser optical dipole trap using both Faraday rotation polarimetry and resolved Zeeman spectroscopy techniques. We have prepared a cold cloud of polarized atoms and observed that its spin relaxation due to light scattering is suppressed in the YAG dipole trap. The spin polarization is further purified and maintained when the two-body collision loss rate between atoms in mixed spin states is greater than the one-body trap loss. These advancements are an important step toward a new generation of precision measurement with polarized trapped atoms.

We show how wave functions with the same energy and probability distribution but different momenta have very different dissociation probabilities when two molecular potentials are strongly coupled by an intense laser field. Our measurements of dynamics in a molecular family, in conjunction with molecular structure and wave-packet calculations, highlight the role of the wave-packet momentum, or spatially varying phase, in the dynamics leading to dissociation. Phase-dependent dynamics are central to coherent control of laser driven chemistry.

Original quantum repeater protocols based on the single-photon interference suffer from the phase noise of the channel, which makes the long-distance quantum communication infeasible. Fortunately, two-photon interferencelike quantum repeaters can be immune to the phase noise of the channel. However, this type of quantum repeaters may still suffer from polarization disturbance of the channel. Here we propose a quantum repeaters protocol, which is free of the polarization disturbance of the channel based on the invariance of the antisymmetric Bell state $|{\psi }^{-}⟩=\left(|H⟩|V⟩-|V⟩|H⟩\right)/\sqrt{2}$ under collective noise. Our protocol is also immune to the phase noise with the Sagnac interferometer configuration. Through single-atom cavity-QED technology and linear optics, this scheme can be implemented easily.

We investigate the laser-induced ionization and Coulomb explosion of CO with a time-of-flight mass spectrometer. A field-assisted bond-stretching model is proposed to interpret the different mass spectra observed in intense laser fields with different pulse durations.