We propose a protocol to generate a stream of mobile qubits in a graph state through a single stationary parent qubit and discuss two types of its physical implementation, namely, the generation of photonic graph states through an atomlike qubit and the generation of flying atoms through a cavity-mode photonic qubit. The generated graph states fall into an important class that can hugely reduce the resource requirement of fault-tolerant linear optics quantum computation, which was previously known to be far from realistic. In regard to the flying atoms, we also propose a heralded generation scheme, which allows for high-fidelity graph states even under the photon loss.

We exploit a microscopically derived master equation for the study of stimulated Raman adiabatic passage in the presence of spontaneous decay from the intermediate state toward the initial and final states and compare our results with the predictions obtained from a phenomenological model used previously [P. A. Ivanov, N. V. Vitanov, and K. Bergmann, Phys. Rev. A 72, 053412 (2005)]. It is shown that our approach predicts a much higher efficiency for counterintuitively ordered pulses, while no significant difference between the two approaches is found for intuitively ordered pulses. These features are readily explained in the dressed-state picture.

Very accurate variational nonrelativistic calculations are performed for the five lowest Rydberg ${}^{2}D$ states ($1s^2{\mathit{nd}}^1$, $n=3,\dots ,7$) of the lithium atom (${}^7\mathrm{Li}$). The finite-nuclear-mass approach is employed and the wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian function. Four thousand Gaussians are used for each state. The calculated relative energies of the states determined with respect to the ${}^{2}S$ $1s^{2}2s^1$ ground state are systematically lower than the experimental values by about 2.5 cm${}^{-1}$. As this value is about the same as the difference between the experimental relative energy between ${}^7\mathrm{Li}$${}^{+}$ and ${}^7\mathrm{Li}$ in their ground-state energy and the corresponding calculated nonrelativistic relative energy, we attribute it to the relativistic effects not included in the present calculations.

In the strong interaction limit, attractive fermions with $N$-component hyperfine states in a one-dimensional waveguide form unbreakable bound cluster states. We demonstrate that the ground state of strongly attractive SU($N$) Fermi gases can be effectively described by a super Tonks-Girardeau gaslike state composed of bosonic cluster states with strongly attractive cluster-cluster interaction for even $N$ and a Fermi duality of a super Tonks-Girardeau gaslike state composed of fermionic cluster states with weakly interacting cluster-cluster $p$-wave interaction for odd $N$.

We study the formation of Faraday waves in an elongated Bose-Einstein condensate in the presence of a one-dimensional optical lattice. The waves are parametrically excited by modulating the radial confinement of the condensate close to a transverse breathing mode of the system. For very shallow optical lattices, phonons with a well-defined wave vector propagate along the condensate, as in the absence of the lattice, and we observe the formation of a Faraday pattern. We find that by increasing the potential depth the local sound velocity decreases, and when it equals the condensate local phase velocity, the condensate develops an incoherent superposition of several modes and the parametric excitation of Faraday waves is suppressed.

In this paper we investigate the photonic tunneling effect between two coupled one-atom laser cavities. The physical system consists of two coupled photonic crystal microcavities and each cavity contains a coherently pumped two-level atom. The dynamics of the system can be described by the master equation in terms of the reduced density operator. It is shown that the photonic tunneling behavior depends on certain physical conditions of the system. In the absence of the pumping field and without dissipations, the coherent photon number imbalance between two cavities exhibits the alternating-current Josephson effect. However, when the pumping effect and losses of the system are taken into account, the mean photon number imbalance displays a damped oscillation. In addition, the influence of tunneling amplitude and photonic band-gap structure on the oscillations is also studied. The research gives a further insight into the correlated dynamics of two coupled one-atom laser systems and provides an idea for constructing novel photon tunnel devises.

We show that the ability to create entanglement is necessary for execution of bipartite quantum gates even when they are applied to unentangled states and create no entanglement. Starting with a simple example we demonstrate that to execute such a gate bilocally the local operations and classical communications (LOCC) should be supplemented by shared entanglement. Our results point to the changes in quantum discord, which is a measure of quantumness of correlations even in the absence of entanglement, as the indicator of failure of a LOCC implementation of the gates.

A harmonically trapped, ultracold, one-dimensional (1D) spin-1 Bose gas with strongly repulsive or attractive 1D even-wave interactions induced by a three-dimensional (3D) Feshbach resonance is studied. The exact ground state, a hybrid of Tonks-Girardeau (TG) and ideal Fermi gases, is constructed in the TG limit of infinite even-wave repulsion by a spinor Fermi-Bose mapping to a spinless ideal Fermi gas. It is then shown that in the limit of infinite even-wave attraction this same state remains an exact many-body eigenstate, now highly excited relative to the collapsed generalized McGuire-cluster ground state, showing that the hybrid TG state is completely stable against collapse to this cluster ground state under a sudden switch from infinite repulsion to infinite attraction. It is shown to be the TG limit of a hybrid super-Tonks-Girardeau (STG) state, which is metastable under a sudden switch from finite but very strong repulsion to finite but very strong attraction. It should be possible to create it experimentally by a sudden switch from strongly repulsive to strongly attractive interaction, as in the recent Innsbruck experiment on a spin-polarized bosonic STG gas. In the case of strong attraction, there should also exist another STG state of much lower energy, consisting of strongly bound dimers, a bosonic analog of a recently predicted STG state which is an ultracold gas of strongly bound bosonic dimers of fermionic atoms, but it is shown that this STG state cannot be created by such a switch from strong repulsion to strong attraction.

We have developed an all-particle Fock-space relativistic coupled-cluster method for two-valence atomic systems. We then describe a scheme to employ the coupled-cluster wave function to calculate atomic properties. Based on these developments we calculate the excitation energies, magnetic hyperfine structure constants, and electric dipole matrix elements of Sr, Ba, and Yb. Furthermore, we calculate the electric quadrupole hyperfine structure constants and the electric dipole matrix elements of ${\mathrm{Sr}}^{+}$, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Yb}}^{+}$. For these we use the one-valence coupled-cluster wave functions obtained as an intermediate in the two-valence calculations. We also calculate the magnetic dipole hyperfine structure constants of ${\mathrm{Yb}}^{+}$.

We have performed an accurate frequency calibration of the $4s^2\hspace{0.5em}{}^1{S}_0\to 4s4p\hspace{0.5em}{}^1{P}_1$ principal resonance line of the neutral calcium atom at 423 nm. Doppler-free cw excitation on a Ca atomic beam was performed by utilizing a Sagnac geometry in the alignment of the excitation beams. From frequency calibrations against a frequency comb, stabilized to a global positioning system (GPS) disciplined Rb standard, the transition frequency is determined at 709 078 373.01(35) MHz for the main ${}^{40}\mathrm{Ca}$ isotope. Slightly lower accuracies are obtained for the transition frequencies of the less abundant isotopes. The achieved fractional uncertainty of $5\times {10}^{-10}$ exceeds the requirements for including this transition in investigations that aim to probe a possible variation in the fine-structure constant $\alpha$ on cosmological time scales.

A systematic study of Ca${}^{+}$ atomic properties is carried out using a high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Reduced matrix elements, oscillator strengths, transition rates, and lifetimes are determined for the levels up to $n=7$. Recommended values and estimates of their uncertainties are provided for a large number of electric-dipole transitions. Electric-dipole scalar polarizabilities for the $5s$, $6s$, $7s$, $8s$, $4p_j$, $5p_j$, $3d_j$, and $4d_j$ states and tensor polarizabilities for the $4p_{3/2}$, $5p_{3/2}$, $3d_j$, and $4d_j$ states in Ca${}^{+}$ are calculated. Methods are developed to accurately treat the contributions from highly excited states, resulting in significant (factor of 3) improvement in the accuracy of the $3d_{5/2}$ static polarizability value, $31.8(3)a_0^3$, in comparison with the previous calculation [Arora et al., Phys. Rev. A 76, 064501 (2007).]. The blackbody radiation shift of the $4s–3d_{5/2}$ clock transition in Ca${}^{+}$ is calculated to be $0.381(4)$ Hz at room temperature, $T=300$ K. Electric-quadrupole $4s–\mathit{nd}$ and electric-octupole $4s–\mathit{nf}$ matrix elements are calculated to obtain the ground-state multipole $E2$ and $E3$ static polarizabilities. Excitation energies of the $\mathit{ns}$, $\mathit{np}$, $\mathit{nd}$, $\mathit{nf}$, and $\mathit{ng}$ states with $n⩽$ 7 in are evaluated and compared with experiment. Recommended values are provided for the $7p_{1/2}$, $7p_{3/2}$, $8p_{1/2}$, and $8p_{3/2}$ removal energies for which experimental measurements are not available. The hyperfine constants $A$ are determined for the low-lying levels up to $n=7$. The quadratic Stark effect on hyperfine structure levels of ${}^{43}\mathrm{Ca}$${}^{+}$ ground state is investigated. These calculations provide recommended values critically evaluated for their accuracy for a number of Ca${}^{+}$ atomic properties for use in planning and analysis of various experiments as well as theoretical modeling.

A QED approach to the calculation of the spectra of the lithium isoelectronic sequence is implemented. A modified Furry representation based on the Kohn-Sham potential is used to evaluate all one- and two-photon diagrams with the exception of the two-loop Lamb shift. Three-photon diagrams are estimated with Hamiltonian methods. After incorporating recent calculations of the two-loop Lamb shift and recoil corrections, a comprehensive tabulation of the $2s$, $2p_{1/2}$, and $2p_{3/2}$ energy levels as well as the $2s–2p_{1/2}$ and $2s–2p_{3/2}$ transition energies for $Z=10-100$ is presented.

Saturated absorption spectra of the ${\nu }_1$ fundamental band of CH${}_3$I are recorded with a cavity-enhanced cell and a tunable difference frequency generation source having an 86-cm${}^{-1}$ range. The recorded spectral lines are 250 kHz wide, and most of them are resolved into the individual hyperfine components. The Coriolis interaction between the $v_1=1$ and $(v_2,v_6^l)=(1,2^2)$ states locally perturbing the hyperfine structures is analyzed to yield the Coriolis and hyperfine coupling constants with uncertainties similar to those in typical microwave spectroscopy. The spectrometer has demonstrated the potential for precisely determining the energy structure in the vibrational excited states.

Dielectronic recombination (DR) of Na-like Fe${}^{15+}$ forming Mg-like Fe${}^{14+}$ via excitation of a $2l$ core electron has been investigated. We find that configuration interaction (CI) between DR resonances with different captured electron principal quantum numbers $n$ can lead to a significant reduction in resonance strengths for $n⩾5$. Previous theoretical work for this system has not considered this form of CI. Including it accounts for most of the discrepancy between previous theoretical and experimental results.

Atom counting theory can be used to study the role of thermal noise in quantum phase transitions and to monitor the dynamics of a quantum system. We illustrate this for a strongly correlated fermionic system, which is equivalent to an anisotropic quantum $\mathit{XY}$ chain in a transverse field and can be realized with cold fermionic atoms in an optical lattice. We analyze the counting statistics across the phase diagram in the presence of thermal fluctuations and during its thermalization when the system is coupled to a heat bath. At zero temperature, the quantum phase transition is reflected in the cumulants of the counting distribution. We find that the signatures of the crossover remain visible at low temperature and are obscured with increasing thermal fluctuations. We find that the same quantities may be used to scan the dynamics during the thermalization of the system.

We provide a general quantum theory to describe the coupling of light with the motion of a dielectric object inside a high-finesse optical cavity. In particular, we derive the total Hamiltonian of the system as well as a master equation describing the state of the center-of-mass mode of the dielectric and the cavity-field mode. In addition, a quantum theory of elasticity is used to study the coupling of the center-of-mass motion with internal vibrational excitations of the dielectric. This general theory is applied to the recent proposal of using an optically levitating nanodielectric as a cavity optomechanical system [see Romero-Isart et al., New J. Phys. 12, 033015 (2010); Chang et al., Proc. Natl. Acad. Sci. USA 107, 1005 (2010)]. On this basis, we also design a light-mechanics interface to prepare non-Gaussian states of the mechanical motion, such as quantum superpositions of Fock states. Finally, we introduce a direct mechanical tomography scheme to probe these genuine quantum states by time-of- flight experiments.

The conventional orientation-averaging procedure developed in the framework of the superposition $T$-matrix approach is generalized to include the case of illumination by a Gaussian beam (GB). The resulting computer code is parallelized and used to perform extensive numerically exact calculations of electromagnetic scattering by volumes of discrete random medium consisting of monodisperse spherical particles. The size parameters of the scattering volumes are 40, 50, and 60, while their packing density is fixed at $5\%$. We demonstrate that all scattering patterns observed in the far-field zone of a random multisphere target and their evolution with decreasing width of the incident GB can be interpreted in terms of idealized theoretical concepts such as forward-scattering interference, coherent backscattering (CB), and diffuse multiple scattering. It is shown that the increasing violation of electromagnetic reciprocity with decreasing GB width suppresses and eventually eradicates all observable manifestations of CB. This result supplements the previous demonstration of the effects of broken reciprocity in the case of magneto-optically active particles subjected to an external magnetic field.

We experimentally measured the supercontinuum generation using 3-J, 30-fs laser pulses and measured white-light generation at the level of 1 J. Such high energy is allowed by a strong contribution to the continuum by the photon bath, as compared to the self-guided filaments. This contribution due to the recently observed congestion of the filament number density in the beam profile at very high intensity also results in a wider broadening for positively chirped pulses rather than for negatively chirped ones, similar to broadening in hollow-core fibers.

We show that a periodic two-dimensional (2D) photonic lattice with Kerr nonlinearity exhibits a Berezinskii-Kosterlitz-Thouless (BKT) crossover associated with a vortex-unbinding transition. We find that averaging over random initial conditions is equivalent to Boltzmann thermal averaging with the discrete nonlinear Schr$\stackrel{\mathrm{··}}{\mathrm{o}}$dinger Hamiltonian. By controlling the initial randomness we can continuously vary the effective temperature. Since this Hamiltonian is in the 2D $\mathit{XY}$ universality class, a BKT transition ensues. We verify this prediction using experimentally accessible observables and find good agreement between theory and simulations. This opens the possibility of experimental access to interesting phase transitions known in condensed matter using nonlinear optics.