A method for coherent laser control of randomly oriented molecules at high temperatures (up to room temperature) is suggested, which rests on the technique proposed by us earlier of laser-assisted orientation-dependent selection (ODS) [Phys. Rev. A 77, 011401R (2008)]. It is shown that the ODS is of practical importance for the problem of field-free orientation of molecules. The efficacy of the method is justified by simulations of the photoinduced dynamics of BF molecules via direct numerical solution of the nonstationary Schrödinger equation.

Positronium decay into a muon-antimuon pair by virtue of the interaction with a superintense laser field of linear polarization is considered. The minimum laser intensity required amounts to a few ${10}^{22}\mathrm{W}∕{\mathrm{cm}}^2$ in the near-infrared frequency range. Within the framework of laser-dressed quantum electrodynamics, the total reaction rate is calculated and related to the cross section for field-free electron-positron annihilation into muons. The muons are created with ultrarelativistic energies and emitted under narrow angles along the laser propagation direction. The dynamical properties of the muons are interpreted in terms of a classical simple man’s model for the production process. We show that the most promising setup for an experimental investigation of the process in the near future is based on the combination of upcoming superintense laser sources with envisaged positron accumulation techniques: It employs two counterpropagating laser beams impinging on a positronium target, where the advantage of the coherent electron-positron collisions becomes evident.

We present extended experimental investigations and numerical studies on coherently driven population inversion in a three-state molecular quantum system by sequential double-Stark-chirped rapid adiabatic passage (SCRAP) (D-SCRAP) and three-state-SCRAP (T-SCRAP). D-SCRAP and T-SCRAP are alternative extensions of SCRAP. In D-SCRAP and T-SCRAP, a $\Lambda$-type quantum system is coherently driven by two laser pulses, the pump and Stokes pulses, which are slightly detuned from transition frequencies. A third strong laser pulse induces dynamic Stark shifts of the relevant transitions. If the timing of the three pulses is appropriately chosen, the quantum system is prepared to almost complete population inversion between the two lower states in the $\Lambda$-type level scheme. The transfer process is robust with regard to fluctuations of experimental parameters, provided some limitations are met. The paper presents convincing experimental data on D-SCRAP and T-SCRAP, driving efficient and selective population transfer to a highly excited vibrational level in nitrous oxide (NO) molecules. T-SCRAP yields transfer efficiencies of up to 95%. The efficiency of T-SCRAP is almost uneffected by the limited lifetime of the intermediate state in the $\Lambda$ system. The paper also presents data on the accurate experimental determination of Rabi frequencies and Stark shifts. This involves measurements of power broadening, Autler-Townes splittings, and Stark-shifted spectral lines in NO molecules. Moreover, we discuss the calibration of absolute transfer efficiences by comparison with stimulated emission pumping. The experimental data are confirmed by extended numerical simulations. The simulations also serve to intensively study the properties and dynamics of D-SCRAP and T-SCRAP.

We study Bose-Einstein condensates trapped in periodically shaken shallow optical lattices, and demonstrate the existence of subdiffractive solitons, analogous to those encountered in periodically blinking lattices [K. Staliunas, R. Herrero, and G. J. de Valcarcel, Phys. Rev. E 73, 065603(R) (2006)]. We also show that solitons in periodically shaken optical lattices radiate weakly into the near-to-resonance modes. For typical experimental conditions, however, the soliton lifetime turns out to be much longer than the typical lifetime of the condensate, therefore the subdiffractive solitons are expected to be observable in periodically shaken shallow optical lattices.

Simulations of harmonic generation in the single-atom limit usually describe the harmonic radiation as proportional to the squared magnitude of the Fourier transform (FT) of the expectation value of either the dipole moment or the dipole acceleration. However, no derivation of an explicit single-atom representation of the typical experimental measurement (i.e., the number of harmonic photons produced versus the frequency of the harmonic) has been given. By means of the first principles of quantum electrodynamics a formula for this “harmonic photon-number spectrum” is derived, which is proportional to the double FT of the time-autocorrelation function of the dipole velocity of the whole system. Within the long-wavelength approximation the time-correlation function can be recast as the FT of the squared magnitude of the expectation value of the dipole velocity of a single representative atom.

We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles and the polarization of the incident wave. The polarization-resolved angular (conoscopic) patterns emerging after the NLC cell illuminated by the convergent light beam are described in terms of the polarization singularities such as $C$ points (points of circular polarization) and $L$ lines (lines of linear polarization). For the homeotropically aligned cell, the Stokes polarimetry technique is used to measure the polarization resolved conoscopic patterns at different values of the ellipticity of the incident light, ${ϵ}_{\mathrm{ell}}^{\left(\mathrm{inc}\right)}$, impinging onto the cell. Using the exact analytical expressions for the transfer matrix we show that variations of the ellipticity, ${ϵ}_{\mathrm{ell}}^{\left(\mathrm{inc}\right)}$, induce transformations of the angular pattern exhibiting the effect of avoided $L$-line crossings and characterized by topological events such as creation and annihilation of the $C$ points. The predictions of the theory are found to be in good agreement with the experimental results.

We show that entanglement of two superposed coherent states produces sub-Planck structures in phase space. The origin of these structures depends entirely on entanglement, unlike those in Zurek [Nature (London) 412, 712 (2001)], where the effect of entanglement was not considered. The constituent states are sensitive enough to carry out the Heisenberg sensitive measurements. However, their usefulness is limited in providing high sensitivity in either the position $\left(x\right)$ direction or in the momentum $\left(p\right)$ direction of the phase-space. Interestingly, the entanglement causes the proposed states to be sensitive in both $x$ and $p$ directions. This state offers a better sensitivity compared to the single partite compass state in Zurek [Nature (London) 412, 712 (2001)] in carrying out precision measurements. It is also argued that such states are easy to create and are better suited for carrying out precision measurements.

The time-dependent Casimir-Polder force arising during the time evolution of an initially bare two-level atom, interacting with the radiation field and placed near a perfectly conducting wall, is considered. Initially the electromagnetic field is supposed to be in the vacuum state and the atom in its ground state. The analytical expression of the force as a function of time and atom-wall distance is evaluated from the time-dependent atom-field interaction energy. Physical features and limits of validity of the results are discussed in detail.

We construct a simple translationally invariant, nearest-neighbor Hamiltonian on a chain of ten-dimensional qudits that makes it possible to realize universal quantum computing without any external control during the computational process. We only require the ability to prepare an initial computational basis state that encodes both the quantum circuit and its input. The computational process is then carried out by the autonomous Hamiltonian time evolution. After a time polynomially long in the size of the quantum circuit has passed, the result of the computation is obtained with high probability by measuring a few qudits in the computational basis. This result also implies that there cannot exist efficient classical simulation methods for generic translationally invariant nearest-neighbor Hamiltonians on qudit chains, unless quantum computers can be efficiently simulated by classical computers (or, put in complexity theoretic terms, unless $\mathrm{BPP}=\mathrm{BQP}$).

Variational two-electron reduced-density-matrix (2RDM) theory is applied to computing energy spectra and properties of few-electron quantum dots. The model system is a two-dimensional electron gas with a central confinement potential. For each orbital angular momentum $J$, the energy and 2RDM are computed by the variational 2RDM method in which the energy is minimized as a functional of the 2RDM. In the minimization, which is performed by semidefinite programming, the 2RDM is constrained to represent a $N$-electron wave function with angular momentum $J$ by $N$- and $J$-representability conditions [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)]. Advantages of the variational 2RDM method include (i) lower bounds on the energies for all $J$ values, (ii) calculation of approximate 2RDMs in polynomial time without many-electron wave functions, (iii) exploitation of angular symmetry in the sparse block-diagonal structure of the 2RDM, (iv) accurate description of multireference correlation (entanglement) effects, and (v) direct calculation of one- and two-electron properties from the 2RDM. With the 2RDM we directly compute pair-correlation functions, radial charge densities, and average radial electron displacements in the quantum dot. Energies and properties are compared to those from solving the $N$-electron Schrödinger equation by large-scale, exact diagonalization. It is found that the accuracy of the variational 2RDM approach is sensitive to the total orbital angular momentum and the symmetry of the final wave function. For quantum dots of high symmetry, the variational algorithm isolates a highly accurate solution that recovers the correlation energy within a few percent.

High accuracy frequency metrology on the $4s{}^{2}S_{1∕2}–4p{}^{2}P_{1∕2}$ transition in calcium ions is performed using laser cooled and crystallized ions in a linear Paul trap. Calibration is performed with a frequency comb laser, resulting in a transition frequency of $f=755222766.2\left(1.7\right)\mathrm{MHz}$. The accuracy presents an improvement of more than one order of magnitude, and will facilitate a comparison with quasar data in a search for a possible change of the fine structure constant on a cosmological time scale.

The rate coefficient for thermionic emission of $\mathrm{S}\mathrm{F}_6{}^{-}$ is calculated from first principles, i.e., level densities of $\mathrm{S}{\mathrm{F}}_6$ and $\mathrm{S}\mathrm{F}_6{}^{-}$, the known electron attachment cross section, and the principle of detailed balance. The decay of $\mathrm{S}\mathrm{F}_6{}^{-}$ is calculated for different conditions in the $\mathrm{S}\mathrm{F}_6{}^{-}$ formation process. It is demonstrated that a power law as well as exponential decays may be obtained depending on the experimental conditions in a measurement of the $\mathrm{S}\mathrm{F}_6{}^{-}$ lifetime. The time dependence of the decay rate recently obtained at an electrostatic storage ring is accounted for by the obtained rate coefficient when the initial energy spread of $\mathrm{S}{\mathrm{F}}_6$ and the kinetic energy of the free electron prior to attachment are included.

We present two schemes for driving Raman transitions between the ground-state hyperfine manifolds of a single atom trapped within a high-finesse optical cavity. In both schemes, the Raman coupling is generated by standing-wave fields inside the cavity, thus circumventing the optical access limitations that free-space Raman schemes must face in a cavity system. These cavity-based Raman schemes can be used to coherently manipulate both the internal and motional degrees of freedom of the atom, and thus provide powerful tools for studying cavity quantum electrodynamics. We give a detailed theoretical analysis of each scheme, both for a three-level atom and for a multilevel cesium atom. In addition, we show how these Raman schemes can be used to cool the axial motion of the atom to the quantum ground state, and we perform computer simulations of the cooling process.

Magnon excitation in a spinor Bose-Einstein condensate by a driven magnetic field is shown to have a close analogy with the dynamical Casimir effect. A time-dependent external magnetic field amplifies quantum fluctuations in the magnetic ground state of the condensate, leading to magnetization of the system. The magnetization occurs in a direction perpendicular to the magnetic field breaking the rotation symmetry. This phenomenon is numerically demonstrated and the excited quantum field is shown to be squeezed.

We demonstrate the generation of multiphoton quantum states of light by cavity-enhanced parametric down-conversion in the high-repetition-rate pulsed regime. An external enhancement cavity resonant with the spectral comb of modes of a mode-locked pump laser provides a coherent buildup of the pump intensity and greatly enhances the parametric gain without sacrificing its high repetition rate and comb structure. We probe the parametric gain enhancement by the conditional generation and tomographic analysis of two-photon Fock states. Besides its potential impact for efficiently generating highly nonclassical or entangled multiphoton states in many existing experimental setups, this scheme opens exciting perspectives toward the combination of quantum and comb technologies for enhanced measurements and advanced quantum computation protocols.

The polarization process when polarizers act on an optical field is studied. We give examples for two kinds of polarizers. The first kind presents an anisotropic absorption—as in a Polaroid film—and the second one is based on total reflection at the interface with a birefringent medium. Using the Stokes vector representation, we determine explicitly the trajectories of the wave light polarization during the polarization process. We find that such trajectories are not always geodesics of the Poincaré sphere as is usually thought. Using the analogy between light polarization and special relativity, we find that the action of successive polarizers on the light wave polarization is equivalent to the action of a single resulting polarizer followed by a rotation achieved, for example, by a device with optical activity. We find a composition law for polarizers similar to the composition law for noncollinear velocities in special relativity. We define an angle equivalent to the relativistic Wigner angle which can be used to quantify the quality of two composed polarizers.

We analyze quantum correlations in four-wave mixing in three-level $\Lambda$ and V atomic systems by using dressed atomic states and squeeze-transformed cavity modes. Two dissipation channels are identified, through which the dressed atoms simultaneously absorb in the excitations from the pair of squeeze-transformed modes. It is in the presence of two channels that the entanglement is greatly enhanced and the best achievable state approaches the original Einstein-Podolsky-Rosen entangled state. This scheme is applicable in the optical regime where atomic spontaneous emission has to be taken into account, unlike the two-step atomic reservoir engineering scheme, which is limited to the microwave regime.

We present a theoretical roadmap for three-dimensional optical waveguide networks in holographically defined, diamondlike photonic band gap (PBG) materials. A fully 3D waveguide network is demonstrated through broadband $(100–200\mathrm{nm})$, single-mode waveguiding in air, coupled with sharp bends in three dimensions with minimal backscattering. Optimal waveguides in the in-plane $x$ and $y$ directions are shown to exhibit nearly $250\mathrm{nm}$ of single-mode bandwidth for light of wavelengths near $1.5\mu \mathrm{m}$. Vertical waveguide channels are formed by introducing air defects in a zigzag pattern. Realization of these circuit designs may be achieved through the combination of direct laser writing of defects within the holographically defined photoresist and the subsequent replication of the microchip template with a high refractive index semiconductor such as silicon.

Taking into account the characteristics of a free scalar field in elliptic coordinates, a new dynamical variable is found for the free electromagnetic field. The conservation law associated to this variable cannot be obtained by direct application of standard Noether theorem since the symmetry generator is of second order. Consequences on the expected mechanical behavior of an atomic system interacting with electromagnetic waves exhibiting such a symmetry are also discussed.

Highly accurate computations of the van der Waals dispersion coefficients of hydrogen are presented. Using the variationally stable method of Gao and Starace [Phys. Rev. Lett. 61, 404 (1988); Phys. Rev. A 39, 4550 (1989)], we report results for the $C_6$ and $C_9$ coefficients to 28 and 34 significant digits, respectively. Comparisons are given to results of prior work. The present values can be used as a benchmark for other approaches.