Hydrogen in chemical atoms;

Accompanied by "Supplement [no.1]- " (V.) Published: Pittsburgh, Markowitz and Haas, 1951-

Chemical kinetics of reactions of the sulphur oxides, S-atoms, SH and H₂S; dissociation, photolysis and reactions with H, O, O₂, O₃ and the nitrogen oxides.

"Based on the files of the Chemical Kinetics Information Center and an examination of Chemical abstracts 1962-1970."

Entanglement of two atoms

We discuss the problem of creation of entangled states in a system of two two-level atoms which are separated by an arbitrary distance r(12) and interact with each other via the dipole-dipole interaction and both are driven by a laser field. The entangled antisymmetric state of the system is included throughout, even for small inter-atomic separations. Different mechanisms leading to effective transfer of population to the antisymmetric state are identified. The steady-state values of concurrence which is a measure of entanglement are calculated showing that perfect entanglement can be reached in case of two non-identical atoms.

Entangling two atoms via spontaneous emission

We discuss the creation of entanglement between two two-level atoms in the dissipative process of spontaneous emission. It is shown that spontaneous emission can lead to a transient entanglement between the atoms even if the atoms were prepared initially in an unentangled state. The amount of entanglement created in the system is quantified by using two different measures: concurrence and negativity. We find analytical formulae for the evolution of concurrence and negativity in the system. We also find the analytical relation between the two measures of entanglement. The system consists of two two-level atoms which are separated by an arbitrary distance r(12) and interact with each other via the dipole-dipole interaction, and the antisymmetric state of the system is included throughout, even for small interatomic separations, in contrast to the small-sample model. It is shown that for sufficiently large values of the dipole-dipole interaction initially the entanglement exhibits oscillatory behaviour with considerable entanglement in the peaks. For longer times the amount of entanglement is directly related to the population of the slowly decaying antisymmetric state.

Dynamical creation of entanglement by homodyne-mediated feedback

For two two-level atoms coupled to a single Bosonic mode that is driven and heavily damped, the steady state can be entangled by resonantly driving the system [S. Schneider and G. J. Milburn, Phys. Rev. A 65, 042107 (2002)]. We present a scheme to significantly increase the steady-state entanglement by using homodyne-mediated feedback, in which the Bosonic mode is that of an electromagnetic cavity, the output of which is measured and the resulting homodyne photocurrent is used to modulate the field driving the qubits. Such feedback can increase the nonlinear response to both the decoherence process of the two-qubit system and the coherent evolution of individual qubits. We present the properties of the entangled states using the SO(3) Q function.

New insights into the interaction of hydrogen atoms with boron-substituted carbon

Boron substitution in carbon materials has been comprehensively investigated using the density functional theory method. It was found that there is a correlation between the stability of the graphene sheet, the distribution of T electrons, the electrostatic potential, and the capability for hydrogen-atom adsorption. Boron substitution destabilizes the graphene structure, increases the density of the electron wave around the substitutional boron atoms, and lowers the electrostatic potential, thus improving the hydrogen adsorption energy on carbon. However, this improvement is only ca. 10-20% instead of a factor of 4 or 5. Our calculations also show that two substitutional boron atoms provide consistent and reliable results, but one substitutional boron results in contradictory conclusions. This is a warning to other computational chemists who work on boron substitution that the conclusion from one substitutional boron might not be reliable.

Bifurcations in the non-dissipative dynamics of ultra cold atoms

We present the first experimental observation of several bifurcations in a controllable non-linear Hamiltonian system. Dynamics of cold atoms are used to test predictions of non-linear, non-dissipative Hamiltonian dynamics.

Visualising and controlling the flow in biomolecular systems at and between multiple scales:from atoms to hydrodynamics at different locations in time and space

A novel framework for modelling biomolecular systems at multiple scales in space and time simultaneously is described. The atomistic molecular dynamics representation is smoothly connected with a statistical continuum hydrodynamics description. The system behaves correctly at the limits of pure molecular dynamics (hydrodynamics) and at the intermediate regimes when the atoms move partly as atomistic particles, and at the same time follow the hydrodynamic flows. The corresponding contributions are controlled by a parameter, which is defined as an arbitrary function of space and time, thus, allowing an effective separation of the atomistic 'core' and continuum 'environment'. To fill the scale gap between the atomistic and the continuum representations our special purpose computer for molecular dynamics, MDGRAPE-4, as well as GPU-based computing were used for developing the framework. These hardware developments also include interactive molecular dynamics simulations that allow intervention of the modelling through force-feedback devices.

Universal duality in a Luttinger liquid coupled to a generic environment

We study a Luttinger liquid (LL) coupled to a generic environment consisting of bosonic modes with arbitrary density-density and current-current interactions. The LL can be either in the conducting phase and perturbed by a weak scatterer or in the insulating phase and perturbed by a weak link. The environment modes can also be scattered by the imperfection in the system with arbitrary transmission and reflection amplitudes. We present a general method of calculating correlation functions under the presence of the environment and prove the duality of exponents describing the scaling of the weak scatterer and of the weak link. This duality holds true for a broad class of models and is sensitive to neither interaction nor environmental modes details, thus it shows up as the universal property. It ensures that the environment cannot generate new stable fixed points of the renormalization group flow. Thus, the LL always flows toward either conducting or insulating phase. Phases are separated by a sharp boundary which is shifted by the influence of the environment. Our results are relevant, for example, for low-energy transport in (i) an interacting quantum wire or a carbon nanotube where the electrons are coupled to the acoustic phonons scattered by the lattice defect; (ii) a mixture of interacting fermionic and bosonic cold atoms where the bosonic modes are scattered due to an abrupt local change of the interaction; (iii) mesoscopic electric circuits.

Nonlinear optical effects manifested by electromagnetic induced transparency in cold atoms

This dissertation reports experimental studies of nonlinear optical effects manifested by electromagnetically induced transparency (EIT) in cold Rb atoms. The cold Rb atoms are confined in a magneto-optic trap (MOT) obtained with the standard laser cooling and trapping technique. Because of the near zero Doppler shift and a high phase density, the cold Rb sample is well suited for studies of atomic coherence and interference and related applications, and the experiments can be compared quantitatively with theoretical calculations. It is shown that with EIT induced in the multi-level Rb system by laser fields, the linear absorption is suppressed and the nonlinear susceptibility is enhanced, which enables studies of nonlinear optics in the cold atoms with slow photons and at low light intensities. Three independent experiments are described and the experimental results are presented. First, an experimental method that can produce simultaneously co-propagating slow and fast light pulses is discussed and the experimental demonstration is reported. Second, it is shown that in a three-level Rb system coupled by multi-color laser fields, the multi-channel two-photon Raman transitions can be manipulated by the relative phase and frequency of a control laser field. Third, a scheme for all-optical switching near single photon levels is developed. The scheme is based on the phase-dependent multi-photon interference in a coherently coupled four-level system. The phase dependent multi-photon interference is observed and switching of a single light pulse by a control pulse containing ∼20 photons is demonstrated. These experimental studies reveal new phenomena manifested by quantum coherence and interference in cold atoms, contribute to the advancement of fundamental quantum optics and nonlinear optics at ultra-low light intensities, and may lead to the development of new techniques to control quantum states of atoms and photons, which will be useful for applications in quantum measurements and quantum photonic devices.

Yield of metastable atoms from a rare gas discharge in a longitudinal magnetic field

Atomic beam experiments are limited by intensity. Intensity limitations are specially critical in the measurements of metastable atoms, since their relative population is several order of magnitude smaller than the beam population. This thesis provides a method for increasing the intensity of metastable argon and neon beams effusing from a hot cathode, glow discharge by use of a longitudinal magnetic field. The argon and neon metastable atom intensities have been measured for a range of discharge pressure, voltage, and current for a magnetic field strengths from 0 to 31 mT. For both argon and neon, the metastable atom beam intensity rises to a maximum value about one order of magnitude above the zero field case. A qualitative discussion of the theory of this phenomenon is also presented.