Phase Space Manipulation of Cold Free Radical OH Molecules

We report bunching, slowing, and acceleration of a supersonically cooled beam of diatomic hydroxyl radicals (OH). \textit{In situ} observation of laser-induced fluorescence along the beam propagation path allows for detailed characterization of longitudinal phase-space manipulation of OH molecules through the Stark effect by precisely sequenced inhomogeneous electric fields.Comment: 5 pages, 4 color figure

Prospects for a mHz-linewidth laser

We propose a new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultra-narrow clock transition into the mode of a high Q-resonator. The resultant optical radiation has an extremely narrow linewidth in the mHz range, even smaller than that of the clock transition itself due to collective effects. A power level of order $10^{-12}W$ is possible, sufficient for phase-locking a slave optical local oscillator. Realizing this light source has the potential to improve the stability of the best clocks by two orders of magnitude.Comment: minor revisions + shortening; factor 2 algebra mistake correcte

Hofstadter-type energy spectra in lateral superlattices defined by periodic magnetic and electrostatic fields

We calculate the energy spectrum of an electron moving in a two-dimensional lattice which is defined by an electric potential and an applied perpendicular magnetic field modulated by a periodic surface magnetization. The spatial direction of this magnetization introduces complex phases into the Fourier coefficients of the magnetic field. We investigate the effect of the relative phases between electric and magnetic modulation on band width and internal structure of the Landau levels.Comment: 5 LaTeX pages with one gif figure to appear in Phys. Rev.

The Cone-Like H-alpha Nebula in NGC 4945: A Galactic Superwind Bow Shock ?

We find that a non-axisymmetric bow shock model, with an appropriate choice of parameters, could fit the line splitting velocity field of the cone-like H$\alpha$ nebula in NGC 4945 better than a canonical cone model. Meanwhile, the bow shock model could also reproduce the morphology of the H$\alpha$ nebula. The bow shock results from the interaction of the galactic superwinds with a giant HII region. It is implied that the starburst ring or disk around the galactic nucleus should be generating strong winds, and the bright H$\alpha$ knot northwest of the nucleus be suffering an anisotropic mass loss process.Comment: 14 pages, aasms4.sty, 3 figures not included (available upon request) To appear in ApJ Letters. email chy, [email protected]

Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant

We report precise measurements of ground-state, $\lambda$-doublet microwave transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold molecules produced by a Stark decelerator we have improved over the precision of the previous best measurement by twenty-five-fold for the F' = 2 $\to$ F = 2 transition, yielding (1 667 358 996 $\pm$ 4) Hz, and by ten-fold for the F' = 1 $\to$ F = 1 transition, yielding (1 665 401 803 $\pm$ 12) Hz. Comparing these laboratory frequencies to those from OH megamasers in interstellar space will allow a sensitivity of 1 ppm for $\Delta\alpha/\alpha$ over $\sim$$10^{10}$ years.Comment: This version corrects minor typos in the Zeeman shift discussio

Planar cyclotron motion in unidirectional superlattices defined by strong magnetic and electric fields: Traces of classical orbits in the energy spectrum

We compare the quantum and the classical description of the two-dimensional motion of electrons subjected to a perpendicular magnetic field and a one-dimensional lateral superlattice defined by spatially periodic magnetic and electric fields of large amplitudes. We explain in detail the complicated energy spectra, consisting of superimposed branches of strong and of weak dispersion, by the correspondence between the respective eigenstates and the ``channeled'' and ``drifting'' orbits of the classical description.Comment: 11 pages, 11 figures, to appear in Physical Review