Nathaniel Brahms

High-Flux Beam Source for Cold, Slow Atoms or Molecules

We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.

Tunable cavity optomechanics with ultracold atoms.

We present an atom-chip-based realization of quantum cavity optomechanics with cold atoms localized within a Fabry-Perot cavity. Effective subwavelength positioning of the atomic ensemble allows for tuning the linear and quadratic optomechanical coupling parameters, varying the sensitivity to the displacement and strain of a compressible gaseous medium. We observe effects of such tuning on cavity optical nonlinearity and optomechanical frequency shifts, providing their first characterization in the quadratic-coupling regime.

Buffer gas cooling and trapping of atoms with small effective magnetic moments

We have extended buffer gas cooling to trap atoms with small effective magnetic moments μeff. For μeff ≥ 3μB, 1012 atoms were buffer gas cooled, trapped, and thermally isolated in ultra high vacuum with roughly unit efficiency. For μeff < 3μB, the fraction of atoms remaining after full thermal isolation was limited by two processes: wind from the rapid removal of the buffer gas and desorbing helium films. In our current apparatus we trap atoms with μeff ≥ 1μB, and thermally isolate atoms with μeff ≥ 1.8μB. This triples the number of atomic species which can be buffer gas cooled and trapped in thermal isolation. Extrapolation of our results and simulations of the loss processes indicate that it is possible to trap and evaporatively cool 1μB atoms using buffer gas cooling.