Kevin L. Moore

Cavity Nonlinear Optics at Low Photon Numbers from Collective Atomic Motion

We report on Kerr nonlinearity and dispersive optical bistability of a Fabry-Perot optical resonator due to the displacement of ultracold atoms trapped within. In the driven resonator, such collective motion is induced by optical forces acting upon up to 10(5) 87Rb atoms prepared in the lowest band of a one-dimensional intracavity optical lattice. The longevity of atomic motional coherence allows for strongly nonlinear optics at extremely low cavity photon numbers, as demonstrated by the observation of both branches of optical bistability at photon numbers below unity.

Bose-Einstein Condensation in a Circular Waveguide

We have produced Bose-Einstein condensates in a ring-shaped magnetic waveguide. The few-millimeter diameter, nonzero-bias ring is formed from a time-averaged quadrupole ring. Condensates that propagate around the ring make several revolutions within the time it takes for them to expand to fill the ring. The ring shape is ideally suited for studies of vorticity in a multiply connected geometry and is promising as a rotation sensor.

Direct nondestructive imaging of magnetization in a spin-1 bose-einstein gas

Polarization-dependent phase-contrast imaging is used to resolve the spatial magnetization profile of an optically trapped ultracold gas. This probe is applied to Larmor precession of degenerate and nondegenerate spin-1 87Rb gases. Transverse magnetization of the Bose-Einstein condensate persists for the condensate lifetime, with a spatial response to magnetic field inhomogeneities consistent with a mean-field model of interactions. In comparison, the magnetization of the non-condensed gas decoheres rapidly. Rotational symmetry implies that the Larmor frequency of a spinor condensate be density independent, and thus suitable for precise magnetometry with high spatial resolution.

Collimated, single-pass atom source from a pulsed alkali metal dispenser for laser-cooling experiments

We have developed an improved scheme for loading atoms into a magneto-optical trap (MOT) from a directed rubidium alkali metal dispenser in <10−10Torr ultrahigh vacuum conditions. A current-driven dispenser was surrounded with a cold absorbing “shroud” held at ⩽0°C, pumping rubidium atoms not directed into the MOT. This nearly eliminates background atoms and reduces the detrimental rise in pressure normally associated with these devices. The system can be well-described as a current-controlled, rapidly switched, two-temperature thermal beam, and was used to load a MOT with 3×108atoms.

BAYESIAN EVOLUTION MODELS FOR JUPITER WITH HELIUM RAIN AND DOUBLE-DIFFUSIVE CONVECTION

Hydrogen and helium demix when sufficiently cool, and this bears on the evolution of all giant planets at large separations at or below roughly a Jupiter mass. We model the thermal evolution of Jupiter, including its evolving helium distribution following results of ab initio simulations for helium immiscibility in metallic hydrogen. After 4 Gyr of homogeneous evolution, differentiation establishes a thin helium gradient below 1 Mbar that dynamically stabilizes the fluid to convection. The region undergoes overstable double-diffusive convection (ODDC), whose weak heat transport maintains a superadiabatic temperature gradient. With a generic parameterization for the ODDC efficiency, the models can reconcile Jupiters intrinsix flux, atmospheric helium content, and radius at the age of the solar system if the Lorenzen et al. H–He phase diagram is translated to lower temperatures. We cast the evolutionary models in an MCMC framework to explore tens of thousands of evolutionary sequences, retrieving probability distributions for the total heavy-element mass, the superadiabaticity of the temperature gradient due to ODDC, and the phase diagram perturbation. The adopted SCvH-I equation of state (EOS) favors inefficient ODDC such that a thermal boundary layer is formed, allowing the molecular envelope to cool rapidly while the deeper interior actually heats up over time. If the overall cooling time is modulated with an additional free parameter to imitate the effect of a colder or warmer EOS, the models favor those that are colder than SCvH-I. In this case the superadiabaticity is modest and warming and cooling deep interiors are equally likely.

Measurement of Intracavity Quantum Fluctuations of Light Using an Atomic Fluctuation Bolometer

The spectral noise power of photon number fluctuations inside a driven high-finesse Fabry-Perot optical resonator is measured through the resonator-enhanced momentum diffusion of ultracold atoms trapped within. Light-induced heating of the trapped atoms is quantified by their rate of Evaporation from a finite-depth intra cavity optical trap. The relevance of cavity-enhanced momentum diffusion to cavity-enhanced measurements of atomic ensembles is discussed.

QUANTUM MICRO-MECHANICS WITH ULTRACOLD ATOMS

In many experiments isolated atoms and ions have been inserted into high-finesse optical resonators for the study of fundamental quantum optics and quantum information. Here, we introduce another application of such a system, as the realization of cavity optomechanics where the collective motion of an atomic ensemble serves the role of a moveable optical element in an optical resonator. Compared with other optomechanical systems, such as those incorporating nanofabricated cantilevers or the large cavity mirrors of gravitational observatories, our cold-atom realization offers direct access to the quantum regime. We describe experimental investigations of optomechanical effects, such as the bistability of collective atomic motion and the first quantification of measurement backaction for a macroscopic object, and discuss future directions for this nascent field.

Direct, non-destructive imaging of magnetization in a spin-1 bose gas

Polarization-dependent phase-contrast imaging is used to spatially resolve the magnetization of an optically trapped degenerate and nondegenerate spin-1 Rb gases. Transverse magnetization of the Bose-Einstein condensate persists for the condensate lifetime, while the noncondensed gas decoheres rapidly. Quantum fluids with a spin degree of freedom have been of longstanding interest, stimulated both by the complex phenomenology of superfluid [1] and by p-wave superconductivity [2]. Advances in ultracold atomic physics have now led to the creation of novel multicomponent quantum fluids including pseudospin-1/2 Bose-Einstein condensates (BECs) [3] and spin-1 and -2 condensates of Na [4,5] and Rb [6-8]. The internal state of a multi-component system is characterized by the populations in each of the components and the coherences among them. However, in all previous studies of the spin-1 or spin-2 spinor condensates, while the populations in each magnetic sublevel were measured, no information was obtained regarding the coherence between overlapping populations [4,6-10]. Moreover, although spatial patterns of longitudinal magnetization have been reconstructed from images of freely expanding spinor gases, the expansion process severely limits the resolution obtainable [9,11,12]. In this work, we exploit atomic birefringence to image the magnetization of an ultracold spin-1 Bose gas non-destructively with high spatial resolution. By varying the orientation of an applied magnetic field with respect to our imaging axis, we measure either longitudinal magnetization, which derives from the static populations in each of the magnetic sublevels, or transverse magnetization, which derives from time-varying ∆m=1 coherences. This probe is used to observe Larmor precession in both degenerate and non-degenerate spinor Bose gases. In particular, optical characterization of Larmor precession in a BEC provides a novel probe of the relative phases between condensates in different internal states with excellent temporal and spatial resolution (see Refs.[13] for other recent measurements of

Probing the Quantum State of a Guided Atom Laser Pulse

We describe bichromatic superradiant pump-probe spectroscopy as a tomographic probe of the Wigner function of a dispersing particle beam. We employed this technique to characterize the quantum state of an ultracold atomic beam, derived from a 87Rb Bose-Einstein condensate, as it propagated in a 2.5 mm diameter circular waveguide. Our measurements place an upper bound on the longitudinal phase space area occupied by the 3 x 10(5) atom beam of 9(1)Plancks constant and a lower bound on the coherence length of L>or=13(1) microm. These results are consistent with full quantum degeneracy after multiple orbits around the waveguide.

Empirical bounds for the ionizing fluxes of Wolf-Rayet stars

Hα photometry and spectroscopic data have been obtained for 10 Wolf-Rayet nebulae, representing a wide variety of WN spectral types. We use these data to constrain the ionizing flux of the exciting Wolf-Rayet star, calculating lower bounds for the Lyman continuum flux (Q0) and for the He0- and He+-ionizing fluxes (Q1 and Q2). We find that Q0 appears independent of WN spectral type, and lower bound estimates tend to cluster around 48 dex. Finally, we discuss the effects of potential shock excitation and density bounding on these nebulae and compare our results to recent models. Our results are consistent with the predictions of line-blanketed ISA-wind models and nonblanketed CMFGEN models but are consistent with only some of the line-blanketed CMFGEN models.