Friday, September 24, 2010

Dynamics of a tunable superfluid junction

L. J. LeBlanc, A. B. Bardon, J. McKeever, M. H. T. Extavour, D. Jervis, J. H. Thywissen, F. Piazza, A. Smerzi

We study the population dynamics of a Bose-Einstein condensate in a double-well potential with tunable barrier height. In the regime of weak inter-well coupling, we observe Josephson plasma oscillations as expected. However, in the strong-coupling regime, a second frequency enters the dynamics. We explain the amplitude, frequency, and nature of these two modes by with Gross-Pitaevskii calculations throughout the weak- to strong-coupling crossover. Our results interpolate between two standard paradigms of superfluidity: hydrodynamics and Josephson dynamics.

**Groupmeeting by Lindsay LeBlanc, September 22nd, 2010**

Simple approach to the relation between laser frequency noise and laser line shape

Gianni Di Domenico, St├ęphane Schilt, and Pierre Thomann

Frequency fluctuations of lasers cause a broadening of their line shapes. Although the relation between the frequency noise spectrum and the laser line shape has been studied extensively, no simple expression exists to evaluate the laser linewidth for frequency noise spectra that does not follow a power law. We present a simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities.

Thermometry with spin-dependent lattices

D McKay and B DeMarco

We propose a method for measuring the temperature of strongly correlated phases of ultracold atom gases confined in spin-dependent optical lattices. In this technique, a small number of 'impurity' atoms—trapped in a state that does not experience the lattice potential—are in thermal contact with atoms bound to the lattice. The impurity serves as a thermometer for the system because its temperature can be straightforwardly measured using time-of-flight expansion velocity. This technique may be useful for resolving many open questions regarding thermalization in these isolated systems. We discuss the theory behind this method and demonstrate proof-of-principle experiments, including the first realization of a three-dimensional (3D) spin-dependent lattice in the strongly correlated regime.

**Groupmeeting by Dave McKay, September 8th, 2010**

Wednesday, September 1, 2010

Photons: Still Bosons

D. English, V. V. Yashchuk, D. Budker

Using Bose-Einstein-statistics-forbidden two-photon excitation in atomic barium, we have limited the rate of statistics-violating transitions, as a fraction $\nu$ of an equivalent statistics-allowed transition rate, to $\nu<4.0\times10^{-11}$ at the 90% confidence level. This is an improvement of more than three orders of magnitude over the best previous result. Additionally, hyperfine-interaction enabling of the forbidden transition has been observed, to our knowledge, for the first time.