A distributed, graphical user interface based, computer control system for atomic physics experiments.

Atomic physics experiments often require a complex sequence of precisely timed computer controlled events. This paper describes a distributed graphical user interface-based control system designed with such experiments in mind, which makes use of off-the-shelf output hardware from National Instruments. The software makes use of a client-server separation between a user interface for sequence design and a set of output hardware servers. Output hardware servers are designed to use standard National Instruments output cards, but the client-server nature should allow this to be extended to other output hardware. Output sequences running on multiple servers and output cards can be synchronized using a shared clock. By using a field programmable gate array-generated variable frequency clock, redundant buffers can be dramatically shortened, and a time resolution of 100 ns achieved over effectively arbitrary sequence lengths.

Correlations and pair formation in a repulsively interacting Fermi gas.

A degenerate Fermi gas is rapidly quenched into the regime of strong effective repulsion near a Feshbach resonance. The spin fluctuations are monitored using speckle imaging and, contrary to several theoretical predictions, the samples remain in the paramagnetic phase for an arbitrarily large scattering length. Over a wide range of interaction strengths a rapid decay into bound pairs is observed over times on the order of 10ℏ/E(F), preventing the study of equilibrium phases of strongly repulsive fermions. Our work suggests that a Fermi gas with strong short-range repulsive interactions does not undergo a ferromagnetic phase transition.

Speckle imaging of spin fluctuations in a strongly interacting Fermi gas.

Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

Suppression of density fluctuations in a quantum degenerate Fermi gas.

We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

Amplification and front facet reflectivity of broad area lasers.

The effect of front-facet reflectivity on the amplification performance of Broad Area Laser (BAL) diodes in a double-pass configurationis studied experimentally. A method to measure the front facet reflectivities of laser diodes is generalized to BALs. The method is based on fitting a model, with front facet reflectivity as a parameter, to the threshold current vs. external feedback of the diode. Reflectivities of three BAL diodes are measured, and their amplification abilities have been assessed. The tested diodes had amplification factors of 0, 1, and 10 and front facet reflectivities of 12.7 +/-1%, 4.6 +/-0.4%, and 1.2 +/-0.2% respectively. It is concluded that a front facet modal reflectivity of less than 4.6% is necessary for a BAL to function as an amplifier.