Dallin S. Durfee

Evidence for a Critical Velocity in a Bose-Einstein Condensed Gas

We have studied dissipation in a Bose-Einstein condensed gas by moving a blue detuned laser beam through the condensate at different velocities. Strong heating was observed only above a critical velocity.

Direct, Nondestructive Observation of a Bose Condensate

The spatial observation of a Bose condensate is reported. Dispersive light scattering was used to observe the separation between the condensed and normal components of the Bose gas inside a magnetic trap. This technique is nondestructive, and about a hundred images of the same condensate can be taken. The width of the angular distribution of scattered light increased suddenly at the phase transition.

Long-Term Stability of an Area-Reversible Atom-Interferometer Sagnac Gyroscope

We report the first demonstration of a matter-wave interference gyroscope that meets both the short-term noise and long-term stability requirements for high accuracy navigation. This performance level resulted from implementation of a novel technique to precisely reverse the input axis of the gyroscope.

Fluorescence measurements of expanding strongly coupled neutral plasmas.

We report new detailed density profile measurements in expanding strongly coupled neutral calcium plasmas. Using laser-induced fluorescence techniques, we determine plasma densities in the range of 10(5) to 10(9) cm(-3) to with a time resolution limit as small as 7 ns. Strong coupling in the plasma ions is inferred directly from the fluorescence signals. Evidence for strong coupling at late times is presented, confirming a recent theoretical result.

An ultrahigh stability, low-noise laser current driver with digital control

We present a low-noise, high modulation-bandwidth design for a laser current driver with excellent long-term stability. The driver improves upon the commonly used Hall-Libbrecht design. The current driver can be operated remotely by way of a microprocessing unit, which controls the current set point digitally. This allows precise repeatability and improved accuracy and stability. It also allows the driver to be placed near the laser for reduced noise and for lower phase lag when using the modulation input. We present the theory of operation for our driver in detail, and give a thorough characterization of its stability, noise, set-point accuracy and repeatability, temperature dependence, transient response, and modulation bandwidth.

Experimental studies of Bose-Einstein condensation

We describe several experimental studies of Bose-Einstein condensation in a dilute gas of sodium atoms. These include studies of static and dynamic behavior of the condensate, and of its coherence properties.

Ultracold neutral plasma expansion in two dimensions

An isothermal model of ultracold neutral plasma expansion is extended to systems without spherical symmetry. It is used to interpret new fluorescence measurements on ultracold neutral calcium plasmas. For a self-similar expansion, the fluid equations are solved both analytically and numerically. The density and velocity solutions are used to predict fluorescence signals induced by a laser beam weakly focused into the plasma. Despite the simplicity of the model, predicted fluorescence signals reproduce major features of the experimental data.

Testing Nonclassical Theories of Electromagnetism with Ion Interferometry

We discuss using a tabletop ion interferometer to search for deviations from Coulombs inverse-square law. Such deviations would result from nonclassical effects such as a nonzero photon rest mass. We discuss the theory behind the proposed measurement, explain which fundamental, experimentally controllable parameters are the relevant figures of merit, and calculate the expected performance of such a device in terms of these parameters. The sensitivity to deviations in the exponent of the inverse-square law is predicted to be a few times 10(-22), an improvement by 5 orders of magnitude over current experiments. It could measure a nonzero photon rest mass smaller than 9 x 10(-50) grams, nearly 100 times smaller than current laboratory experiments.

BOSE-EINSTEIN CONDENSATION OF ULTRACOLD ATOMIC GASES

Bose–Einstein condensation in a dilute gas of sodium atoms has been observed. The atoms were trapped in an optically plugged magnetic trap or in a cloverleaf magnetic trap. Rf induced evaporative cooling increased the phase-space density by six orders of magnitude. We summarize the different techniques used, and discuss recent studies of properties of Bose condensates with an outlook on future developments.

Note: Updates to an ultra-low noise laser current driver

We describe updates to our current driver design allowing for higher output currents, both positive and negative currents, and updated digital interfacing to the microcontroller. We also discuss measurement of the noise spectral density of the driver with a better technique, showing that the drivers actual current noise density is about an order of magnitude lower than the upper limit we previously determined.