By Fall 1999, we had decided to build a new chamber which would be the next generation of BEC production techniques. Many improvements to the BEC I and II were planned. Given some of the problems we faced in BEC II, we decided that a steel chamber with 10" ports to accomodate bucket windows for cloverleaf magnetic trap coils would be ideal chamber. The basic design is a wheel type system with flanges coming off its radii.

The buckets are larger compared to BEC I (6" inner diameter compared to 4" in BEC I), which would allow for tighter magnetic trap. The cloverleaf traps were built using square copper tubing to maximize copper per volume. It has bias tuning coils and extra coils for kicking the trap. In addition, the electrical connection for the cloverleafs allows for maximum flexibility for future changes. With maximum currents, we need to dissipate 20kW of power, which is accomplished by running 100 Psi pressurized water through the copper tubes.

By the end of January 2001, we had finally finished out the baking of the chamber and it was ready to make sodium Bose condensates. The optics and the electronics were rapidly setup such that within 15 days we have a dark-spot MOT.

On February 23rd 2001, the first BECs in this chamber were produced. Since then it has been optimized to produce stable condensates with about 10 million atoms.

The key feature of BEC III is its ability to transport Bose condensates from where it is made to an auxilliary chamber where it would be manipulated. In most of the currently working BEC machines, the studies on and with BEC are performed in the same region where the condensate is produced. This imposes severe restrictions on the accessability of the BEC and thus possible experiments. With BEC III, we have a condensate beam-line which delivers condensate atoms to various experimental platforms. This condensate transportation is accomplished using optical tweezers, i.e., an optical trap which can be moved.

The auxilliary "science chamber" is separated by a gate valve and bellows from the main chamber, which allows for us to change, add and bake out the science chamber without affecting the vacuum or the infrastructure in place on the main chamber.

The optical tweezers is formed using an infrared (1064 nm) laser light focused onto the condensate. The ir beam is filtered using a fiber, expanded using telescopes and finally a parallel beam is sent onto a 500 mm focal length lens, which is on a translation stage, "the t-stage lens". The focus of the beam from this lens is imaged onto the condensate using a pair of relay lens. As the t-stage lens is moved, the focus inside the chamber is moved, thereby the condensate which in the ir focus, is moved from the production chamber to the science chamber.

The translation stage with 2 stages of vibration isolation

In July 2001, we finally had about a million sodium condensate atoms in the science chamber using this technique.
See paper for more information.

In order to demostrate the usefulness of the transport technique, we transferred the condensate atoms from the optical tweezers into another magnetic trap formed by a Z-shaped wire in the science chamber. A wire trap, as it is called, is formed the magnetic field produced by the current flowing through the Z-shaped wire and an external bias field. The magnetic trap is an Ioffe-Pritchard type magnetic trap. We transferred condensates from the tweezers to this new trap, thereby demostrating the possibilities for future manipulation of condensates in microtraps, which can be used to study waveguide physics.
See paper for more details.

The Z-shaped wire can be seen inside the science chamber.

CURRENT STATUS:

A microtrap for future experiments has been designed and ordered. Once we have the chip, it will be put in the chamber and baked out. In addition, a new translation stage with air-bearings has been ordered and will be tested shortly.
(October 31, 2001).

THE GROUP:
This chamber was built with blood, sweat and dedication by a large group of BEC I members, including Ananth Chikkatur, Todd Gustavson, Deep Gupta, Aaron Leanhardt, Axel Gorlitz, Shin Inouye and Till Rosenband.

The current members of BEC III are: Ananth Chikkatur, Aaron Leanhardt, Yong-Il Shin, David Kielpinski, and Edem Tsikata.