Cold atoms are dancing in electric trap
Researchers at the FOM Institute for Plasmaphysics in Rijnhuizen and the Frits-Haber-Institut der Max-Planck-Gesellschaft in Berlin have been stored ultracold rubidium atoms in an atomic trap that solely uses electric fields. Such a trap is not only able to capture atoms, but also molecules. Capturing atoms in this trap is an important step forward to a combined capturing and cooling of atoms and molecules. In this way the researchers also try to cool molecules to the extremely low temperature of laser cooled atoms. By using cold atoms extreme precision can be gained in chronometry and spectroscopy. The researchers will soon have their findings published in the printed version of Physical Review Letters. Meanwhile, the on-line version is available.
Trapping atoms and molecules is of importance for studying the characteristics and interactions between particles. Scientists are capturing particles in a magnetic or electric trap. So far, they have been using magnetic traps, chiefly to capture atoms. Many atoms do have a magnetic dipole moment, but they do not have an electric dipole moment. The opposite applies to molecules and so they can be very well stored in electric traps. Such a trap enables scientists to store atoms in the lowest energy condition possible, the absolute ground state. Consequently, it is not possible to release energy at collisons between atoms and molecules in an electric trap. However, it is possible to release energy at collisons in a magnetic trap, which causes the temperature to rise.
A variable electric field
The researchers exactly used an electric field in this experiment in order to capture magnetic atoms. The electric field that is used, is so strong that even atoms without an electric dipole moment become polarized and experience strength. At first, the researchers cooled the atoms by using lasers up to ten thousandth degree above absolute zero. They kept the atoms in a magnetic field. Then, they switched off the magnetic field and applied a variable electric field. This field drives the atoms together alternately in horizontal and vertical direction. A configuration of the electric field that keeps atoms at the same time in all directions does not exist. By switching between several field configurations in the right pace, the atoms are being trapped all the same. The right pace of switching appeared to be extremely critical: for this electric trap the switching frequencies have to be between 57 and 70 Herz. The atoms are dancing because of the variable horizontal and vertical trapping fields and the shape of the atom cloud is changing in every cycle from spherical to elongated. As rubidium atoms can be very well depicted by using a laser light, the atom cloud provides the first ‘live’ pictures of the ultracold dancing movement of electric trapped particles. The next big step for the researchers is to have a try at capturing atoms and molecules at the same place and at the same time. Current experiments have been indicating that this is possible, despite the fact that atoms and molecules have different dipole moments.
References: Trapping of Rb Atoms by ac Electric Fields
Sophie Schlunk, Adela Marian, Peter Geng, Allard P. Mosk, Gerard Meijer, and Wieland Schollkopf, Phys. Rev. Lett. 98, 223002 (2007).
For more information, please contact Dr. Allard Mosk, presently working at the University of Twente, (053) 489 53 90 or (053) 489 53 92, or Professor Gerard Meijer, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlijn.