Graduate Student Sarah Thompson, Research Associate Eleanor Hodby, and Fellow Carl Wieman have come up with a novel way to assemble Feshbach molecules from a cloud of ultracold atoms. The molecules consist of very weakly bound atoms that are about as far apart in the molecular state as they are in the atom cloud from which they are formed. Understanding the properties of these molecules promises to help researchers better understand Bose-Einstein condensation and ultracold fermionic systems.
Thompson and her colleagues discovered they could cause Feshbach molecules to form by exposing an ultracold cloud of rubidium atoms to an oscillating magnetic field whose frequency was near that of the atoms' binding energy. The figure on the right shows how photons from the magnetic field stimulate atom pairs to emit a photon and thereby decay into the lower energy molecular state.
The researchers expect to be able to obtain a precise measurement of the molecular binding energy of Feshbach molecules made in this way by incrementally changing the applied frequency and looking at the number of molecules produced. The new technique will likely be an important spectroscopic tool to probe the creation and properties of molecules formed under ultracold conditions. It outperforms other methods for making Feshbach molecules from bosonic atoms (atoms with a spin state of zero) because it causes minimal heating of the atom cloud. Until now, such heating had limited the number of molecules that could be formed from an ultracold atom cloud of bosons.
The researchers reported their findings in an article in the November 4, 2005, issue of Physical Review Letters. - Julie Phillips