A Spinless BEC

A spinless BEC, a Bose-Einstein condensate that is insensitive to any external magnetic field, has been created by researchers at Kyoto University (contact Yosuke Takasu or Yoshiro Takahashi), potentially offering a route to improved atomic clocks, more precise atom interferometry, and more highly controlled means of depositing atoms on surfaces. In all previous Bose-Einstein condensates, the raw ingredients have either been alkali metals (such as rubidium and cesium) or helium, all of which have been sensitive to magnetic fields. In contrast, the researchers decided to make a BEC of ytterbium (Yb), a rare-earth element that has two outer (valence) electrons, whose "spins" determine the atom's response to a magnetic field. When the spins of Yb's two electrons are in opposite directions, the total spin is zero and the atom assumes a "singlet" state, in which it is unresponsive to a magnetic field. In their setup, the researchers trap approximately 1 million Yb atoms in the singlet state with light beams. The hotter atoms evaporate away, leaving a chilly gas cloud of about 5000 atoms that form a BEC at temperatures of below 790 nanokelvins. Since the Yb BEC is insensitive to stray magnetic fields in its surroundings, it may allow for more precise atomic deposition and atom interferometry. Moreover, the very heavy mass of Yb compared to other BEC atoms means that certain fundamental physics effects, such as atomic parity violation and time symmetry violation, are more pronounced, making a Yb BEC desirable for such studies. Furthermore, lasers interacting with the Yb atoms can be tuned to a very narrow frequency range, potentially enabling a Yb BEC to be the basis of an atomic clock with unprecedented precision. Finally, the many stable isotopes of Yb (5 are bosons, 2 are fermions) facilitates the possibility of creating a BEC and a Fermi degenerate gas in the same cloud. (Takasu et al., Physical Review Letters, 25 July 2003)