Chromium condensate makes its mark
Mar 10, 2005
Physicists in Germany have created a Bose-Einstein condensate from a gas of chromium atoms for the first time. Unlike all the other elements that have previously been condensed, chromium has a very large magnetic dipole moment. Tilman Pfau and colleagues at the University of Stuttgart say that their novel condensate will therefore allow scientists to study dipolar interactions in quantum degenerate gases, and might also find practical applications in nanolithography (A Griesmaier et al. 2005 arXiv.org/abs/cond-mat/0503044).
Bose-Einstein condensation occurs when a gas of atoms is cooled to such ultra-low temperatures that the de Broglie wavelength of the atoms becomes comparable to the distance between them. As a result, the atoms collapse into the same quantum ground state. The first Bose condensate was created ten years ago with rubidium atoms, and researchers have since created condensates from eight other elements, including the alkali atoms sodium, lithium, potassium and caesium.
The properties of a Bose-Einstein condensate (BEC) depend on the interactions between its individual atoms. The strength of the magnetic dipole-dipole interaction in BECs made from alkali atoms is tiny, but the corresponding value for chromium -- which is a transition metal -- is 36 times higher. This is because chromium has a unique electronic structure: the valance shell of its ground state contains six electrons whose spins are aligned parallel to one another. As a result, chromium has a total electronic spin number of three and a very large magnetic moment of 6 Bohr magnetons.
Physicists will therefore be able to investigate not only short-range dipole-dipole interactions -- using a so-called Fesbach resonance -- but long-range interactions too. Furthermore, the chromium condensate will allow researchers to study many dipolar phenomena and new kinds of quantum phase transitions that have been predicted by theory.
Pfau and colleagues were able to produce condensates with up to 100,000 chromium atoms at a temperature of 625 nanokelvin, which they say provides an excellent base for several promising experiments. In particular, chromium is routinely used as a mask in atom lithography, which means that coherent sources of chromium atoms such as BECs could have applications in nanostructuring, and might even allow for controlled deposition of single atoms on a substrate.
About the author
Belle Dumé is Science Writer at PhysicsWeb