News in Brief
and of Applied Physics at Harvard. “As importantly for scientists, this is the first merging of cold-atom and nanoscale science, and it opens the door to
a new generation of cold atom experiments and
nanoscale devices.” Hau and co-authors Anne Goodsell, Trygve Ristroph, and Jene A. Golovchen- ko laser-cooled clouds of one million rubidium atoms to just a fraction of a degree above absolute zero. The physicists then launched this millimeter- long atomic cloud towards a suspended carbon nanotube, located some two centimeters away and charged to hundreds of volts. The vast majority of the atoms passed right by the wire, but those that came within a micron of it –roughly 10 atoms in every million-atom cloud – were inescapably attracted, reaching high speeds as they spiraled toward the nanotube.
“From a start at about 5 meters per second, the cold atoms reach speeds of roughly 1,200 meters per second, or more than 2,700 miles per hour, as they circle the nanotube,” says Goodsell, a gradu- ate student on the project and now a postdoctoral researcher in physics at Harvard. “As part of this tre- mendous acceleration, the temperature correspon- ding to the atoms‘ kinetic energy increases from 0.1 degrees Kelvin to thousands of degrees Kelvin in less than a microsecond.”
At this point, the speeding atoms separate into an electron and an ion rotating in parallel around the nanowire, completing each orbit in just a few trillionths of a second. The electron eventually gets sucked into the nanotube via quantum tunneling, causing its companion ion to shoot away – repelled by the strong charge of the 300-volt nanotube – at a speed of roughly 26 kilometers per second, or
10-04 :: April 2010
Launched laser-cooled atoms are captured by a single, suspended, single-wall carbon nanotube charged to hundreds of volts. A captured atom spirals towards the nanotube (white path) and reaches the environs of the tube surface, where its valence electron (yellow) tunnels into the tube. The resulting ion (purple) is ejected and de- tected, and the dynamics at the nanoscale are sensitively probed. © Anne Goodsell and Tommi Hakala/Harvard University
59,000 miles per hour. The entire experiment was conducted with great precision, allowing the scien- tists unprecedented access to both cold-atom and nanoscale processes.
Anne Goodsell, Trygve Ristroph, J. A. Golovchenko, and Lene Vestergaard Hau: Field Ionization of Cold Atoms near the Wall of a Single Carbon Nanotube, In: Physical Review Letters, Vol. 104(2010), Issue 13, Article 133002 [4 pages], DOI:10.1103/PhysRevLett.104.133002: http://dx.doi.org/10.1103/PhysRevLett.104.133002