62

nanotimes

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 Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87