Portland, Ore. - A 1.5-GHz silicon "comb" that is said to be the world's fastest nanoscale electromechanical system (NEMS) is nevertheless huge on the quantum scale: The oscillation of its teeth exhibit the world's biggest quantum motion. According to the research project team, headed by Boston University professor Pritiraj Mohanty, the teeth of the comb exhibit quantum-mechanical motion by jumping between two discrete positions without passing through the physical space between them.

"We believe that our system is truly a macroscopic quantum system, [but since] it's a new phenomenon, it's best not to be guided by expectations based on conventional wisdom. The philosophy here is to let the data speak for itself," said Alexei Gaidarzhy, one of the principal researchers in Mohanty's group. Other researchers in Mohanty's group included Guiti Zolfagharkhani, a graduate student, and Robert Badzey, a post-doctoral Fellow in Boston University's Physics Department.

EEs are familiar with quantum tunneling of electrons, whereby they disappear from the semiconductor side of a nanometer ultrathin oxide and reappear on its metal side without actually passing through the oxide itself. But this phenomenon, as with all other quantum-mechanical behavior to date, has occurred on a microscopic scale.

The 10.7-micron-long silicon bar, on the other hand, is positively macroscopic compared with the size of a single tunneling electron. In particular, the silicon comb has more than 1 billion atoms (each one of which has electrons orbiting it), prompting the team's claim to the world's biggest quantum motion.

1.02-GHz reading
To back up their claim that their NEMS is the world's fastest, the Boston University researchers cite a previous research group that claimed to have pegged their NEMS as the world's fastest, at 1.02 GHz.

To get the silicon bar to oscillate at 1.5 GHz, the team had to refrigerate it down to within 110 millikelvin above absolute zero. At those temperatures, quantum-mechanical oscillation enabled the bar to jump between two discrete positions without occupying the physical space in between. A copper-walled and -floored room shielded the device from all types of electromagnetic radiation. Shock absorbers isolated the platform from the vibrations of subway trains in Boston.

The silicon bar was constructed with two rows of antenna-like protrusions along each side, making it look like a comb with rows of teeth on each side. The teeth of the comb were 500 nanometers long and protruded 200 nm along each side. When the bar started to oscillate, each tooth vibrated in concert with the others-jumping between two positions only a femtometer apart. The concerted motion, however, makes the entire comb oscillate at the same frequency, but at a more measurable displacement of 0.1 picometer-a hundredfold increase in mechanical amplitude.

The group speculates that such quantum-mechanical devices could eventually be integrated into normal chips the way quantum tunneling devices are today, as well as into advanced computer designs based on quantum computing principles.

The research was supported by funds from the National Science Foundation, the U.S. Department of Defense, the American Chemical Society's Petroleum Research Fund and the Sloan Foundation.