System Bits: June 9

Optical constraints
Stanford University researchers have discovered strong constraints to optical data transmission but hope it can guide future research in this area.

As a reminder, optics, a form of data transmission that utilizes beams of light, has the promise to outperform the beams of electrons that drive computers or smartphones. And as engineers have long looked for a way to miniaturize optical technology, already present in today’s fiber-optic cables, they can also bring the speed and efficiency of light-based data transmission to a computer chip.

Now, however, Stanford researchers have detailed a strong theoretical limitation to what was long hoped to be a simple, promising device that would permit one-way optical data transmission on a computer chip.

Stanford electrical engineering Professor Shanhui Fan and graduate student Yu “Jerry” Shi discuss their findings in a paper published in the journal Nature Photonics. In the short term, they think this may be disappointing to some engineers but ultimately may guide researchers searching for ways to build a one-way street for light on a computer chip.

Vanishing friction
According to physicists at MIT, friction is all around us, working against the motion of tires on pavement, the scrawl of a pen across paper, and even the flow of proteins through the bloodstream. Whenever two surfaces come in contact, there is friction, except in very special cases where friction essentially vanishes — a phenomenon, known as “superlubricity,” in which surfaces simply slide over each other without resistance.

Now, they’ve developed an experimental technique to simulate friction at the nanoscale in order to directly observe individual atoms at the interface of two surfaces and manipulate their arrangement, tuning the amount of friction between the surfaces. By changing the spacing of atoms on one surface, they observed a point at which friction disappears.

Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, says the ability to tune friction would be helpful in developing nanomachines — tiny robots built from components the size of single molecules. Vuletic says that at the nanoscale, friction may exact a greater force — for instance, creating wear and tear on tiny motors much faster than occurs at larger scales.

“There’s a big effort to understand friction and control it, because it’s one of the limiting factors for nanomachines, but there has been relatively little progress in actually controlling friction at any scale,” Vuletic says. “What is new in our system is, for the first time on the atomic scale, we can see this transition from friction to superlubricity.”

A new technique tunes friction between two surfaces, to the point where friction can vanish. MIT researchers developed a frictional interface at the atomic level. The blue corrugated surface represents an optical lattice; the red balls represent ions; the springs between them represent Coulomb forces between ions. By tuning the spacing of the ion crystal surface above to mismatch the bottom corrugated surface, friction disappears. The ions smoothly slide along the surface in a caterpillar-like motion. This discovery could aid in developing nanomachines, built from components the size of single molecules. (Source: MIT)