Molecules teach the teachers

Controlling particles with quantum properties that defy classical mechanics, such as atoms and molecules, is similar to trying to control wine sloshing in a glass.

Bucksbaum (Photo courtesy Philip Bucksbaum)

Philip H. Bucksbaum, the Peter Franken Distinguished University Professor of Physics, says scientists sometimes turn the tables and rely on the molecule to teach the experimenter the best way to achieve the desired result.

"We're finding out how to control a molecule on the quantum level by asking it nicely," Bucksbaum says. "The Ultrafast Control of Atoms and Molecules" will be the subject of Bucksbaum's Distinguished University Professorship lecture at 4 p.m. Feb. 7 in the Rackham Amphitheatre.

"There is a real difficulty in controlling things with quantum properties," Bucksbaum says. "To deal with this challenge we're trying to develop different ways to do these investigations. One new way of science experiments is one where we don't actually plan the experiment in advance, but rather rely on the molecule itself to design the experiment for us."

Bucksbaum says scientists can use lasers that generate ultrafast pulses of light to control molecules, but the problem is scientists don't know how the molecules will react to different colors and intensities of light. The confusion happens because scientists haven't decoded the quantum mechanical motions of these tiniest of particles, which are far more complex than classical behavior, he says.

"So, what you do is build an instrument that can produce light in as many different ways as possible" and that also can evaluate performance very fast, he says. For instance, an entire experiment could occur in 1/1000 of a second.

Then, scientists randomly select experiments to perform. Some won't work, and some will work well, Bucksbaum says. With this type of speed, in 20 minutes scientists can perform millions of experiments, he adds. The most successful characteristics are built into each new generation of experiments, and the learning feedback loop continues until scientists are able to get the desired results by combining the best characteristics. In short, he says, they back into the experiments in order to tease out the best method.

"It was taught to you, in a pretty direct way, by the molecule itself," Bucksbaum says. "I think of it as the experimenter is the student being taught by the molecule."

Bucksbaum also will explore how researchers build these ultrafast lasers, which can manipulate light 10,000 times faster than the chemical reactions that occur in the molecules in our bodies.

"Your eye can't blink that fast," Bucksbaum says. "Your fingers can't snap that fast, so how do you turn a light on and off that fast? That's an interesting question. And how do you know that you did it?"