Scientists develop method for precisely controlling electrons

VIENNA, Nov. 15 (UPI) -- Electrons are unwieldy, constantly moving. Scientists can only approximate their position and movement within quantum systems. In other words, they're not easily corralled.

But scientists at TU Wien and the University of Erlangen-Nuremberg say they're making progress, having found a way to render some control over the elusive atomic particle.

Researchers in Austria and Germany developed a method for more precisely controlling the emission of electrons through the tiny metal tip of an electron microscope. The method involves the use of two different laser pulses to quickly switch on and off the flow of electrons.

"The basic idea resembles a lightning rod," Christoph Lemell, a researcher at TU Wien, said in a news release. "The electrical field around a needle is always strongest right at the tip. That's why the lightning always strikes the tip of a rod, and for the same reason, electrons leave a needle right at the tip."

The combination of the two pulsing lasers and a tiny metal tip, measuring just a few nanometers across, offers scientists the ability to control electrons in time and space.

"Two different laser pulses are fired at the metal tip," said Florian Libisch, another TU Wien researcher. "The colors of these two lasers are chosen such that the photons of one laser have exactly twice the energy of the other laser's photons. Also, it is important to ensure that both light waves oscillate in perfect synchronicity."

Scientists theorized the time delay between the two laser pulses would act as a switch, turning on and off the emission of electrons. Testing proved the theory correct.

Photons from the two laser pulses offer electrons two ways to gain the energy necessary to leave the metal tip of the electron microscope. An electron can be compelled to make the jump by absorbing four electrons from the low-energy pulse, or one photon from the high-energy laser and two from the low-energy pulse.

"Much like a particle in a double slit experiment, which travels on two different paths at the same time, the electron can take part in two different processes at the same time," explained TU Wien scientist Joachim Burgdörfer. "Nature does not have to pick one the two possibilities -- both are equally real and interfere which each other."

Scientists can tune the laser to amplify the two quantum processes, encouraging electron emission, or to encourage quantum interference, thus limiting emission.

A similar technique could be used to control X-ray emission.

"Innovative x-ray sources are already being built, using arrays of narrow metal tips as electron sources," added Lemell. "With our new method, these nano tips could be triggered in exactly the right way so that coherent x-ray radiation is produced."

Researchers detailed their new methodology in the journal Physical Review Letters.