‘Traffic light’ stops quantum waves in their tracks

(Credit: Tim Gouw/Unsplash)

A “traffic light” that can bring quantum waves to a halt could be key to harnessing the potential of the atomic world, researchers report.

Their findings could eventually lead to breakthroughs in computing, medicine, cryptography, materials science, and other applications.

“It’s an area of research of immense importance,” says Jon Bird, professor and chair in the electrical engineering department in the School of Engineering and Applied Sciences at the University at Buffalo and co-lead author of a study in the journal Physical Review Letters that describes the work.

Directing quantum waves

Researchers are working to better understand the behavior of electrons, as well as find new ways to manipulate them.

In the study, the team “used the very atoms that make up the crystal structure of the semiconductor materials that we study to either impede the passage of electrons, or to allow them to pass freely, essentially making a ‘traffic light’ for these quantum particles. We do this by ‘shaking’ these atoms controllably, through the application of small electrical signals to our devices,” says Bird.

The researchers isolated a specially built nanoconductor at an extremely cold temperature‚ÄĒminus 273 degrees Celsius (523.4 degrees Fahrenheit). Under such conditions, in this ultra-small device, electrons exhibit a wavelike nature.

In other words, they behave more like ripples on the surface of a pond as opposed to point-like particles, which are often described as billiard-ball like objects that bound around in straight lines.

“Much like light, or waves in the ocean, these quantum waves can behave in ways that we would not expect for particles. They can bend around corners, for example, and the challenge is to develop techniques to control, or steer, them,” says Han.

In the study, the researchers achieved this by applying a small amount of voltage to the conductor, thereby allowing them to shake its atoms in a controllable fashion. As the atoms were made to shake more strongly, they provided a greater source of resistance to the quantum waves, which blocked the waves from passing through the conductor.

“This is what we call a quantum point contact. You can think of it as a traffic light. Only instead of stopping automobiles at an intersection, we’ve demonstrated the ability to control the transmission of electron waves in a confined system by externally shaking the atoms in that system,” says Han.

Future computers

The ability to control subatomic particles such as electrons and photons is key to the development of quantum technologies, especially quantum computers.

Traditional computers process information, or bits, in binary code, meaning they store data and perform calculations by assigning values of “one” or “zero.” Quantum computers, which IBM, Google, and other firms are developing, work with “qubits” that can represent ones and zeros at the same time.

In theory, this approach could lead to much more powerful computers than what exist today. In turn, that would create large economic and national security advantages.

The new research provides a foundational-level implementation of the techniques that are necessary to control quantum waves at the microscopic scale, making these technological advancements a possibility, Bird says.

Additional coauthors are from the University at Buffalo, Sandia National Laboratories, and the Korea Institute for Advanced Study.

The US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering supported the research.

Source: University at Buffalo