Princeton University’s tiny microwave laser is being called a “maser” while being powered by single electrons.

Technically, the “maser” is being powered by single electrons that are tunneled through quantum dots, and requires about one-billionth of the electric current one would need to make toast in the morning. The researchers built the tiny laser to gain a better understanding of how quantum dots might be used in the production of quantum computers.

Rice-Sized Laser? Wrong, It's a "Maser"

The researchers from Princeton University recently had their findings published in the journal Science.

“It is basically as small as you can go with these single-electron devices,” said Jason Petta, an associate professor of physics at Princeton who led the study.

Unintentional laser

While the researchers did indeed build a “maser,” it was not their intention when they began work. The project was laid-out in order to learn more about qubits, or double quantum dots, which are the basic units used in quantum computers. “The goal was to get the double quantum dots to communicate with each other,” said Yinyu Liu, a physics graduate student in Petta’s laboratory who joined the study along with two others including an associate research scholar and a postdoctoral researcher.

The “double dots” were designed to emit light particles, photons, from a higher energy level to a lower one in order to bridge the double dot transferring one electron with each trip. “It is like a line of people crossing a wide stream by leaping onto a rock so small that it can only hold one person,” explained Petta. “They are forced to cross the stream one at a time. These double quantum dots are zero-dimensional as far as the electrons are concerned—they are trapped in all three spatial dimensions.”

Construction of the “maser”

The dots were made of a semiconductor material known as indium arsenide that was fashioned into nanowires with a diameter of roughly 50 nanometers. The wires were then meshed with even smaller wires to create a gate and regulator for the electrons.

Once the “maser” was activated, electrons queued-up single file, through the double dots, which then saw them emitting microwave photons. The photons were then bounced between two mirrors on either end of the 6 millimeter cavity between two quantum dots creating a coherent beam of light in the microwave spectrum.

Unlike semiconductor lasers whose frequency is set during the manufacturing process, the maser has the ability to produce light at prescribed frequencies after construction.