It may seem like a work of science fiction but a group of researchers has managed to develop a laser that is no bigger than a grain of rice and uses only a billionth of the electric current used for powering a hair dryer.

Jason Petta, a physics professor from Princeton University, and colleagues have created the device that they say is another step toward building quantum computing systems that use semiconductor materials.

The tiny microwave laser, also known as maser, is powered by single electrons that tunnel through artificial atoms called quantum dots and exhibit the fundamental interaction between moving electrons and light.

The researchers built the maser while investigating ways on how to use quantum dots. These artificial atoms are bits of semiconductor materials called indium arsenide, acting like single atoms serving as components for quantum computers.

Petta and colleagues created the maser using thin nanowires to link up pairs of quantum dots then placed two of these double quantum dots, which were six millimeters apart, inside a small cavity that was made from the superconductor material niobium and had mirrors on both sides. Once the device was connected to a battery, the electrons started.

The electrons flowed through the quantum dots then emitted photons in the range of a microwave, as they transitioned from a higher energy state to a lower one, after which photons bounced off the mirrors to generate a focused microwave energy.

"The double quantum dot allows them full control over the motion of even a single electron, and in return they show how the coherent microwave field is created and amplified. Learning to control these fundamental light-matter interaction processes will help in the future development of light sources," Claire Gmachl from Princeton University commented on the paper describing the researchers' work.

The researchers look forward to using the double quantum dots as quantum bits. Also known as qubits, these are the basic units of information in quantum computers. The challenges in quantum computing involve coupling quantum bits so these can be utilized to transmit information over large distances. The researchers said that quantum dots may address this problem.

"Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication," Petta and colleagues wrote in their paper published in Science on Jan. 16.

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