Breakthrough Rice-Sized Laser is Powered by Tiny Electrons

Scientists have built a rice grain-sized laser powered by single electrons tunneling through artificial atoms known as quantum dots that could be a breakthrough in laser science. The tiny laser, now called a "maser," is a demonstration of the fundamental interactions between light and moving electrons.

The researchers created the new device while exploring how to use quantum dots, which are bits of semiconductor material that act like single atoms, as components for quantum computers. These bits are known as qubits, and are basic units of information in quantum computers.

"The goal was to get the double quantum dots to communicate with each other," said Yinyu Liu, one of the researchers, in a news release.

Each double quantum dot can only transfer one electron at a time. That's why they fabricated the double quantum dots from extremely thin nanowires made of a semiconductor material called indium arsenide. Then, they patterned the indium arsenide wires over other even smaller metal wires that act as gate electrodes, which control the energy levels in the dots.

In order to construct the maser, the scientists placed the two double dots in a cavity made of a superconducting material, niobium, which requires a temperature near absolute zero. When the device was switched on, electrons flowed single-file through each double quantum dot, causing them to emit photons in the microwave region of the spectrum.

What makes the new maser especially useful is that energy levels inside the dots can be fine-tuned to produce light at other frequencies, which cannot be done with other semiconductor lasers in which the frequency is fixed during manufacturing. Lasers are used in communications, sensing, medicine and other applications, which makes this study huge in terms of laser research.

The findings are published in the journal Science.

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