Quantum computing has taken one more step closer, say researchers at Princeton University who've created a laser the size of a grain of rice powered by individual electrons as they tunnel through artificial atoms called quantum dots.

The tiny microwave laser --dubbed a "maser" by the scientists -- is based on a fundamental interaction between light and moving electrons, they say.

Using about a billionth of the electrical power running the average hair drier, the tiny device is the result of the researchers efforts to learn how to utilize quantum dots, bits of semiconductor material that act like single atoms, as possible components to create quantum computers.

"It is basically as small as you can go with these single-electron devices," says physics Professor Jason Petta, leader of the study published in the journal Science.

The researchers hadn't set out to build a maser; they were researching the possibility of using doubled quantum dots and joining them together to create quantum bits, or qubits, as the fundamental units of information that quantum computers will use.

"The goal was to get the double quantum dots to communicate with each other," says Yinyu Liu, a graduate student in physics working with Petta.

That communication would be by the entanglement of light photons, so the researchers created quantum dots that would emit a photon when a single electron drops from a higher energy level to a lower level to move across the double dot.

"These double quantum dots are zero-dimensional as far as the electrons are concerned -- they are trapped in all three spatial dimensions," Petta explains.

To power the process, the Princeton researchers then build their maser, which when switched on caused electrons to move one at a time in single file through each double quantum dot, causing them to emit photons.

The device, with its maser and quantum dots, constitutes a significant step forward in the effort to build quantum-computing systems using semiconductor materials, study co-author and research collaborator Jacob Taylor of the University of Maryland says.

"I consider this to be a really important result for our long-term goal, which is entanglement between quantum bits in semiconductor-based devices," he says.

"This is the first time that the team at Princeton has demonstrated that there is a connection between two double quantum dots separated by nearly a centimeter, a substantial distance," he says of the latest work.