Quantum Researchers Broke 60-Year-Old Laser Limit, Says Study

A team of researchers found a flaw in a 1958 paper on lasers, heralding the coming of a super-laser.
Brad Bergan
The photo credit line may appear like thisWrongTog / Unsplash

A team of quantum theorists in Australia has demonstrated how to break a bound believed for 60 years to be a fundamental limit to the coherence of lasers, according to a recent paper published in the journal Nature Physics.

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Quantum researchers break 60-year-old laser limit

Laser beam coherence involves the number of photons — also described as light particles — emitted consecutively into the beam with the same phases — in other words, while all waving together. This affects the laser's ability to carry out several precision tasks, like controlling all components of a quantum computer, according to Phys.org.

In the recent paper, the researchers from Griffith University and Macquarie University uncovered a means to make this coherence substantially larger than earlier thought, thanks to quantum technology.

"The conventional wisdom dates back to a famous 1958 paper by American physicists Arthur Schawlow and Charles Townes," said Project Leader and Director of Griffith's center for quantum dynamics, Professor Wiseman.

Assumptions from 1958 laser experiment were wrong

All of the physicists behind the 1958 paper later won a Nobel prize for their work with lasers.

"They showed theoretically that the coherence of the beam cannot be greater than the square of the photons stored in the laser," added Wiseman. "But they made assumptions about how the energy is added to the laser and how it is released to form the beam."

When the initial experiments were performed, the assumptions made sense, explained Wiseman. While they are still applied to most lasers today, they aren't needed within the study of quantum mechanics.

New quantum model achieves upper laser limit

"In our paper, we have shown that the true limit imposed by quantum mechanics is that the coherence cannot be greater than the fourth power of the number of photons stored in the laser," said Dominic Berry, an associate professor from Macquarie University.

"When the stored number of photons is large, as is typically the case, our new upper bound is much bigger than the old one," he added. And the new bound is achievable, said researcher Nariman Saadatmand, who works in Wiseman's group.

"By numerical simulation we have found a quantum mechanical model for a laser which achieves the theoretical upper bound for coherence, in a beam that is otherwise indistinguishable from that of a conventional laser," said Saadatmand.

Super-lasers still a long way from common sight

However, we probably won't get to see the new super-lasers for a long time, according to Travis Baker — a doctoral student working on the project at Griffith University. "But we do prove that it would be possible to construct our truly quantum-limited laser using superconducting technology. This is the same technology used in current best quantum computers, and our proposed device may have applications in that field."

Quantum mechanics is a very paradoxical field, capable of constantly transforming the way we view not only universe, but also technology. While no one would turn down a super-laser off the shelf, it seems we have a long time to wait until it becomes a reality.

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