Lasers work by the ability of devices to produce coherent light waves by stimulating the emission of a particular wavelength of electromagnetic radiation. Quantum mechanics tells us that the fundamental truth of the universe is that waves are particles and particles are waves. Theoretically, it's certainly possible to make a laser of matter, but practically it has been difficult. Until now.

As reported in Nature, researchers at the University of Amsterdam have managed to produce a continuous matter laser using atoms of strontium in the so-called fifth state of matter – the Bose-Einstein Condensate or BEC. To put particles in a BEC, it is necessary to cool them down to almost absolute zero. While it is very difficult to do so, you’ll be rewarded with something quite extraordinary, the condensate behaves like a coherent wave.

The difficulties are actually due to light. Light is used to cool down atomic systems, by cleverly taking away some of the energy they have by making light particles – photons – bounce off them. But this bouncing can also disrupt the BEC given the fragile nature of this state.

“In previous experiments, the gradual cooling of atoms was all done in one place. In our setup, we decided to spread the cooling steps, not over time, but in space: we make the atoms move while they progress through consecutive cooling steps," team leader Florian Schreck said in a statement.  

"In the end, ultracold atoms arrive at the heart of the experiment, where they can be used to form coherent matter waves in a BEC. But while these atoms are being used, new atoms are already on their way to replenish the BEC. In this way, we can keep the process going – essentially forever.”

The first BEC was created 25 years ago and this breakthrough was easier said than done. It took the team many years and hardship to reach this result.

“Already in 2012, the team – then still in Innsbruck – realized a technique that allowed a BEC to be protected from laser cooling light, enabling for the first time laser cooling all the way down to the degenerate state needed for coherent waves. While this was a critical first step towards the long-held challenge of constructing a continuous atom laser, it was also clear that a dedicated machine would be needed to take it further,” first author Chun-Chia Chen explained.

“On moving to Amsterdam in 2013, we began with a leap of faith, borrowed funds, an empty room, and a team entirely funded by personal grants. Six years later, in the early hours of Christmas morning in 2019, the experiment was finally on the verge of working. We had the idea of adding an extra laser beam to solve a last technical difficulty, and instantly every image we took showed a BEC, the first continuous-wave BEC.”

The laser is continuous but the beams are not stable yet, and that’s the next step for this team. Once that's achieved, matter lasers could be employed in a variety of applications just like light lasers are today.