Physicists engineer an atom laser that can stay on forever

The practical applications could be limitless.
Loukia Papadopoulos
The central part of the experiment in which the coherent matter waves are created.UvA

Quantum mechanics dictates that particles like atoms should also be thought of as waves and that technically we can build ‘atom lasers’ containing coherent waves of matter. The problem comes in making these matter waves last, so that they may be used in practical applications.

Now, a team of Amsterdam physicists has shown that this is indeed possible with some manipulation of the concept that underlies the atom laser, the so-called Bose-Einstein Condensate, or BEC for short, according to a press release published on June 10.

Creating a continuous Bose-Einstein Condensate

The researchers have now managed to solve the difficult problem of creating a continuous Bose-Einstein Condensate. Florian Schreck, the team leader, explained in the statement how they did it.

“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. 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," said Schrek.

While the idea was relatively simple, putting it into practice was not. Chun-Chia Chen, first author of the study recalled:

“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. 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 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.”

Now, that the researchers have been successful at creating a continuous Bose-Einstein Condensate, they hope to use the laser to create a stable output beam of matter. If they do manage to produce lasers that can not only operate forever but can also produce stable beams, the applications will be limitless.

Of course, the researchers still have some way to go. But their work is both promising and exciting.

The results of the study were published in the journal Nature.

Abstract:
Bose–Einstein condensates (BECs) are macroscopic coherent matter waves that have revolutionized quantum science and atomic physics. They are important to quantum simulation1 and sensing2,3, for example, underlying atom interferometers in space4 and ambitious tests of Einstein’s equivalence principle5,6. A long-standing constraint for quantum gas devices has been the need to execute cooling stages time-sequentially, restricting these devices to pulsed operation. Here we demonstrate continuous Bose–Einstein condensation by creating a continuous-wave (CW) condensate of strontium atoms that lasts indefinitely. The coherent matter wave is sustained by amplification through Bose-stimulated gain of atoms from a thermal bath. By steadily replenishing this bath while achieving 1,000 times higher phase-space densities than previous works7,8, we maintain the conditions for condensation. Our experiment is the matter wave analogue of a CW optical laser with fully reflective cavity mirrors. This proof-of-principle demonstration provides a new, hitherto missing piece of atom optics, enabling the construction of continuous coherent-matter-wave devices.

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