A new breakthrough has allowed physicists to create a beam of atoms that behaves similarly to a laser and can theoretically stay on “forever”.
It could finally mean that the technology is on the verge of being applied in practice, although important limitations still apply.
Nonetheless, it’s a huge step forward for what’s called an “atom laser” – a beam made up of atoms walking as a single wave that could one day be used to test fundamental physical constants. and precision engineered technology.
Atom lasers have been around for a minute. The first atom laser was created by a team of physicists at MIT in 1996. The concept seems simple enough: just as a traditional light-based laser consists of photons moving with their synchronized waves, a laser composed of atoms would require their own wave. -like nature to align before being mixed as a bundle.
As with many things in science, however, it is easier to conceptualize than to realize. At the base of the atom laser is a state of matter called the Bose-Einstein condensate, or BEC.
A BEC is created by cooling a cloud of bosons to just a fraction above absolute zero. At such low temperatures, atoms fall into their lowest possible energy state without coming to a complete stop.
When they reach these low energies, the quantum properties of the particles can no longer interfere with each other; they get close enough to each other to overlap, resulting in a high-density cloud of atoms that behaves like a “super atom” or matter wave.
However, BECs are something of a paradox. They are very fragile; even light can destroy a BEC. Since the atoms in a BEC are cooled using optical lasers, this usually means that the existence of a BEC is fleeting.
The atom lasers that scientists have achieved to date have been pulsed rather than continuous; and involve triggering a single pulse before a new BEC needs to be generated.
In order to create a continuous BEC, a team of researchers from the University of Amsterdam in the Netherlands realized that something had to change.
“In previous experiments, the gradual cooling of the atoms took place in a single place. In our setup, we decided to distribute the cooling stages not in time, but in space: we make the atoms move while ‘they progress through consecutive cooling stages.” explained physicist Florian Schreck.
“Ultimately, the 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. this way we can continue the process – essentially forever. »
This “heart of the experiment” is a trap that keeps the BEC shielded from light, a reservoir that can be continuously replenished for the duration of the experiment.
Shielding the BEC from the light produced by the cooling laser, while simple in theory, was still a bit more difficult in practice. Not only were there technical obstacles, but there were also bureaucratic and administrative obstacles.
“Moving to Amsterdam in 2013, we started with a leap of faith, borrowed funds, an empty room and a team funded entirely by personal grants,” said physicist Chun-Chia Chen, who led the research.
“Six years later, in the early hours of Christmas morning 2019, the experiment was finally about to work. We came up with the idea of adding an extra laser beam to solve one last technical difficulty, and instantly every image that we took showed a BEC, the first continuous wave BEC.”
Now that the first part of the continuous atom laser has been achieved – the “continuous atom” part – the next step, according to the team, is to work on maintaining a stable atom beam. They could achieve this by transferring the atoms to an untrapped state, thus extracting a propagating matter wave.
Because they used strontium atoms, a popular choice for BECs, the prospect opens up some interesting opportunities, they said. Atomic interferometry using strontium BECs, for example, could be used to investigate relativity and quantum mechanics, or detect gravitational waves.
“Our experiment is the matter-wave analog of a continuous-wave optical laser with fully reflective cavity mirrors,” the researchers wrote in their paper.
“This proof-of-principle demonstration provides a new, hitherto missing piece of atomic optics, enabling the construction of continuous coherent-wave devices in matter.”
The research has been published in Nature.