A new breakthrough has made it possible for physicists to create a ray of atoms that behaves in the same way as a laser, and which could theoretically remain “forever”.
This may finally mean that the technology is on its way to practical application, although significant limitations still apply.
Still, this is a big step forward for what is called an “atomic laser” – a beam made of atoms that marches as a single wave that could one day be used to test basic physical constants and technical precision techniques.
Atomic lasers have been around for a minute. The first nuclear laser was created by a team from MIT physicist as early as 1996. The concept sounds pretty simple: just as a traditional light-based laser consists of photons moving with its waves in sync, a laser made of atoms would require its own wave-like nature to adapt before it is mixed out like a beam.
A BEC is created by cooling a cloud bosoner to just a fraction above absolute zero. At such low temperatures, the atoms sink to their lowest possible state of energy without stopping completely.
When they reach these low energies, the quantum properties of the particles can no longer interfere with each other; they move close enough to each other to overlap, resulting in a high-density cloud of atoms behaving like a “superatom” or a wave of matter.
However, BEC is something of a paradox. They are very fragile; even light can destroy a BEC. Given that the atoms in a BEC are cooled with optical lasersthis usually means that a BEC’s existence is fleeting.
Atomic lasers that scientists have succeeded in achieving so far have been of pulsating rather than continuous kind; and means only firing a pulse before a new BEC needs to be generated.
To create a continuous BEC, a team of researchers at the University of Amsterdam in the Netherlands realized that something needed to change.
“In previous experiments, the gradual cooling of atoms was 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 as they go through successive cooling steps.” explained physicist Florian Schreck.
“Ultimately, ultra-cold atoms come to the core 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 filling BEC. In this way we can keep the process going – in principle forever. “
That “heart of the experiment” is a trap that keeps the BEC protected from light, a reservoir that can be continuously replenished as long as the experiment lasts.
Protecting BEC from the light produced by the cooling laser was, however, although in theory simple, again a little more difficult in practice. There were not only technical barriers, but there were also bureaucratic and administrative ones.
“When we moved to Amsterdam in 2013, we started with a leap of faith, borrowed money, an empty room and a team fully funded by personal grants.” said physicist Chun-Chia Chenwho led the research.
“Six years later, early on Christmas morning 2019, the experiment was finally about to work. We had the idea to add an extra laser beam to solve one last technical difficulty, and immediately each image we took showed a BEC, the first continuous wave BEC . “
Now that the first part of the continuous atomic laser has been realized – the “continuous atom” part – the next step, the team said, is working to maintain a stable atomic beam. They could achieve this by transferring the atoms to a free state, thereby extracting a propagation wave.
Because they used strontium atoms, a popular choice for BEC, the prospects open up exciting opportunities, they said. Atomic interferometry using strontium BEC, for example, could be used to conduct relativity and quantum mechanics studies, or to detect gravitational waves.
“Our experiment is the matter-wave analog of a continuous-wave optical laser with fully reflecting cavity mirrors,” wrote the researchers in their essay.
“This proof-of-principle demonstration provides a new, hitherto missing piece of atomic optics, enabling the construction of continuous coherent matter waves.”
The research has been published in Nature.
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