A new breakthrough has allowed physicists to create a beam of atoms that behaves in the same way as a laser and can theoretically be maintained “forever.”
This could ultimately mean that technology is on the path to practical application, although significant limitations still apply.
However, this is a big step forward for what is known as an “atom laser”: a beam of atoms that runs like a single wave that could one day be used to test fundamental physical constants and precision technology. engineering.
Atomic lasers have been around for a minute. The first atomic laser was created by a team of MIT physicists in 1996. The concept sounds pretty simple: just like a traditional light-based laser consists of photons moving with their synchronized waves, a A laser made of atoms would require its own wave — like nature — to align before being shuffled like a beam.
However, as with many things in science, it is easier to conceptualize than to realize. At the root 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, the atoms sink to their lowest possible energy state 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 cloud of high-density atoms that behaves like a “super atom” or wave of matter.
However, BECs are a kind of paradox. They are very fragile; even light can destroy a BEC. Since the atoms of a BEC are cooled by optical lasers, this usually means that the existence of a BEC is ephemeral.
The atomic lasers that scientists have managed to achieve so far have been of the pulsed variety, rather than continuous; and involve firing just one 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 needed to change.
“In previous experiments, the gradual cooling of the atoms was done all in one place. In our configuration, we decided to distribute the cooling steps not in time, but in space: we make the atoms move as they progress. for consecutive cooling steps “. explained physicist Florian Schreck.
“In the end, the ultra-cold atoms reach the heart of the experiment, where they can be used to form coherent waves of matter in a BEC. But as these atoms are used, new atoms are already on their way to replacing the BEC. “In this way, we can keep the process going, essentially forever.”
This “experiment heart” is a trap that keeps the BEC protected from light, a tank that can be filled continuously for the duration of the experiment.
Protecting the BEC from the light produced by the cooling laser, however, while simple in theory, made it a little more difficult in practice. There were not only technical but also bureaucratic and administrative hurdles.
“When we moved to Amsterdam in 2013, we started with a leap of faith, borrowed funds, an empty room, and a fully funded team with personal grants,” said physicist Chun-Chia Chen, who led the research.
“Six years later, in the early hours of Christmas morning in 2019, the experiment was finally about to work. We had the idea of adding an additional laser beam to solve one last technical difficulty, and instantly every image that we did showed a BEC., the first BEC of continuous wave “.
Now that the first part of the continuous atom laser has been made, the “continuous atom” part, the next step, the team said, is working to maintain a stable beam of atoms. They could do this by transferring atoms to an untouched state, thus extracting a wave of propagating matter.
Because they used strontium atoms, a popular choice for BECs, the prospect opens up exciting opportunities, they said. Atomic interferometry with strontium BEC, for example, could be used to conduct research on relativity and quantum mechanics, or to detect gravitational waves.
“Our experiment is the subject-matter 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 piece of atomic optics that was hitherto lacking, which allows the construction of continuous wave devices of coherent matter.”
The research has been published in Nature.