A new breakthrough has allowed physicists to create a beam of atoms that behaves similarly to a laser, and which could theoretically last “forever”.
Ultimately this may mean that the technology is on its way to practical application, although important limitations still apply.
Nevertheless, it is a major step forward in what is known as an “atomic laser” – a beam made of atoms moving as a single wave that will one day be used for testing fundamental physical constants, and engineering precision technology. can be done.
Atom lasers have been around for a minute. The first atomic laser was created in 1996 by a team of MIT physicists. The concept sounds pretty simple: Just like traditional light-based lasers have photons that move in sync with their waves, a laser made of atoms would need their wave-aligned nature before shuffling them into a beam. Doing.
As is the case with many things in science, however, the concept is easier to realize. At the root of the atomic laser is a state of matter called a Bose–Einstein condensate, or BEC.
A BEC is created by cooling a boson cloud to just a fraction of absolute zero. At such a low temperature, the atoms sink to their lowest possible energy state without stopping completely.
When they reach these lower energies, the quantum properties of the particles can no longer interfere with each other; They move so close to each other that they overlap, resulting in a high-density cloud of atoms that behaves like a ‘super atom’ or matter wave.
However, BECs are something of a contradiction. They are very delicate; Light can also destroy BECs. Given that the atoms in a BEC are cooled using an optical laser, this usually means that the existence of a BEC is transitory.
The atomic lasers that scientists have managed to achieve to date are pulsed rather than continuously varied; and involves firing only one pulse before needing to generate a new BEC.
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 setup, we decided to spread the cooling phases out over time, but in space: we move the atoms while they were in successive cooling phases. progress through the medium,” explained physicist Florian Schreck.
“Finally, ultracold atoms come to the center of the experiment, where they can be used to create coherent matter waves in the BEC. But while these atoms are being used, new ones are needed to refill the BEC. The atoms are already on their way. In this way, we can continue the process – essentially forever.”
That ‘heart of the experiment’ is the mesh that shields the BEC from light, a reservoir that can be filled continuously for as long as the experiment is running.
Protecting the BEC from the light produced by the cooling laser, although simple in principle, was again slightly more difficult in practice. There were not only technical constraints, but also bureaucratic and administrative ones.
Physicist Chun-Chia Chen, who led the research, said, “When moving to Amsterdam in 2013, we started with a leap of faith, money borrowed, an empty room, and a team funded entirely by individual 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 additional laser beam to solve the last technical difficulty, and immediately every image we took was shown in a BEC, the first continuous-wave BEC.”
Now that the first part of the continuous atom laser has been realized – the “continuous atom” part – the next step, the team said, is working on maintaining a stable atomic beam. They can achieve this by moving the atoms into an untrapped state, allowing a propagating material to emit a wave.
Because they used strontium atoms, which are a popular alternative to BECs, the prospect opens up exciting opportunities, he said. For example, atomic interferometry using strontium BECs can be used to investigate relativity and quantum mechanics, or to detect gravitational waves.
“Our experiment is a matter wave analog of a continuous wave optical laser with fully reflective cavity mirrors,” the researchers write in their paper.
“This proof-of-principle demonstration provides a new, hitherto missing piece of nuclear optics, enabling the construction of continuous coherent-matter-wave devices.”
research has been published in Nature,