A new breakthrough has enabled physicists to create an atomic beam that behaves similarly to a laser, and could theoretically last “forever.”
This may finally mean that the technology is on its way to practical application, although significant limitations remain.
Nevertheless, this is a huge step forward for what is known as an “atomic laser” – a beam made of atoms that march as a single wave that could one day be used for testing fundamental physical constants and designing precision technology.
Atomic lasers have been around for a minute. The first atomic laser was created by a team at MIT physicists in 1996† The concept sounds pretty simple: Just as a traditional light-based laser is made up of photons moving in sync with their waves, a laser made of atoms would need their own wave-like nature to align before being shaken out as a beam.
A BEC is created by a cloud of bosons to 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 overlap, resulting in a cloud of high-density atoms that behaves like one “super atom,” or wave of matter.
However, BECs are something of a paradox. They are very vulnerable; even light can destroy a BEC. Since the atoms in a BEC are cooled with optical lasersthis usually means that the existence of a BEC is fleeting.
Atomic lasers that scientists have managed to achieve thus far are of the pulsed rather than continuous variety; and include firing only one pulse before a new BEC is to be generated.
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 atoms was all done in one place. In our setup, we decided not to spread the cooling steps in time, but in space: we let the atoms move as they go through successive cooling steps.” explained physicist Florian Schreck†
“Ultimately, ultracold atoms arrive at 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 the way to complement the BEC. way we can keep the process going – essentially forever.”
That ‘heart of the experiment’ is a trap that shields the BEC from light, a reservoir that can be continuously replenished as long as the experiment is running.
Protecting the BEC from the light of the cooling laser was simple in theory, but a bit more difficult in practice. There were not only technical obstacles, but 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 funded entirely by personal grants,” said physicist Chun-Chia Chenwho led the investigation.
“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 final technical problem, and immediately showed every photo we took has 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 to work on maintaining a stable atomic beam. They could achieve this by moving the atoms to an untrapped state, thus extracting a propagating wave of matter.
Because they used strontium atoms, a popular choice for BECs, the prospect presents exciting opportunities, they said. For example, atomic interferometry using strontium BECs could be used to investigate relativity and quantum mechanics, or to gravitational waves†
“Our experiment is the matter wave analog of a continuous wave optical laser with fully reflecting 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 matter wave devices.”
The research was published in Nature†
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