Physicists have been able to create a matter laser that can operate continuously.
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The experimental setup for the creation of the laser
with an artist impression in blue of atoms falling into a BEC and turning into
a beam. Image Credit: University of Amsterdam/Scixel |
Lasers work by the ability of devices to produce
coherent light waves by stimulating the emission of a particular wavelength of
electromagnetic radiation. Quantum mechanics tells us that the fundamental
truth of the universe is that waves are particles and particles are waves.
Theoretically, it's certainly possible to make a laser of matter, but
practically it has been difficult. Until now.
As reported in Nature, researchers at the University
of Amsterdam have managed to produce a continuous matter laser using atoms of
strontium in the so-called fifth state of matter – the Bose-Einstein Condensate
or BEC. To put particles in a BEC, it is necessary to cool them down to almost
absolute zero. While it is very difficult to do so, you’ll be rewarded with
something quite extraordinary, the condensate behaves like a coherent wave.
The difficulties are actually due to light. Light is
used to cool down atomic systems, by cleverly taking away some of the energy
they have by making light particles – photons – bounce off them. But this bouncing
can also disrupt the BEC given the fragile nature of this state.
“In previous experiments, the gradual cooling of atoms
was all 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 while they progress
through consecutive cooling steps," team leader Florian Schreck said in astatement.
"In the end, 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. In this way, we can keep the process going – essentially
forever.”
The first BEC was created 25 years ago and this
breakthrough was easier said than done. It took the team many years and
hardship to reach this result.
“Already in 2012, the team – then still in Innsbruck –
realized a technique that allowed a BEC to be protected from laser cooling
light, enabling for the first time laser cooling all the way down to the
degenerate state needed for coherent waves. While this was a critical first
step towards the long-held challenge of constructing a continuous atom laser,
it was also clear that a dedicated machine would be needed to take it further,”
first author Chun-Chia Chen explained.
“On moving to Amsterdam in 2013, we began with a leap
of faith, borrowed funds, an empty room, and a team entirely funded by personal
grants. Six years later, in the early hours of Christmas morning in 2019, the
experiment was finally on the verge of working. We had the idea of adding an extra
laser beam to solve a last technical difficulty, and instantly every image we
took showed a BEC, the first continuous-wave BEC.”
The laser is continuous but the beams are not stable
yet, and that’s the next step for this team. Once that's achieved, matter
lasers could be employed in a variety of applications just like light lasers
are today.
Reference: Research Paper
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