The experimental setup for creating the laser with an artist’s impression in blue of atoms falling into a BEC and turning into a beam. Image credit: University of Amsterdam/Scixel
Lasers work through 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 is certainly possible to make a laser from matter, but practically it was difficult. Until now.
As reported in Nature, researchers at the University of Amsterdam have succeeded in producing a continuous matter laser using strontium atoms in the so-called fifth state of matter – the Bose-Einstein condensate, or BEC. To get particles into a BEC, it is necessary to cool them down to near absolute zero. Although it is very difficult to do this, you will be rewarded with something very special, the condensate behaves like a coherent wave.
The difficulties are actually due to light. Light is used to cool down atomic systems, cleverly taking away some of the energy they have by bouncing light particles — photons — onto them. But this bounce can also disrupt the BEC given the fragile nature of this state.
“In previous experiments, the gradual cooling of atoms all happened in one place. In our setup, we decided to spread the cooling steps, not in time, but in space: we let the atoms move as they go through successive cooling steps,” said team leader Florian Schreck in a statement. pronunciation†
“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 while these atoms are being used, new atoms are already on the way to complement the BEC. 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 hardships to achieve this result.
“As early as 2012, the team – then still in Innsbruck – realized a technique that allowed a BEC to be protected against laser cooling light, enabling laser cooling for the first time to the degenerate state required for coherent waves. While this was a crucial first step towards the long-held challenge of building a continuous atomic laser, it was also clear that a special machine would be needed to move forward,” explains first author Chun-Chia Chen.
“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. 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 to add an extra laser beam to solve one last technical difficulty, and immediately every photo we took showed a BEC, the first continuous wave BEC.”
The laser is continuous but the beams are not stable yet, which is the next step for this team. Once that is achieved, matter lasers can be used in a variety of applications, much like light lasers are today.