Amsterdam physicist builds atomic laser

Eternal wave of matter

Image: The central part of an experiment in which a coherent matter wave is generated. Fresh atoms (blue) fall and proceed towards the central Bose-Einstein condensation. In reality, the atom is invisible to the naked eye. Image processing with Scixel.
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Credit: UvA

It is difficult to imagine our daily life without a laser. Lasers are used in printers, CD players, pointers, measuring instruments, etc. What makes the laser special is the use of coherent waves of light. All light in the laser oscillates in perfect synchronization. Quantum mechanics, on the other hand, tells us that particles like atoms should also be considered as waves. As a result, we can build an “atomic laser” that contains waves of coherent matter. But can the waves of these substances last longer and be used in applications? In a study published this week in Nature, a team of Amsterdam physicists have shown that the answer to this question is positive.

Synchronize bosons to march

The underlying concept of the atom laser is the so-called Bose-Einstein Condensation, Or BEC for short. There are two types of elementary particles in nature, fermions and bosons. Fermions are particles like electrons and quarks, and are the building blocks of the matter we make. Bosons are very different in nature. It is not as hard as fermions, but it is soft. For example, you can move to each other without problems. The best-known example of a boson is a photon, which is the least amount of light possible. However, particles of matter can also combine to form bosons. In fact, the whole atom can behave like a particle of light. What makes bosons so special is that they are all in exactly the same state at exactly the same time, or can be expressed in more technical terms. In other words, the boson “condenses” into a coherent wave. When this kind of condensation occurs in matter particles, physicists call the resulting matter the Bose-Einstein condensation.

In everyday life, we are completely unfamiliar with these condensates. Reason: It is very difficult to operate all atoms as one. The cause of destroying synchronicity is temperature. As the material heats up, the constituent particles begin to sway, making it virtually impossible to work as one.Only at extremely low temperatures, about 1 million degrees higher than absolute zero (about 273 degrees) under (Zero on a Celsius scale), it may form a BEC coherent de Broglie wave.

Fleeting burst

A quarter of a century ago, the first Bose-Einstein Condensation was created in the Physics Lab. This opened up the possibility of building atom lasers, which are devices that literally output a beam of matter, but these devices only worked for a very short time. Lasers can generate pulses of matter waves, but after transmitting such a pulse, it was necessary to create a new BEC before transmitting the next pulse. As a first step towards Atom Laser, this wasn’t bad yet. In fact, ordinary optical lasers were created in pulse form before they could be created by physicists. continue laser. However, the development of optical lasers was very fast, the first continuous lasers were manufactured within 6 months of pulsed lasers, but for atomic lasers, continuous versions are elusive for over 25 years. I’m sorry.

It was clear what the problem was. BEC is extremely fragile and is destroyed rapidly when exposed to light. However, the presence of light is important for the formation of the condensate. To cool a substance to one millionth of a degree, the atom must be cooled using laser light. As a result, BEC was limited to momentary bursts and there was no way to maintain them consistently.

Christmas present

A team of physicists at the University of Amsterdam have succeeded in solving the difficult problem of creating a continuous Bose-Einstein condensation. Team leader Florian Schreck explains what the trick was. “In previous experiments, all the stepwise cooling of atoms was done in one place. In our setup, we decided to extend the cooling step to space rather than over time. Atoms are continuous. Move the atoms as they progress through the cooling steps. Eventually, the cryogenic atoms reach the center of the experiment, where they can be used to form coherent material waves at BEC, but these atoms are used. Meanwhile, the new atom is already on the road to replenishing BEC. In this way, the process can continue – essentially forever. ”

The underlying idea was relatively simple, but it certainly wasn’t. Chun-Chia Chen, the first author of Nature’s publication, recalls: To the degenerate state required for coherent waves. This was an important first step towards the long-standing challenge of building a continuous atomic laser, but it was also clear that a dedicated machine would be needed to take it further. When we moved to Amsterdam in 2013, we started with a team that was fully funded by a leap of faith, borrowing money, empty rooms, and personal grants. Six years later, early in the morning of Christmas 2019, the experiment was finally on the verge of functioning. The idea was to add a laser beam to solve the last technical problem, and every image taken immediately showed the first continuous wave BEC, BEC. “

Researchers who have tackled the long-standing unsolved problem of creating continuous Bose-Einstein condensation have set out to the next goal of using a laser to create a stable output beam. When lasers can not only operate forever, but also generate stable beams, they are no longer in the way of technical applications, and material lasers play an important role in technology, just like regular lasers today. May begin to play.

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