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Until now, atoms have never been imaged interacting freely in space, but a new technique known as non-resolved microscopy has changed that.
MIT physicists were able to successfully capture images of interacting bosons and fermions that were frozen in place and then illuminated. The images proved previous predictions about these types of atoms.
This demonstrates that there is real, tangible proof of mathematical predictions in the physical world.
What do atoms do when we’re not watching? It turns out they do exactly what we thought.
Enigmatic because of their quantum nature—meaning that they behave as both particles and waves—atoms had never been visualized freely interacting with each other. Where an atom is and how fast it is moving through space cannot be determined simultaneously. Before, it had been possible to make out the shape and structure of entire clouds of atoms using probes, but the individual atoms within the cloud eluded observation. Now, a team of researchers from MIT have finally managed to capture their interactions for the first time.
Led by physicist Martin Zwierlein, the team developed a technique that allowed them to freeze atoms in place and put them in the spotlight with lasers. They were able to successfully image bosons of a sodium isotope and fermions of a lithium isotope before these atoms scattered again. (Bosons—like the infamous Higgs Boson—have spins of integer values, while fermions—like electrons, protons, and neutrons—have odd half-integer spins.) Both isotopes were in the form of quantum gases.
Bosons were previously predicted to bunch together in a wave form, exhibiting the wave part of quantum behavior, while fermions were predicted to repel those like them and form pairs with different fermions, which illustrates particle behavior. The probability of finding bosons near each other is high, while there is a low chance of seeing fermions as close together, and the gases needed to be at ultracold temperatures to see anything at all (because atoms get the zoomies when agitated by heat).
“Imaging quantum gases in situ at the resolution of single atoms realizes the ultimate depth of information one may obtain in real space,” Zwierlein and his team said in a study recently published in Physical Review Letters.
Their new technique, known as non-resolved microscopy, involves using a laser beam to trap the atoms in one place. There, they are free to interact before they are exposed to a lattice of light that freezes them in place. The atoms are then illuminated with fluorescent light to expose where they are and what they are doing. There was some difficulty in lighting these atoms up, since too much heat would send them flying all over. As a result, this is the first time Zwierlein managed to freeze the motion of strongly interacting atoms in situ, and he was able to capture images of both bosons and fermions.
With bosons, the team formed a Bose-Einstein condensate, which is a boson gas cloud cooled to temperatures verging on absolute zero. The MIT team wanted to prove the existing prediction that bosons bunch together because of their high probability of being near each other and their ability to share the same quantum mechanical wave. Atoms in this type of wave show wave-like behavior as they keep changing in time and space, but the properties of those atoms are difficult to observe. The image of bosons shows atoms bunching together with wavelike trails of light behind them, indicating that they are moving in waves.
To image a fermion cloud, the team needed two types of fermions—they wanted to capture pairs, and fermions of only one type would end up repelling each other. Sure enough, fermions of the same type avoided each other, while opposite fermions attracted each other.
Zwierlein plans to continue using non-resolved microscopy to understand more about the physical world and potentially image stranger, more exotic quantum phenomena.
“This kind of pairing is the basis of a mathematical construction people came up with to explain experiments. But when you see pictures like these, it’s showing in a photograph, an object that was discovered in the mathematical world,” Richard Fletcher, a coauthor of the study and physicist from MIT, said in a recent press release. “So it’s a very nice reminder that physics is about physical things. It’s real.”
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