Scientists at the Houston’s Rice University, Texas have seen lithium atoms passing through other particles of matter in ultra-cold conditions. Bose Einstein condensates (BECs) are a state of matter that form at temperatures near absolute zero. Atoms and sub atomic particles at this temperature have been seen to merge into one quantum mechanical unit – a “matter wave” of energy. This newly discovered property is being compared to a magician’s disappearing act.

“The team carrying on these experiments chilled a huge number of lithium atoms to one-millionth of a degree of absolute zero, creating a BEC state called a soliton. In a soliton formation, the atoms experienced balanced quantum pressure that exhibited attractive forces while being pushed apart. This quality enabled them to pass through each other without ever being in the same spot.”

“It happens because of ‘wave packet’ interference. Think of them as waves that can have a positive or negative amplitude. One of the solitons is positive and the other is negative, so they cancel one another. The probability of them being in the spot where they meet is zero. They pass through that spot, but you never see them there,” said physicist and team leader Randy Hulet.

Hulet’s team specializes in experiments on BECs and other matter under extremely frigid conditions. They use lasers to both trap and cool clouds of lithium gas to temperatures that are so cold that the matter’s behavior is dictated by fundamental forces of nature that aren’t observable at higher temperatures.

Hulet and postdoctoral research associate Jason Nguyen, the lead author of the study, balanced the forces of attraction and repulsion in BECs to create solitons.

“First we make a Bose Einstein condensate and then we use a sheet of light to split the condensate in half and push the two halves apart,” Nguyen said. “We hold them apart and turn each of them into solitons, and then we take the sheet away and let them fall back toward one another and collide.”

Images of the extremely small BECs were taken during the experiments, wherein they were seen “oscillating back and forth like pendulums swinging in opposite directions.”

The research team carried out many experiments and came across different findings. While some solitons were seen to pass through each other, others simply bounced off others. The difference in behavior could be attributed to solitons’ phase of the waves, a factor that cannot be controlled. “In the out-of-phase case, the one with the gap, where it appeared that they had been bouncing off of each other, we still saw the gap but we also saw the larger soliton emerge unfazed on the other side of the gap. In other words, it jumped through the gap,” said Hulet. The study was published in the journal Nature Physics.

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