The Bose-Einstein condensate (BEC) is considered the fifth state of matter after plasma, solid, liquid, and gas. It is a peculiar state where quantum mechanical phenomena, which are usually microscopic, become macroscopic. This state has been successfully created on the International Space Station (ISS) and researchers have now published the first results from the project in the journal Nature.
The achievement was possible thanks to the Cold Atom Laboratory (CAL), an experiment launched to the space station in May 2018. The CAL is literally the coldest place in space that we know of. With a temperature just a fraction of a degree above absolute zero, the lab is perfectly designed to create the Bose-Einstein condensate and make these states long-lived.
The space station is in constant free-fall, moving around the Earth at an incredible 7.66 kilometers (4.76 miles) per second. The motion creates an environment where the pesky action of gravity doesn’t affect people or experiments. This is a crucial reason why studying the Bose-Einstein condensate on the ISS is so important.
Bose-Einstein condensates are created in confined traps. To study the state, these traps are switched off so that researchers can follow how the Bose-Einstein condensate changes. During this time, the Bose-Einstein condensate is said to be in free-expansion, which is one of the advantages of doing this experiment in microgravity. There, the free-expansion time is much longer. On Earth, the experiments last for tens of milliseconds due to gravity. Inside the Cold Atom Laboratory, the free-expansion went beyond one second, which allows for higher precision in the measurements.
The reduced gravity also allows for lower temperatures. The traps down on Earth have stronger forces to keep the state stable. In space, they are much weaker, adding little energy to the system and allowing researchers to probe even more exotic quantum phenomena.
“We have used the baseline capabilities of CAL in low Earth orbit to demonstrate immediate and fundamental benefits of microgravity for ultracold atom experiments, including demonstration of novel evaporation regimes and by-products, free-space BEC expansion times over one second in duration, and decompression-cooled condensates with picokelvin effective temperatures,” the authors wrote in the paper.
“These experiments form the start of potentially years of science operations, with additional capabilities of the instrument to be employed over time.”
Since long-lived Bose-Einstein condensate states could used in a series of remote sensing technologies on satellites, there's interest in how their properties change in space.