Frozen cloud of molecules acts as a single quantum object

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An image of caesium molecules in a Bose-Einstein condensate

Chin Lab

For the first time, researchers have created a frozen cloud of molecules that share the same quantum state, meaning it behaves as if it were a single molecule. The arrangement provides a blank slate for experiments that could yield new materials, such as room-temperature superconductors.

Cheng Chin at the University of Chicago and his colleagues formed a Bose-Einstein condensate (BEC) from thousands of caesium molecules, using lasers to remove their energy and cool them to near absolute zero.

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BECs are often called the fifth state of matter, after solids, liquids, gases and plasmas, and their particles share the same quantum properties as each other. Chin says this is the ideal initial condition for any experiment, as it removes many variables. “They all work together, they all work in the same way. What they are going to do next, they’ll be doing that together. Essentially, it’s a kind of giant molecule,” he says.

Scientists have been creating BECs with atoms since the 1990s, but cooling molecules to this extreme quantum state has proved more difficult. “Eventually you run out of ideas how to get colder,” says Chin.

Instead, the team took a different approach, starting with a single layer of atoms in a BEC and using a magnetic field to induce pairs of atoms to form molecules while still in the BEC state. These molecules remained stable at just 10 nanokelvin – fractionally above absolute zero. The team used a wide and very thin laser beam to hold the molecules in place as two-dimensional atomic sheets.

Peter Krüger at the University of Sussex, UK, says: “They’ve taken something that’s been around for maybe 25 years with atoms to the next level. The level of complexity is so much greater.”

He believes the breakthrough will open the door to new research that could ultimately lead to the discovery of materials with interesting properties, such as room-temperature superconductors. Superconducting materials have no electrical resistance, but have so far only worked at extremely low temperatures.

“It’s truly a big step. But no one should think that this is technology that would be found in some practical device any time soon,” he says. “It’s a great tool to understand a new level of quantum physics by enabling new studies, not to build new devices that will help you or I in our everyday lives.”

Journal reference: Nature, DOI: 10.1038/s41586-021-03443-0

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