In new state of matter, echoes of a medieval symbol
and World Science staff
An international team of physicists has converted three atoms into a new state of matter whose existence a Russian scientist predicted in 1970.
In this state, any two of the atoms repel each other when close together, “but when you put three of them together, it turns out that they attract and form a new state,” said the University of Chicago’s Cheng Chin.
It’s called an “Efimov state,” after the Russian, Vitaly Efimov.
Chin and 10 other scientists described the finding in the March 16 issue of the research journal Nature. In the laboratory of Rudolf Grimm at the University of Innsbruck in Austria, they reported, they observed the Efimov state in a vacuum chamber at a frigid minus 459.6 degrees Fahrenheit. That’s equivalent to a billionth of a degree above “absolute zero,” the coldest temperature that can exist.
The new state behaves like a Borromean ring, a symbol of three interlocking circles that has historical significance in Italy, the researchers explained. The Borromean concept also exists in physics, chemistry and mathematics.
“This ring means that three objects are entangled. If you pick up any one of them, the other two will follow. However, if you cut one of them off, the other two will fall apart,” Chin said. “There is something magic about this number of three.”
The physicists said they coaxed three atoms of cesium, a soft metal used in atomic clocks, into the Efimov state. But in theory the state is possible for any sets of three particles at ultracold temperatures, according to Chin. “If you can create this kind of state out of any other type of particle, it’ll have exactly the same behavior,” he said.
“After working on cesium for many years, this is a dream come true for me,” he added.
The finding may spur new research programs devoted to understanding the quantum mechanical behavior of just a few interacting particles, Grimm said.
Quantum mechanics, the study of physical laws governing the smallest things, is well worked out when it comes to explaining the interactions of either two particles, or many, Chin said. But a good understanding of systems containing a handful of particles is elusive. That may change as scientists start to produce experiments that simulate systems of three or four particles, like those found in atomic nuclei.
Now that the Efimov state has been achieved, scientists can aspire to engineer the properties of matter, Chin said.
Today, scientists can combine atoms in different ways to form materials with interesting new properties, “but you are not changing the fundamental interactions of these atoms,” Chin said. The new findings, he added, expand those horizons. He said the researchers exerted total control over the atoms in the experiments, converting them into the Efimov state and back at will.
“This so-called quantum control over the fundamental properties of matter now seems feasible. We’re not limited to the properties of, say, aluminum, or the properties of the copper of these particles. We are really creating a new state in which we can control their properties.” But not too easily: for now, he added, it seems this can only be done at temperatures near absolute zero.
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