A New Form of Matter 2 - Fermionic Condensates

Now we have fermionic condensates--so new that most of their basic properties are unknown. Certainly they're cold. Jin created the substance by cooling a cloud of 500,000 potassium-40 atoms to less than a millionth of a degree above absolute zero. And they probably flow without viscosity. Beyond that...? Researchers are still learning.

"When you find a new form of matter," notes Jin, "it takes a while to understand it."

Fermionic condensates are related to BECs. Both are made of atoms that coalesce at low temperatures to form a single object. In a BEC, the atoms are bosons. In a fermionic condensate the atoms are fermions.

What's the difference?

Bosons are sociable; they like to get together. As a rule of thumb, any atom with an even number of electrons + protons + neutrons is a boson. So, e.g., ordinary sodium atoms are bosons, and they can merge to become Bose-Einstein condensates.

Fermions, on the other hand, are antisocial. They are forbidden (by the "Pauli Exclusion Principle" of quantum mechanics) to gather together in the same quantum state. Any atom with an odd number of electrons + protons + neutrons, like potassium-40, is a fermion.

more Bosons are social; fermions are antisocial.

Jin's group found a way around the antisocial behaviour of fermions. They used a carefully applied magnetic field to act like a fine-tunable "Cupid." The field causes loner atoms to pair up, and the strength of that pairing can be controlled by adjusting the magnetic field. Weakly paired potassium atoms retain some of their fermionic character, but they also behave a bit like bosons. A pair of fermions can merge with another pair--and another and another--eventually forming a fermionic condensate.

Jin suspects that the subtle pairing of atoms in a fermionic condensate is the same pairing phenomenon seen in liquefied helium-3, a superfluid. Superfluids flow without viscosity, so fermionic condensates should do the same.

A closely related phenomenon is superconductivity. In a superconductor, paired electrons (electrons are fermions) can flow with zero resistance. There is intense commercial interest in superconductors because they could be used to produce cheaper, cleaner electricity, and to build high-tech marvels like levitating trains and ultra-fast computers. Unfortunately, superconductors are difficult to handle and study.