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Researchers Make Coldest Quantum Gas of Molecules (phys.org)
An anonymous reader quotes a report from Phys.Org: JILA researchers have made a long-lived, record-cold gas of molecules that follow the wave patterns of quantum mechanics instead of the strictly particle nature of ordinary classical physics. The creation of this gas boosts the odds for advances in fields such as designer chemistry and quantum computing. As featured on the cover of the Feb. 22 issue of Science, the team produced a gas of potassium-rubidium (KRb) molecules at temperatures as low as 50 nanokelvin (nK). That's 50 billionths of a Kelvin, or just a smidge above absolute zero, the lowest theoretically possible temperature. The molecules are in the lowest-possible energy states, making up what is known as a degenerate Fermi gas.
In a quantum gas, all of the molecules' properties are restricted to specific values, or quantized, like rungs on a ladder or notes on a musical scale. Chilling the gas to the lowest temperatures gives researchers maximum control over the molecules. The two atoms involved are in different classes: Potassium is a fermion (with an odd number of subatomic components called protons and neutrons) and rubidium is a boson (with an even number of subatomic components). The resulting molecules have a Fermi character. Before now, the coldest two-atom molecules were produced in maximum numbers of tens of thousands and at temperatures no lower than a few hundred nanoKelvin. JILA's latest gas temperature record is much lower than (about one-third of) the level where quantum effects start to take over from classical effects, and the molecules last for a few seconds -- remarkable longevity. These new ultra-low temperatures will enable researchers to compare chemical reactions in quantum versus classical environments and study how electric fields affect the polar interactions, since these newly created molecules have a positive electric charge at the rubidium atom and a negative charge at the potassium atom. Some practical benefits could include new chemical processes, new methods for quantum computing using charged molecules as quantum bits, and new precision measurement tools such as molecular clocks.
In a quantum gas, all of the molecules' properties are restricted to specific values, or quantized, like rungs on a ladder or notes on a musical scale. Chilling the gas to the lowest temperatures gives researchers maximum control over the molecules. The two atoms involved are in different classes: Potassium is a fermion (with an odd number of subatomic components called protons and neutrons) and rubidium is a boson (with an even number of subatomic components). The resulting molecules have a Fermi character. Before now, the coldest two-atom molecules were produced in maximum numbers of tens of thousands and at temperatures no lower than a few hundred nanoKelvin. JILA's latest gas temperature record is much lower than (about one-third of) the level where quantum effects start to take over from classical effects, and the molecules last for a few seconds -- remarkable longevity. These new ultra-low temperatures will enable researchers to compare chemical reactions in quantum versus classical environments and study how electric fields affect the polar interactions, since these newly created molecules have a positive electric charge at the rubidium atom and a negative charge at the potassium atom. Some practical benefits could include new chemical processes, new methods for quantum computing using charged molecules as quantum bits, and new precision measurement tools such as molecular clocks.
This is actually accurate. All "subatomic components" (protons, neutrons, and electrons) are fermions. Put an odd number of fermions together, and you get a composite fermion. Put an even number of fermions together, and you create a composite boson. So whether the atom is a fermion or boson can be established by counting the subatomic building blocks in the atom. Since atoms have one electron per proton if they're not ionized, you can alternatively say that an odd vs. even number of neutrons decides whether the atom is a fermion or boson (so e.g. He-3 is a fermion, while He-4 is a boson).
This is important to cold atomic gases because the Pauli exclusion principle only applies to fermions. This means that fermions usually repel each other, while boson gases do this.
Actually, rubidium is a boson, the article is correct. Fundamentally, the distinction between bosons and fermions is the distinction between particles that follow Bose-Einstein statistics (bosons) and those that follow Fermi-Dirac statistics (fermions). Due to the spin-statistics theorem, you end up with bosons having integral spins (0, 1, etc.) and fermions having half-integral spins (1/2, 3/2, etc.). The short version of the statistics is that fermions obey the Pauli exclusion principle (so they repel each other), while bosons do not (so they can condense into a macroscopic quantum state).
It so happens that for the elementary particles in the standard model, all matter particles (leptons and quarks) are fermions, while what we call force carriers (photons etc.) are bosons. But this does not hold true in general. For composite particles, you end up with an odd number of subatomic particles combining to form a fermion, while an even number of subatomic particles form a boson. This is again relevant because e.g. He-3 is a composite fermion, so a cold gas of those atoms will repel each other due to the Pauli exclusion principle; while He-4 is a composite boson, so a cold gas of those atoms will form a macroscopic quantum state known as a "Bose-Einstein condensate". Thus, just changing the number of neutrons in the nucleus actually has an enormous effect on the behavior of a gas at sufficiently low temperatures. (In the case of He-3 and He-4, the latter can form a superfluid directly, while the former has to create boson-like pairs in a manner that is similar to what happens in superconductors before any exotic phase transition can take place.)
Actually, referring to fermions as "matter particles" and bosons as "force carriers" is an oversimplification, and is only true for the elementary particles of the standard model. The true distinction between them is that fermions follow Fermi-Dirac statistics, while bosons follow Bose-Einstein statistics. In practice, this means that fermions follow the Pauli exclusion principle (and thus repel each other), while bosons do not (and can condense into macroscopic quantum states).
If you put together these elementary particles, it turns out that an odd number of them forms a composite fermion, while an even number of them forms a composite boson. If you want to think about it in terms of the spin-statistics theorem you referred to: you can put together two spin-1/2 fermions to form either a spin-0 or a spin-1 composite particle, and either one would be a boson. But if you put together three spin-1/2 fermions, the result has to be a spin-1/2 or spin-3/2 particle, which is again a fermion.
This is very important at low temperatures, since e.g. He-3 atoms (fermions) repel each other, while He-4 atoms (bosons) do not, so only the latter can directly enter a macroscopic quantum state. The same distinction is relevant for the common isotopes of potassium and rubidium.
So in this case, the error in science journalism is not calling potassium a fermion and rubidium a boson. The error is to call fermions "matter particles" and bosons "force carriers". That is a simplification that only happens to be true for the elementary particles, but not composite particles.