Strange things happen at the quantum level. Whole clouds of particles may
get entangled, losing their uniqueness as they work together.
For the first time, scientists have witnessed ultracold atoms chilled to
a quantum state chemically behaving as a group, rather than arbitrarily
generating new molecules after accidentally colliding.
"What we saw lined up with the theoretical predictions,"
says
Cheng Chin, a physicist at the University of Chicago and the study's
senior author. "This has been a scientific goal for the past 20 years, so
it's a very exciting era."
Heat energy causes all particles, atoms, and molecules to vibrate within
the constraints of their atomic structure or jostle alongside other
molecules in a material. Particles are coaxed into a less chaotic state by
cooling them to ultracold temperatures;
putting them in an optical trap
also limits their mobility.
Scientists demonstrated
decades ago
that when temperatures approached absolute zero, particles began to mesh
together into conglomerates with a shared quantum identity, their separate
qualities being wiped out by bizarre collective behaviors that came to
dominate.
Molecules, on the other hand, are significantly more difficult to control
than atoms. However, by 2019, scientists had
discovered
a means to
coax them
into shared quantum states as well.
Scientists hypothesized that if molecules cohere or
stick together
when coaxed into the same quantum state, a completely new type of
chemistry may emerge inside the quantum landscape.
This shared quantum state, known as quantum degeneracy, was seen in some
situations to
inhibit chemical processes
at a pace
substantially larger
than cold temperatures normally slow chemical reactions.
Researchers also suspected that if molecules sharing a quantum state were
'coupled' together and reacted as one, they may induce faster chemical
processes. However, like with any experiment investigating the quantum
world, seeing this hypothesized phenomenon has proven challenging.
"Observation of these many-body phenomena, also known as'superchemistry,'
has been elusive thus far,"
write Chin and colleagues in their article.
Chin and colleagues attempted this by trapping an ultracold gas of
cesium
atoms in an optical trap and binding them in a common quantum state. The
researchers then used a magnetic field to create a chemical reaction that
converted them into molecules, and they studied the process
kinetics.
Their findings indicate that chemical processes in a degenerate quantum
gas differ from those in a normal gas.
The scientists discovered a sharp decrease in particle collisions below a
certain temperature. Meanwhile, when atoms disappeared in the chemical
process, scientists saw a rapid creation of molecules - the particles had
entered a quantum degenerate domain, and reactions were occurring quicker
than they would under normal conditions.
"The sharp transition of the molecule formation rate around the critical
temperature Tc indicates different laws in the classical and quantum
degenerate regimes,"
write
Chin and colleagues.
After the magnetic field was removed, the surviving atoms and molecules
oscillated in a coherent coupling for several milliseconds. Further
investigation uncovered the underlying reaction mechanism, which the
researchers
characterize
as proof of a 'quantum-enhanced' chemical process.
However, because the studies included the formation of small, two-atom
molecules, the team's results will need to be replicated before we can be
certain of what we're seeing. Experimentation with bigger, more
complicated compounds is also planned.
"The observation of coherent and collective chemical reactions in the
quantum degenerate regime opens the door to further investigation of the
interaction between many-body physics and ultracold chemistry," the
researchers
conclude.
The study has been published in
Nature Physics.
