Scientists Observe First Evidence of 'Quantum Superchemistry' in The Lab

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.