Physicists Uncover Quantum Structure of Buckminsterfullerene

A team of physicists from the Joint Institute for Lab Astrophysics (JILA) and IMRA America Inc. has measured hundreds of individual quantum energy levels in buckminsterfullerene (nicknamed buckyball), a 60-atom molecule of carbon in the shape of a soccer ball.

Changala et al used frequency combs, or ‘rulers of light,’ to observe individual quantum energy transitions in buckminsterfullerene. Image credit: Steven Burrows / JILA.

Changala et al used frequency combs, or ‘rulers of light,’ to observe individual quantum energy transitions in buckminsterfullerene. Image credit: Steven Burrows / JILA.

Buckminsterfullerene (C60) is extremely complex. Due to its enormous 60-atom size, the overall molecule has a staggeringly high number of ways to vibrate — from 1026 to 1030 vibrational quantum states when the molecule is warm.

“Buckyballs, first discovered in 1984, have created great scientific excitement,” said NIST/JILA fellow Dr. Jun Ye.

“But high-resolution spectroscopy, which can reveal the details of the molecule’s rotational and vibrational properties, didn’t work at ordinary room temperatures because the signals were too congested.”

Dr. Ye and co-authors used an updated version of their frequency comb spectroscopy and cryogenic buffer gas cooling system to observe isolated, individual energy transitions among rotational and vibrational states in cold, gaseous buckminsterfullerene.

Low temperatures (about minus 138 degrees Celsius, which is minus 216 degrees Fahrenheit) enabled the researchers to concentrate the molecules into a single rotational-vibrational quantum state at the lowest energy level and probe them with high-resolution spectroscopy.

“Buckminsterfullerene is the most symmetric molecule known, with a soccer-ball-like shape known as a modified icosahedron,” they said.

“It is small enough to be fully understood with basic quantum mechanics principles. Yet it is large enough to reveal insights into the extreme quantum complexity that emerges in huge systems.”

“As an example of practical applications, buckyballs could act as a pristine network of 60 atoms.”

The core of each atom possesses an identical property known as ‘nuclear spin,’ which enables it to interact magnetically with its environment. Therefore, each spin could act as a magnetically controlled quantum bit or ‘qubit’ in a quantum computer.

“If we had a buckyball made of pure isotopic carbon-13, each atom would have a nuclear spin of 1/2, and each buckyball could serve as a 60-qubit quantum computer. Of course, we don’t have such capabilities yet; we would need to first capture these buckyballs in traps,” Dr. Ye said.

A key part of the new quantum revolution, a quantum computer using qubits made of atoms or other materials could potentially solve important problems that are intractable using today’s machines.

“There are also a lot of astrophysics connections. There are abundant buckyball signals coming from remote carbon stars, so the new data will enable scientists to better understand the Universe,” Dr. Ye said.

After they measured the quantum energy levels, the physicists collected statistics on nuclear spin values of buckminsterfullerene.

They confirmed that all 60 atoms were indistinguishable, or virtually identical.

Precise measurements of the buckminsterfullerene’s transition energies between individual quantum states revealed its atoms interacted strongly with one another, providing insights into the complexities of its molecular structure and the forces between atoms.

The results appear in the journal Science.

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P. Bryan Changala et al. 2019. Rovibrational quantum state resolution of the C60 fullerene. Science 363 (6422): 49-54; doi: 10.1126/science.aav2616

 

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