Physicists Uncover Quantum Structure of Buckyballs
By: LAURA OST, NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY JANUARY 30, 2019
JILA researchers used frequency combs, or “rulers of light,” to observe individual quantum energy transitions in buckyballs. Credit: Steven Burrows/JILA
JILA researchers have measured hundreds of individual quantum energy levels in the buckyball, a spherical cage of 60 carbon atoms. It’s the largest molecule that has ever been analyzed at this level of experimental detail in the history of quantum mechanics. Fully understanding and controlling this molecule’s quantum details could lead to new scientific fields and applications, such as an entire quantum computer contained in a single buckyball.
The buckyball, formally known as buckminsterfullerene, is extremely complex. Due to its enormous 60-atom size, the overall molecule has a staggeringly high number of ways to vibrate—at least 100,000,000,000,000,000,000,000,000 vibrational quantum states when the molecule is warm. That’s in addition to the many different energy states for the buckyball’s rotation and other properties.
As described in the January 4 issue of Science, the JILA team 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 buckyballs. This is the first time anyone has been able to prepare buckyballs in this form to analyze its rotations and vibrations at the quantum level.
JILA is jointly operated by the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder.
Buckyballs, first discovered in 1984, have created great scientific excitement. 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, NIST/JILA Fellow Jun Ye said. Low temperatures (about -138 degrees Celsius, which is -216 degrees Fahrenheit) enabled researchers to concentrate the molecules into a single rotational-vibrational quantum state at the lowest energy level and probe them with high-resolution spectroscopy.
The buckyball is the most symmetric molecule known, with a soccer-ball-like shape known as a modified icosahedron. 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.