The world of quantum physics is mysterious. But what happens when that realm of subatomic particles is placed under immense pressure?
A team led by physicists at Washington University in St. Louis has created quantum sensors that can survive in extreme conditions.
Built inside unbreakable sheets of crystallized boron nitride, the devices can measure stress and magnetism in materials under pressure more than 30,000 times greater than the atmosphere.
“We’re the first ones to develop this sort of high-pressure sensor,” said Chong Zu, assistant professor of physics in Arts & Sciences and member of the university’s Center for Quantum Leaps.
“It could have a wide range of applications in fields ranging from quantum technology, material science, to astronomy and geology.”
Sensors built from vacancy
The work involved graduate students, postdoctoral researchers, and collaborating faculty members.
Support came in part from a US National Science Foundation training grant, which funded six months of collaborative work at Harvard University.
The team created the sensors using neutron radiation beams. These beams knocked boron atoms out of ultrathin sheets of boron nitride. The empty spots immediately trapped electrons.
Those electrons, through quantum interactions, changed their spin depending on local magnetism, stress, or temperature. Tracking the spin revealed material properties at the quantum level.
Zu’s group had earlier built similar sensors in diamonds, which power WashU’s two quantum diamond microscopes.
Diamond sensors are effective but have limitations. Because diamonds are three-dimensional, the sensors cannot easily be placed close to the material under study.
Boron nitride sheets solve this issue. They are extremely thin, less than 100 nanometers across, about 1,000 times thinner than a human hair.
“Because the sensors are in a material that’s essentially two-dimensional, there’s less than a nanometer between the sensor and the material that it’s measuring,” Zu said.
Diamonds continue to play a role. “To measure materials under high pressure, we need to put the material on a platform that won’t break,” explained graduate student Guanghui He.
The group made “diamond anvils,” small flat surfaces only 400 micrometers wide, to compress samples. “The easiest way to create high pressure is to apply great force over a small surface,” He said.
Tests confirmed the boron nitride sensors could detect subtle changes in the magnetic field of a two-dimensional magnet.
The team now plans to test other materials, including rocks from high-pressure environments like Earth’s core.
“Measuring how these rocks respond to pressure could help us better understand earthquakes and other large-scale events,” Zu said.
The sensors may also shed light on superconductivity. Known superconductors require high pressure and extremely low temperatures. Controversial claims of room-temperature superconductors remain unsettled.
“With this sort of sensor, we can collect the necessary data to end the debate,” said graduate student Ruotian “Reginald” Gong, a co-first author.
Zu said the project also highlights the importance of collaboration. “The program encourages collaboration between universities,” he said. “Now that we have these sensors, the high-pressure chamber and the diamond anvils, we’ll have more opportunities for exploration.”