Looking into ‘problems in the matrix’: the team finds ways to harness the quantum power of atomic defects

The most interesting parts of nature are often the imperfections. This is especially true in quantum physics, the atomic-level world where small defects can make a big difference in how particles behave and interact.

As reported in a document in Nature communicationsChong Zu, assistant professor of physics in Arts and Sciences at Washington University in St. Louis, and his team are finding new ways to harness the quantum power of defects in otherwise flawless crystals.

The work is supported in part by the Center for Quantum Leaps, a signature initiative of the Arts & Sciences strategic plan that aims to apply quantum insights and technologies to physics, biomedical and life sciences, drug discovery and other fields of wide scope.

Zu’s lab is examining atomic defects in boron nitride, a material that forms sheets so thin it can be considered two-dimensional. Boron nitride is generally unchanging and uniform but, every now and then, a missing boron atom will leave a tiny gap. These gaps can occur naturally, but Zu and his team, including graduate student Ruotian (Reginald) Gong, accelerated the process by bombarding microscopic flakes of material with helium atoms, tiny atomic projectiles that randomly knock out boron atoms.

The resulting holes have an important quantum potential. The voids naturally fill with electrons which are highly sensitive to their surroundings. For example, small changes in magnetic fields and temperature can change the spin and energy state of electrons. This sensitivity makes them potentially useful as quantum sensors. In the new study, Zu, Gong and colleagues demonstrated for the first time that electrons also react to changes in electric fields, expanding the range of potential applications.

Since these particular sensors are trapped in a thin and stable matrix of boron nitride, they could theoretically be applied to a wide variety of substances, from geological to biological. Other types of sensors are typically created in a vacuum environment that must be cooled to temperatures close to absolute zero.

“You could never put something that cold next to a living cell,” Zu said. Boron nitride sensors, on the other hand, are at room temperature.

Boron nitride sensors could also be used in basic simulation experiments to study the quantum interactions of particles, Zu said. Physicists often use computer programs to predict how particles might interact, she said, but the systems are so complex that even the most powerful computers can only run so fast.

“Instead of trying to build the systems on a computer, you can just build the exact system you want to study and then look at the interactions,” he said.