Defects responsible for messy behavior in quantum materials

In a future built on quantum technologies, planes and spaceships could be fueled by the momentum of light. Quantum computers will crunch through complex problems spanning chemistry to cryptography with greater speed and energy efficiency than existing processors. But before this future can come to pass, we need bright, on-demand, predictable sources of quantum light.

Toward this end, a team of Stanford University material scientists, physicists and engineers, in collaboration with labs at Harvard University and the University of Technology Sydney, have been investigating hexagonal boron nitride, a material that can emit bright light as a single photon – a quantum unit of light – at a time. And it can do this at room temperature, making it easier to use compared to alternative quantum sources.

Unfortunately, hexagonal boron nitride has a significant downside: It emits light in a rainbow of different hues. “While this emission is beautiful, the color currently can’t be controlled,” said Fariah Hayee, the lead author and a graduate student in the lab of Jennifer Dionne[1], associate professor of materials science and engineering at Stanford. “We wanted to know the source of the multi-color emission, with the ultimate goal of gaining control over emission.”

By employing a combination of microscopic methods, the scientists were able to trace the material’s colorful emission to specific atomic defects. A group led by co-author Prineha Narang, assistant professor of computational materials science at Harvard University, also developed a new theory to predict the color of defects by accounting for how light, electrons and heat interact in the material.

“We needed to know how these defects couple to the environment and if that could be used as a fingerprint to identify and control them,” said Christopher Ciccarino, a graduate student in the NarangLab at Harvard University and co-author of the paper.

The researchers describe their technique and different categories of defects in a paper[2] published in the March 24 issue of the journal Nature Materials.

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