Atomic defects form quantum emitters in hBN

SOPHIA CHEN: Many researchers are hotly anticipating quantum technology, a new paradigm that exploits the mathematics of quantum mechanics. But researchers are still developing the so-called quantum materials to build these devices and connect them in a future quantum internet. Jennifer Dionne, a materials scientist at Stanford University, is investigating one such material called hBN, or hexagonal boron nitride. hBN could be useful for quantum machines because it can be made to emit single photons of light to compute and transmit information. When you illuminate hBN with light the material will emit a spectrum of colors ranging from the red to the green. Dionne’s team wanted to understand what microscopic property or defect in the material was responsible for the different colors. 

JD: What we wanted to do was address where those different colors were coming from, because in a future quantum optical network, ideally you’d be able to control what color is coming out where and be able to use that wavelength multiplexing of photonic communications.

SC: To identify which light came from what defect, they used a combination of two different techniques. 

JD: By interrogating with an optical microscope, we can see broadly where there were different defects and use the electron microscope to zoom into those defects and map them out with much higher resolution and to also look at their atomic scale structure.

SC: They were able to identify that the colors arise from four classes of defects in the hexagonal boron nitride.

JD: So we now know with certainty there are at least four different types of atomic defects that are responsible in the main spectral windows. If you want light predominantly in the green, you would use one type of atomic defect. If you want light in the red, you use a different type of atomic defect.

SC: Combining their experimental studies with theory, Dionne’s team was able to deduce more details about the defects themselves.

JD: We found that it seems like most of the defects that are emitting are not simple atomic defects, but rather complexes. So hexagonal boron nitride, like I said, is this layered material. You need to think not only about a missing atom in one layer but perhaps a missing atom or a substitutional atom in a neighboring layer, and basically a series of missing atoms between one layer and a next form something like its own independent molecule in the material.

SC: By understanding the specific defects in a material, eventually, researchers should be able to implant specific impurities that can be independently controlled to emit light in a quantum device.

JD: We’re excited to get higher spatial imaging resolution and start positioning those emitters and see how we might be able to modulate the emission, to be able to turn the emission on off, which would be the same in a transistor. You want to be able to turn the electrical current on and off and be able to get gain. Trying to create a suite of quantum optical devices based on these emitters would be very exciting and next step.

SC: But this technique, where they combine optical and electron microscopy to study quantum materials, is useful beyond just hexagonal boron nitride.

JD: More so than learning about hexagonal boron nitride, I think the significance of our paper is that it provides a technique to be able to do this correlation of the atomic scale structure of quantum materials with their optical properties.