Semiconductor Defects Could Boost Quantum Technology

Defects are the best friends of quantum sensors in diamonds (and others Semi-insulating material).

This is because defects, which are essentially a jumbled arrangement of atoms, sometimes contain electrons with angular momentum or spin, which can store and process information. These “spin degrees of freedom” can be used for various purposes, such as sensing magnetic fields or building quantum networks.

Doctoral students Jialon Lu (left) and Greg Fuchs, Ph.D. ’07, a professor of applied and engineering physics at Cornell Engineering, searched for “spin degrees of freedom” in the popular semiconductor gallium nitride and surprisingly found it in two distinct species. Photo credit: Charissa King-O’Brien/Cornell Engineering

Led by researchers Greg Fuchs, Ph.D. ’07, professor of applied and engineering physics at Cornell Engineering, went looking for such spins in the popular semiconductor gallium nitride and surprisingly found them in two distinct species, one of which has potential future quantum applications. Can be used for

The group’s paper, “Room temperature optically detected single spin magnetic resonance in GANPublished in Nature Materials. Lead author is doctoral student Jialon Luo.

Flaws are what give gems their color, and that’s why they’re also called color centers. For example, pink diamonds get their color from defects called nitrogen vacancy centers. However, there are many color centers that have yet to be identified, even in commonly used materials.

“Gallium nitride, unlike diamond, is a solid semiconductor. It’s been developed for wide-bandgap high-frequency electronics, and it’s been a very intense effort for many years,” Fuchs said. You can buy a wafer for it, it’s in your computer charger, maybe, or an electric car. But in terms of materials for quantum defects, it has not been explored much.

To explore the spin degrees of freedom in gallium nitride, Fuchs and Luo worked together. Farhan Rana, Joseph P. of Engineering. Ripley professor, and doctoral student Yifei Geng, with whom he previously explored the material.

The group used confocal microscopy to identify defects with fluorescent probes and then performed a number of experiments, such as measuring how the fluorescence rate of a defect changes as a function of a magnetic field. and using a small magnetic field to drive the defect’s spin resonance transmission, all at room temperature.

“Initially, the preliminary data showed signs of interesting spin structure but we couldn’t drive the spin resonance,” Luo said. “It turns out that we needed to know the symmetry axes of the defect and apply a magnetic field with the right direction to check the resonance; the results brought us more questions, waiting to be worked out. are doing

Experiments showed that the material had two types of defects with distinct spin spectra. In one, the spin was coupled to a metastable excited state. In another, it was linked to the ground state.

In the latter case, the researchers were able to see fluorescence changes of up to 30% when they drove the spin transition – a large change in contrast, and relatively rare, for a quantum spin at room temperature.

“Usually fluorescence and spin are very weakly coupled together, so when you change the spin projection, the fluorescence can change by 0.1 percent, or something much smaller,” Fuchs said. “From a technology perspective, it’s not great, because you want a big change, so you can measure it quickly and efficiently.”

The researchers then experimented with quantum control. They found that they could manipulate the spin of the ground state and that it had quantum coherence — a quality that allows quantum bits, or qubits, to retain their information.

“That’s something that’s very interesting about this observation,” Fuchs said. “There is still a lot of fundamental work to be done, and more questions than answers. But the fundamental finding of the spin in this color center, the fact that it has a strong spin contrast of up to 30%, is that it is a solid semiconductor material. exists in—that opens up all kinds of exciting possibilities that we’re now excited to explore.”

Source: Cornell University