They say you can miss the forest for the trees. But it is often worth taking a closer look at the trees to understand how thick and hairy they are. Here’s what a group at Stanford University did to solve the complex quantum information problem in diamond.

As a star material for hosting quantum information, diamond still poses a problem: signals from quantum information particles embedded in diamond are often complex and contradictory. Scientists offered an explanation for the discrepancy, but they needed a way to examine the diamond’s components to determine the culprit.

A Stanford group led by Jennifer Dionne did just that by magnifying the structure of diamond at the atomic level using a powerful microscope. In the article published in PNASThe team showed that the diamond’s colorful interior largely explains the chaotic signals from embedded quantum bits.

“There was no good way to relate the structure of the qubit (the quantum bit) to the emitted signal, but the researchers observed significant heterogeneity in the emission,” said Dionne, associate director of Q-NEXT and a professor at Stanford. University. materials science and courtesy radiology. “We solved the problem by relating atomic-scale structure to quantum properties.”

silicone gap

The group worked with a type of qubit called a silicon cavity center. Two carbon atoms are removed from the diamond and replaced with a silicon atom. Since two atoms are replaced by one atom, the silicon atom has a void (a half-filled hole) on each side.

Silicon void hubs hold promise for quantum sensors that can achieve many orders of magnitude higher sensitivity than today’s best devices, and quantum communications networks that are virtually immune to eavesdropping due to their quantum nature.

Dionne’s group tested silicon vacancy centers in diamond nanoparticles, which are tiny pieces of diamond a few hundred nanometers in diameter. As a rule, several voids are scattered throughout the sample, like holes in a sponge.

The signal from the cavity center takes the form of a photon, a particle of light. In an ideal world, a hole in the diamond would act as a reliable photon factory, reliably producing the same type of photons, the same color, the same brightness every time they roll off the assembly line.

“We need indistinguishable photons,” said the paper’s first author, Daniel Angell, who conducted the research as a graduate student at Stanford University.

However, scientists observed that the photons emitted from diamond sources have different colors and brightness. This forced Dionne’s group to dig deeper.

The versatility of a diamond

A diamond is something colorful. Like most crystals, diamonds consist of irregularly shaped domains that bump into each other like Lego bricks. Regions or fields are distinguished by their atomic “grains”, like the grain of a tree. One area with diagonally arranged atoms may be adjacent to another with a front-to-back orientation.

The team used a scanning transmission electron microscope to examine the areas individually and measure the photon emission from each; This was an extremely delicate task that would have been nearly impossible with a less powerful device. They began to notice a pattern.

“We kept looking at these diamonds, and eventually we could start to see really steep, very different regions of photon emission; the photon profile would be different from one region to the next,” Angell said.

The conclusion was clear: Fields matter.

The grain of each field creates a space within itself by stretching or compressing it. While vacancy in one area may be stressed in one direction, vacancy in a neighboring house may be stressed in another way. The group found that the way the void is stressed affects the properties of the emitted photon, as does its location in the grain structure.

Scientists measured blurred or inconsistent signals from the diamond because they viewed the sample as a single source, a single emitter of photons. But a diamond sample contains several tightly packed domains, each containing its own photon emitter. The researchers measured the signal from the forest, not the trees.

“The location of the void in the crystal is important,” Dionne said. “The different crystal faces of a diamond and the particular orientation of the crystal can have a significant effect on both the brightness and color of the radiation.”

Even empty spaces located a short distance apart can produce significantly different photon emissions.

“We observed a completely separate jump in the emission signal when the two vacancies were only 5 nanometers apart,” Angell said. “Seeing this almost perfect dividing line between emissions at the nanoscale – a distinct change in emissions – is something I’ve never seen before. “This is really interesting data to consider.”

crystal clear

Angell correlated different types of grain deformations with corresponding photon profiles, providing the researchers with a high-resolution map of deformation and radiation to better understand their findings. Although particle type is not the only factor affecting fuzzy photonic signals, Dionne’s group showed that it plays an important role.

“We note that it’s important to know exactly the fundamental grain structure of the crystalline particles under study. If you’re collecting radiation from the entire particle and you have fuzzy radiation, it’s probably because they have some sort of grain boundary. You’re getting different jobs with different signatures and you don’t know it,” Angell said.

His work also has a broader scope, encompassing other members of the qubit family of work centers.

“It has opened the door to a wealth of research that provides precise correlations between structure and function in quantum systems, ultimately improving quantum communications, quantum networking and quantum sensing,” Dionne said.