Exploiting diamond imperfections opens a new frontier in the development of quantum sensors

Quantum defects have the potential to act as ultra-sensitive sensors that could offer new types of navigation or biological sensor technologies.

One type of these defect systems, nitrogen vacancy (NV) centers in diamonds, can measure magnetic fields on the nanoscale. But even if scientists can control the quantum spin of these centers (unique defects in diamond, where nitrogen has replaced carbon), they still don’t understand how best to isolate that spin from the spins of other defects in the material. . which can destroy its quantum state memory, or its coherence.

Only by studying exactly how this material works at the atomic level can scientists and engineers realize the potential of these sensors. In new research at the University of Chicago’s Pritzker School of Molecular Engineering (PME), researchers in Professor David Awschalom’s lab have developed a new way to exploit defect spin to measure the behavior of other unique electronic defects in diamond.

This new understanding, published in Physical Examination Letterswill be used to create even better quantum sensors capable of maintaining long coherence times.

“We designed a way to observe certain behaviors of unique quantum spin states that otherwise would have proven elusive to standard measurements,” Awschalom said. “This will impact both how we design quantum systems and how we think about charge in many materials.”

Find a way to measure background noise

Led by PME Ph.D. graduate and current postdoctoral researcher Jonathan Marcks, the research team is synthesizing these NV centers at the Argonne National Laboratory facility. They grow the diamond layer by layer using chemical vapor deposition and can introduce only a few nanometers of nitrogen dopants to create unique NV centers.

These single spin defects are very coherent, but their spin remains sensitive to the behavior of other defective spins in the material. Indeed, no matter how carefully the diamond is grown, it always ends up exhibiting unintentional nitrogen defects that have their own spin. This causes decoherence in the system, affecting its usefulness as a sensor.

“Even though we have good control over where we put the nitrogen, we still end up with this background noise,” Marcks said. “Because we want to develop highly coherent nitrogen vacancy centers, we wanted to better understand how these surrounding defects behave and couple to each other.”

Measuring a nearby electronic charge

To better understand these unique electronic defects in nitrogen, the team used a laser and a home-made microscope system to measure the NV center. The number of photons emitted by the NV center depends on the rotation state of the NV center. Because these centers interact with other spins, the team realized they could use the NV center as a nanoscale sensor of the electronic charge of nearby nitrogen, which would otherwise be invisible.

The process gave them the first-ever observation of coupled spin and charge dynamics within this material, down to single defects.

“We expected that the nitrogen defects would all have only one charge state, but they actually reverse and are not always in the same charge state,” Marcks said. “It’s different from what we assumed about solid-state physics.”

The team partnered with Professor Aashish Clerk and Professor Giulia Galli, whose teams provided the theoretical and computational tools allowing the researchers to better understand their observations.

Ultimately, the team will use this knowledge not only to better understand the behavior of these material systems, but also to build better quantum sensors.

“By combining experiment, theory and calculation, we have ideas on how to create extremely clean materials for emerging quantum technologies and control some of these internal noise sources,” Galli said.

Other authors of the paper include Mykyta Onizhuk, Yu-Xin Wang, Yizhi Zhu, Yu Jin, Benjamin S. Soloway, Masaya Fukami, Nazar Delegan, and F. Joseph Heremans.