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The realm of quantum mechanics is inherently enigmatic, but what occurs when this peculiar domain of subatomic particles is subjected to immense strain? Observing quantum phenomena under pressure has been challenging for a straightforward reason: Crafting sensors that can endure extreme forces is complex.
In a notable breakthrough, a group spearheaded by physicists at WashU has developed quantum sensors embedded in a resilient layer of crystallized boron nitride. These sensors can gauge stress and magnetic fields in materials under pressures surpassing 30,000 times that of the atmosphere.
“We’re the pioneers in creating this type of high-pressure sensor,” stated Chong Zu, an assistant professor of physics within Arts & Sciences and a member of Washington University in St. Louis’ Center for Quantum Leaps. “This could have diverse applications across various disciplines, including quantum technology, material science, astronomy, and geology.”
The team detailed their discovery in the esteemed journal Nature Communications. Co-authors of the paper include graduate students from Zu’s lab, among them Guanghui He, Ruotian “Reginald” Gong, Zhongyuan Liu, and Changyu Yao; along with graduate student Zack Rehfuss; postdoctoral researcher Mingfeng Chen; as well as Xi Wang and Sheng Ran, both assistant professors in the field of physics.
This research was partially funded by a National Science Foundation Research Traineeship (NRT) grant, which enabled He to spend six months at Harvard University collaborating with physicist Norman Yao, also a paper co-author.
To construct the sensors, the team utilized neutron radiation beams to displace boron atoms from the thin layers of boron nitride. The resulting vacancies can immediately capture electrons. Due to quantum interactions, these electrons alter their spin energies based on local magnetism, stress, temperature, and other characteristics of nearby materials. Monitoring the spin of each electron yields profound insights into the material under examination.
Zu and his team had previously generated quantum sensors by creating vacancies in diamonds, which support WashU’s two quantum diamond microscopes. Although effective, diamond sensors come with a limitation: As diamonds occupy three-dimensional space, positioning the sensors close to the material being examined is challenging.
Conversely, layers of boron nitride can be thinner than 100 nanometers — roughly 1,000 times slenderer than a human hair. “Since the sensors are situated in a material that is essentially two-dimensional, there’s less than a nanometer (a billionth of a meter) separating the sensor from the material it’s analyzing,” Zu noted.
Diamonds remain crucial in this research. “To assess materials under extreme pressure, we need to place the sample on a platform that won’t shatter,” He clarified.
Being the hardest known substance, diamonds fulfill this role. He and other members of the Zu lab developed “diamond anvils” — two flat diamond surfaces, each approximately 400 micrometers wide, roughly equivalent to the thickness of four dust particles — which press together in a high-pressure chamber. “The simplest method to generate high pressure is by applying significant force on a small surface area,” He elaborated.
Experiments demonstrated that the new sensors could detect minute alterations in the magnetic field of a two-dimensional magnet. Looking ahead, the researchers intend to investigate other materials, including samples of rocks similar to those existing in the extreme-pressure conditions of the Earth’s core. “Assessing how these rocks react to pressure could enhance our understanding of earthquakes and other large-scale phenomena,” Zu explained.
The sensors could also propel advancements in superconductivity, the ability to transmit electricity without resistance. Presently, known superconductors necessitate exceptionally high pressures and low temperatures. Past assertions that certain materials might function as superconductors at room temperature have sparked considerable controversy. “With this type of sensor, we can gather the crucial data needed to resolve the ongoing debate,” stated Gong, who, alongside He, co-led the paper.
Zu emphasized the significance of the NSF NRT training grant in this research. “The initiative fosters collaboration among universities,” he mentioned. “Now that we possess these sensors, the high-pressure chamber, and the diamond anvils, we will have enhanced opportunities for investigation.”
Originally published on the Ampersand website.
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