Now Princeton researchers have developed a diamond-based quantum sensor that reveals rich new information about magnetic phenomena at this minute scale. The technique uncovers fluctuations that are beyond the reach of existing instruments and provides key insight into materials such as graphene and superconductors. Superconductors have enabled today\u2019s most advanced medical imaging tools and form the basis of hoped-for technologies like lossless powerlines and levitating trains.<\/p>\n
The underlying diamond-based sensing methods have been under development for half a decade. But in a Nov. 27\u00a0paper<\/a>\u00a0in\u00a0Nature, the team reported roughly 40 times greater sensitivity than previous techniques.<\/p>\n Nathalie de Leon, associate professor of electrical and computer engineering and the paper\u2019s senior author, said the new technique gives researchers a way to directly observe the structure of \u201cvery small magnetic fields and very small length scales.\u201d That enables unprecedented measurement and reveals details about magnetic fluctuations that hide in the statistical data of more conventional approaches.<\/p>\n \u201cYou have this totally new kind of playground,\u201d de Leon said. \u201cYou just can\u2019t see these things with traditional techniques.\u201d<\/p>\n A New Way to Study Real Quantum Materials<\/p>\n Her team\u2019s new technique is based on engineered defects near the surface of a lab-grown diamond. These diamonds, about the size of a large flake of sea salt, are far purer than natural diamonds, and the defects engineered into them are vanishingly small\u2014one missing atom in a lattice of billions. But because those defects interact strongly with magnetic fields, and because they can be carefully engineered, they make excellent magnetic sensors.<\/p>\n Typically, these sensors are treated as individual points in space. In this latest advance, de Leon and her team built a system that implants two of these defects extremely close together, allowing the defects to interact in quantum-mechanical ways that, to the researchers\u2019 surprise, made the overall system much more capable.<\/p>\n \u201cThat is a very new way of operating this quantum sensor that allows us to probe something which has not been possible before,\u201d said Philip Kim, an experimental physicist at Harvard who was not involved in this study. Other techniques that try to get at this information have been confined to carefully constructed arrays of atoms, not real materials, Kim said. The new technique allows scientists to probe real materials directly. \u201cThat\u2019s where the importance comes in.\u201d<\/p>\n Kim is now working with de Leon using complementary techniques in his lab, where he studies condensed matter physics. Specifically, he looks at superconductors that can be cooled by liquid nitrogen to their critical temperatures, and graphene, a material that promises fantastical-seeming uses but that has proven difficult to engineer at scale.<\/p>\n Quantum Entanglement Reveals Signals in the Noise<\/p>\n To create the new sensor, the researchers fired nitrogen molecules traveling more than 30 thousand feet per second at the diamond. When a molecule strikes the diamond\u2019s famously hard surface with that much energy, the molecule breaks apart, sending its two nitrogen atoms\u2014no longer chemically bonded\u2014hurtling in separate directions into the diamond\u2019s crystalline structure.<\/p>\n By precisely controlling how much energy the molecule has when it slams into the diamond, the researchers can control how deep the nitrogen atoms penetrate. In this case, they drill past a few dozen carbon atoms and stop about 20 nanometers beneath the surface, coming to rest roughly 10 nanometers apart from each other.<\/p>\n That exceedingly small separation allows the two atoms to interact with each other in ways that give rise to quantum entanglement, a property so foreign to human experience that Albert Einstein once derided it as \u201cspooky action at a distance.\u201d<\/p>\n When entangled, the electrons in these two nitrogen atoms begin to act in lock step. The measurement of one reveals a perfectly correlated measurement in the other. Because they still represent distinct points, like two eyes, the entangled sensors can triangulate signatures in the noisy fluctuations and effectively home in on the source of the noise.<\/p>\n At this size range, between the atomic scale and the wavelength of visible light, de Leon said scientists want to measure previously invisible quantities, like how far an electron travels through a material before bouncing off another particle, or the evolution of magnetic vortices that appear in superconducting materials under special conditions.<\/p>\n \u201cThat range is, in fact, the length scale of interest,\u201d Kim said. \u201cA good range where one can understand a lot of interesting things.\u201d<\/p>\n A Weakness in the Sensor Leads to Quantum Advantage<\/p>\n The breakthrough that led to this entangled sensor came from Jared Rovny, who began working with de Leon in 2020 as one of the inaugural Princeton Quantum Initiative postdoctoral fellows.<\/p>\n The COVID-19 pandemic had curtailed access to the lab when Rovny started. So, like many of his peers, he set to work on ideas that did not require in-person, experimental setups. He and de Leon decided to dig into the theory around magnetic noise and see if there were ways to use the diamond defects\u2014called nitrogen vacancy centers\u2014to detect correlations in the magnetic noise that hums in the background of condensed matter physics.<\/p>\n \u201cIt started as one of these weird, COVID, theory projects,\u201d de Leon said. At the time, sensing correlations in magnetic noise was not a topic of scientific conversation, she said. In fact, they started the project out of pure curiosity, not sure where it would lead. \u201cIt was only after we started formalizing it that we realized how powerful it was.\u201d<\/p>\n Rovny had a background in nuclear magnetic resonance, or NMR, in which interacting particles and their correlations were key to his research. This fed his curiosity and allowed the project to take a more serious turn.<\/p>\n \u201cThat NMR side of me was really always thinking about interactions,\u201d Rovny said. \u201cThere were a bunch of different physics ideas I wanted to explore that had to do with interacting these things, not leaving them separate.\u201d He is now a physicist at quantum computing startup Logiqal.<\/p>\n At first, working in collaboration with Shimon Kolkowitz, an atomic physicist at University of Wisconsin-Madison (now at University of California-Berkeley), they\u00a0looked at correlations<\/a>\u00a0between two centers that were not entangled. While those methods led to interesting findings, and a 2022 paper in\u00a0Science, they were also technically onerous and prohibitively complex for most experimental uses.<\/p>\n \u201cWhat I realized is that if you entangled them,\u201d Rovny added, referring to the nitrogen vacancy centers, \u201cthe presence or absence of a correlation sort of puts its fingerprint onto the system.\u201d<\/p>\n That fingerprint allowed them to bypass the most cumbersome problems and gave them the advantage of two sensors with roughly the same cost of using only one.<\/p>\n \u201cNow all I have to do is a single measurement,\u201d de Leon said, \u201ca single normal measurement.\u201d<\/p>\n![\"Responsive](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/10\/Website-Banner-Quantum-2.gif\")
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Nathlie de Leon is a leader in diamond-based quantum sensing. Credit: Princeton University; Office of\u2026<\/p>\n