NMR spectroscopy
Purdue Researchers Use 2D Materials to Reach Atomic-Scale Resolution in Quantum Sensing
Purdue University researchers have advanced quantum sensing significantly by creating a method that may enhance nuclear magnetic resonance (NMR) spectroscopy down to the atomic level. Utilizing rare carbon-13 isotopes and two-dimensional (2D) materials, this breakthrough has broad ramifications for the study of biological molecules as well as the creation of next-generation quantum computing and communications systems.
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From MRI to Atomic Resolution: Overcoming Conventional Limitations
The innovation expands on the same ideas that underpin traditional NMR spectroscopy, a method for examining biological molecules in illness and treatment research, and Magnetic Resonance Imaging (MRI), which is utilized for medical diagnostics. The small magnetic fields produced by some atoms’ nuclei, such as the single proton in a hydrogen nucleus, that are impacted by their surroundings are used by both MRI and NMR. These methods involve flipping these nuclei with radio waves, and the signals that are released when they align again reveal details about their environment.
Conventional NMR spectroscopy, which usually operates at a resolution of 100 micrometers and requires huge, milligram-sized samples, is useful for learning about molecular structures, but it lacks the resolution to detect individual atoms. The goal of this new study was highlighted by Purdue professor Tongcang Li, who stated: “Conventional NMR spectroscopy is limited to measuring large samples of molecules.” Our goal is to create technologies that are capable of detecting and analyzing a single molecule.
2D Materials and Spin Defects: A Novel Approach
By applying the magnetic resonance principle to 2D materials sheets of atoms that are just a few atoms thick, Li’s lab is leading the way in this development. This novel arrangement uses spin defects, specifically created flaws in the 2D material, to provide information on the structure of biological molecules that are deposited directly on top of the material. Because the molecule and the 2D material are so close, the biological sample’s atoms affect the spin defects, changing the magnetic resonance signal and revealing structural details at the atomic level.
Hexagonal boron nitride (hBN), which is made up of alternating boron and nitrogen atoms in a hexagonal lattice, is the selected 2D material. Where an atom is absent, there are vacancies, or natural defects. Li’s team used electrons in boron vacancies as quantum sensors to regulate and gather data from nearby nitrogen nuclei in earlier research that was published in 2022. They were able to achieve a resolution of 1 micrometer. This was still not the single-nucleus resolution needed for individual atom identification, although it was noticeably superior to traditional NMR.
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The Carbon-13 Breakthrough
Li’s team investigated carbon flaws in hBN in an effort to obtain a greater resolution. They looked to carbon-13, a rare isotope with an extra neutron that allows it to produce a magnetic field appropriate for magnetic resonance applications, because regular carbon lacks a magnetic field.
The scientists used a specific procedure to insert these important carbon-13 flaws. After using a carbon dioxide gas that was 99% carbon-13 enriched, they used an electric field to accelerate the atoms, essentially blasting them at a hBN sample. In the hBN crystal lattice, this reaction led to the displacement of certain boron or nitrogen atoms by carbon-13 and oxygen atoms. Using optical microscopy, the scientists verified the sites of these novel carbon-13-containing flaws.
The crucial step was to ascertain the intricate nature of these recently formed flaws within the hBN lattice by employing the carbon-13 nucleus itself as a probe. They obtained signals from the carbon-13 nucleus that gave them specific details about its near surroundings by using a method known as optically detected nuclear magnetic resonance. The single-spin NMR spectroscopy of a carbon-13 nuclear spin in a two-dimensional substance has never been done before.
The researchers successfully determined the exact structures of flaws in two of the three categories into which they categorized the faults, working with Yuan Ping, a theorist from the University of Wisconsin-Madison.
Quantum Applications and Future Prospects
One important discovery was that, even at ambient temperature, the nuclear spin of carbon-13 shows a lengthy coherence time. For applications involving quantum computing, where preserving quantum states for prolonged periods of time is essential, this property is extremely beneficial.
“This is the first time that a spin defect in hexagonal boron nitride has been created using carbon 13,” Li said. Our research contributes to a better understanding of hexagonal boron nitride spin defects and offers a means to use nuclear spins as quantum memory to improve quantum sensing. This research has potential applications in quantum sensing and quantum communications in addition to quantum computing.
The U.S. Department of Energy, the National Science Foundation, and the Gordon and Betty Moore Foundation all provided funding for this ground-breaking study.
About Purdue University
One of the top ten public universities in the US, Purdue University is renowned for its quality and scope in knowledge discovery, dissemination, and application. Purdue has maintained a tuition freeze for 14 years running, demonstrating its dedication to affordability and accessibility.
The university has approximately 107,000 students spread among several locations and modes, including more than 58,000 at its main campus in West Lafayette and Indianapolis. In addition to being a member of the Purdue Quantum Science and Engineering Institute, Tongcang Li is the director of the National Science Foundation’s Industry-University Cooperative Research Centre for Quantum Technologies in Indiana. He is a professor of electrical and computer engineering in the College of Engineering and physics and astronomy in the College of Science.
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