Traditional nuclear magnetic resonance spectroscopy, familiar to many through its medical imaging counterpart—magnetic resonance imaging (MRI)—has revolutionized our ability to visualize internal structures non-invasively. Yet, the inherently limited resolution of conventional NMR has imposed a boundary on examining molecular structures at the atomic scale. Diagnostic MRI and standard NMR methods require large ensembles of atoms to produce signals, preventing scientists from observing single molecules or even individual atoms. This limitation has been an enduring obstacle in both fundamental research and applications demanding unparalleled precision, such as quantum computing components and highly sensitive molecular sensors.

Li’s team has capitalized on the unique qualities of 2D materials, which form crystalline sheets just atoms thick. Hexagonal boron nitride, specifically, exhibits a lattice structure of alternating boron and nitrogen atoms arranged in hexagonal rings and hosts naturally occurring vacancies—missing atoms that create localized sites capable of trapping electrons or nuclear spins. By introducing carbon-13 isotopes into these vacancies, the researchers transformed these sites into controllable spin defects. Unlike its most abundant isotope, carbon-12, carbon-13 has a nuclear spin that interacts with magnetic fields, enabling it to be directly probed by magnetic resonance techniques.

The process of embedding carbon-13 isotopes into hBN involved a sophisticated technique where carbon-13-enriched carbon dioxide gas was accelerated toward the hBN crystal using an electric field, causing some atoms to replace boron or nitrogen atoms in the lattice. These substitutions created a new class of spin defects that serve as sensitive probes of their atomic surroundings. By exploiting optically detected NMR, a method that couples nuclear magnetic resonance with optical readout through emitted photons, Li’s group succeeded in achieving single-spin detection. This approach allows the direct observation of the quantum state of a single nuclear spin in a material only a few atoms thick—a feat never accomplished before.

One of the hallmark achievements of this study is the ability to classify the newly discovered spin defects into three distinct groups based on their characteristic spectroscopic signals. Collaborating with theorist Yuan Ping from the University of Wisconsin-Madison, the team combined experimental observations with advanced computational modeling to identify the specific atomic structures corresponding to two of these groups. These insights are crucial because understanding the precise defect geometry is fundamental for reproducible quantum device engineering and for tuning the coherence properties of spin qubits.

Coherence time, or how long a quantum state remains unperturbed, is a critical parameter for quantum technologies. Remarkably, the carbon-13 spin defects in hBN demonstrated long coherence times even at room temperature, an attribute that positions these defects as promising quantum memories. Quantum memories are the backbone of many quantum computing and communication schemes, storing quantum information reliably during processing and transmission. The discovery that these nuclear spins maintain coherence without requiring cryogenic cooling represents a major leap toward practical quantum devices operating under ambient conditions.

The implications of this advancement extend beyond the realm of quantum computing. Magnetic resonance microscopy enhanced with atom-scale resolution can revolutionize molecular analysis by enabling the direct detection and structural characterization of individual biological molecules. This capability opens up possibilities for unprecedented insight into protein folding, enzyme mechanisms, and pharmacological interactions at the ultimate level of detail, potentially transforming drug discovery and molecular diagnostics.

Historically, Li’s research group has pursued using the electron spins in boron vacancies within hBN as quantum sensors. While these electron spins emitted light to signal local magnetic environments, their optical emission was too weak for single-defect resolution. The pivot toward carbon-13 nuclear spins represents a strategic evolution, overcoming the sensitivity barrier by directly targeting nuclear rather than electronic spins, which are less prone to environmental noise and thus capable of longer coherence times.

The sophisticated interplay between nuclear and electron spins in these 2D materials allows for precise manipulation and readout of quantum states using combinations of magnetic resonance and optical techniques. Optically detected nuclear magnetic resonance uniquely enables this control by using laser excitation to polarize and detect nuclear spins indirectly via changes in emitted light, thus merging the strengths of optical measurement with the intrinsic information contained in nuclear spins.

This research was enabled by meticulous experimental craftsmanship combined with theoretical expertise, supported by funding from the Gordon and Betty Moore Foundation, the U.S. National Science Foundation, and the Department of Energy. By revealing the pathways to harness individual nuclear spins in scalable and accessible materials like hexagonal boron nitride, the study marks a transformative moment in quantum science, where the manipulation of matter at the smallest scales can translate into revolutionary technologies.

Looking forward, the ability to deterministically place and control carbon-13 spin defects promises the creation of quantum sensors of unparalleled sensitivity and spatial resolution. These detectors could transform a wide array of scientific disciplines, ranging from nanoscale magnetic resonance imaging to quantum-enhanced biological sensing. Moreover, the research enriches the toolbox for engineering novel qubits in 2D materials, essential for developing scalable quantum networks that integrate with existing semiconductor technology.

In summary, Purdue University’s recent demonstration of single nuclear spin detection and precise control in hexagonal boron nitride heralds a new era of quantum sensing and molecular microscopy. By weaving together the subtle intricacies of materials science, quantum physics, and cutting-edge spectroscopy, this work not only solves a longstanding challenge in NMR spectroscopy but also lays the groundwork for breakthroughs in quantum computing, communications, and biomedical research—ushering us ever closer to the long-envisioned realm of atomic-scale exploration and manipulation.

Subject of Research: Not applicable

Article Title: Single nuclear spin detection and control in a van der Waals material

News Publication Date: 9-Jul-2025

Web References:

• Article in Nature: https://www.nature.com/articles/s41586-025-09258-7
• Purdue Physics Faculty: https://www.physics.purdue.edu/people/faculty/tcli.php
• Purdue Quantum Science and Engineering Institute: https://quantum.research.purdue.edu/
• Purdue National Science Foundation’s Quantum Technologies Center: https://www.purdue.edu/cqt/
• Purdue Strategic Initiatives: https://www.purdue.edu/president/strategic-initiatives

References:
Li, T., et al. “Single nuclear spin detection and control in a van der Waals material.” Nature (2025). DOI: 10.1038/s41586-025-09258-7

Image Credits: Purdue University photo/Charles Jischke

Keywords:

• NMR spectroscopy
• Quantum information
• Qubits

For decades, the pursuit of quantum sensing excellence has been hindered by the inherent fragility of quantum states. Decoherence—random scrambling of a quantum system’s state due to environmental interactions—acts as the primary adversary, erasing coherent quantum signals and shrouding subtle physical phenomena in noise. Addressing this issue, the team, led by Eli Levenson-Falk, associate professor of physics and electrical engineering at USC, has developed a novel coherence-stabilized sensing protocol that ingeniously counters decoherence’s debilitating effects without relying on complex feedback or resource-intensive controls.

Quantum sensors utilize the unique properties of quantum bits, or qubits, such as superposition, entanglement, and coherence, to detect infinitesimal signals that classical devices cannot resolve. These sensors hold the key to unlocking a new era of precise measurements—ranging from detecting brain activity patterns and gravitational anomalies to enabling ultra-precise timekeeping. However, the persistent challenge of decoherence, where quantum states degrade and lose their exquisitely delicate information, has placed a stubborn ceiling on sensor sensitivity.

The innovation introduced by the USC researchers pivots on a carefully designed, predetermined coherence stabilization protocol. By stabilizing a crucial property of the qubit’s quantum state, the protocol effectively postpones its decay toward the “north pole” on the Bloch sphere—an abstract representation of qubit states. This stabilization strategy is rooted in theoretical formulations conceived by co-authors Daniel Lidar, a Viterbi professor of engineering, and Kumar Saurav, a doctoral student in electrical engineering. Their work fundamentally rethinks how quantum state dynamics can be controlled deterministically to enhance measurement fidelity.

Instead of allowing the quantum state’s coherence to deteriorate unpredictably, the team’s coherence-stabilized protocol maintains the qubit in an optimized trajectory that amplifies the sensing signal—particularly the ‘y’ component of the qubit’s Bloch vector representation—well beyond what standard approaches achieve. This results in a significantly larger, more detectable quantum sensing signal that grows during measurement, thereby increasing overall sensitivity.

A key advantage of this new protocol is its simplicity and practicality. Conventionally, achieving improved quantum sensing calling for real-time feedback mechanisms or additional measurement resources has hampered scalability and utility in real-world scenarios. The USC method eschews such demands, requiring neither complex feedback loops nor supplementary control pulses. This translates into seamless integration potential across many existing quantum computing architectures and sensing platforms.

Experimentally, the researchers demonstrated their protocol on a superconducting qubit system—a leading technology in the current era of noisy intermediate-scale quantum devices. Their results showcased an enhancement in sensitivity of up to 165% per measurement compared to the traditional Ramsey interferometry method, the canonical technique used to detect frequency shifts in quantum systems. Theoretical projections suggest even greater improvements, nearing a factor of 1.96, could be achieved in optimized configurations.

This leap in sensitivity is more than a numeric milestone. It indicates that the boundaries of quantum sensing can be pushed further by harnessing deterministic quantum state control, unveiling richer information previously lost within noisy measurements. Eli Levenson-Falk emphasized that these findings point to untapped avenues for refining sensing strategies, potentially making quantum sensors far more robust and versatile in detecting subtle signals from nature.

The implications of such advancements ripple through both fundamental science and practical engineering. Enhanced quantum sensors could revolutionize precision measurements in magnetic fields, gravitational variations, and biological processes, laying the groundwork for breakthroughs in navigation, healthcare diagnostics, and beyond. Furthermore, improved coherence preservation dovetails with efforts to scale up quantum processors, where fragile qubit states must be maintained long enough for complex computation.

One of the profound outcomes of this research is demonstrating that enhanced quantum sensing need not hinge on complicated, resource-heavy mechanisms. Instead, carefully planned deterministic control sequences can amplify the usable quantum signal directly. This represents a paradigm shift—from reactive feedback to proactive state design—potentially simplifying quantum sensor development and accelerating its deployment in diverse technologies.

The research team credits the fruitful collaboration between theorists and experimentalists in realizing this concept. The confluence of precise quantum control theory and state-of-the-art superconducting qubit fabrication, supported by institutions such as the U.S. Army Research Laboratory and the National Science Foundation, underscores the interdisciplinary nature of cutting-edge quantum science.

Looking forward, the study’s insights pave the way for exploring even more sophisticated coherence stabilization schemes and for extending these principles to other quantum platforms, such as trapped ions or nitrogen-vacancy centers in diamond. The quest to extract every ounce of information from fragile quantum states continues, with this breakthrough marking a pivotal milestone toward that goal.

Ultimately, the USC team’s achievement reflects the vibrant progress in quantum information science, where theoretical ingenuity and experimental prowess synergize to push technology closer to the quantum limits of measurement. With improved sensitivity and operational simplicity, such innovations promise to unlock new horizons in both the exploration of the quantum world and the development of transformative applications.

Subject of Research: Quantum sensing and coherent qubit control

Article Title: Beating the Ramsey limit on sensing with deterministic qubit control

News Publication Date: 29-Apr-2025

Web References:
https://www.nature.com/articles/s41467-025-58947-4
http://dx.doi.org/10.1038/s41467-025-58947-4

References:
Hecht M.O., Saurav K., Vlachos E., Lidar D.A., Levenson-Falk E.M. (2025). Beating the Ramsey limit on sensing with deterministic qubit control. Nature Communications. DOI: 10.1038/s41467-025-58947-4.

Image Credits: Eli Levenson-Falk/USC

Keywords

Quantum information science, Sensors, Environmental methods, Theoretical physics, Quantum computing, Qubits, Quantum processors, Superconduction, Quantum measurement, Quantum dynamics, Quantum limits, Quantum states, Quantum phase transitions, Particle physics, Magnetic fields

The foundational principle of this novel technique resides in the unique properties of nanodiamonds. By replacing some carbon atoms with nitrogen atoms, researchers create “nitrogen vacancies” within the diamond structure. These vacancies serve as quantum sensors that become activated in the presence of a microwave field. When these engineered nanodiamonds are illuminated by a laser while suspended in tiny droplets of liquid, they emit light. The intensity of this emitted light is directly influenced by the surrounding chemical environment, allowing scientists to discern whether specific substances are present nearby.

The implications of this discovery are vast, particularly in fields where detecting minuscule quantities of chemicals is crucial. Traditional methods of chemical analysis often require substantial sample sizes and lengthy processes, but Ajoy’s innovative approach allows for the analysis of trace amounts. The droplets utilized in this technique are significantly smaller than a raindrop, providing a means to study individual cells or trace chemicals efficiently. The sensitivity and speed of this technique offer researchers a powerful tool for advancing our understanding of complex chemical environments.

Remarkably, the cost-efficiency of this method is another aspect that sets it apart from existing technologies. With the capacity to analyze hundreds of thousands of droplets for a mere 63 cents worth of diamond dust, researchers can undertake extensive chemical analyses without the exorbitant expenses typically associated with such precision instruments. This economical nature may facilitate its adoption across various scientific disciplines, democratizing access to advanced detection methodologies.

Beyond initial applications, the technique holds promise for expansive real-world implementations. One of the key areas of interest involves the detection of paramagnetic ions, substances that can be exceedingly difficult to study with traditional analytical techniques. In preliminary experiments, the research team demonstrated the capability to detect trace levels of gadolinium ions and TEMPOL—a stable radical molecule associated with oxygen sensitivity. These findings exemplify the potential to analyze short-lived reactive oxygen species, which play pivotal roles in cellular metabolism, aging, and stress response.

As the scientific community continues to prioritize precision and speed in chemical detection, Ajoy and his colleagues are keenly aware of the broader applications of their findings. They are exploring methodologies to attach specific identification components such as antibodies to the nanodiamonds, augmenting the tool’s capabilities for biological investigations. Imagine wielding this technology to create diagnostic tests that can identify viral infections even when present in scant quantities—an invaluable asset in contemporary public health initiatives.

Further, Ajoy envisions a future where this technology could contribute to environmental monitoring. In a world increasingly concerned with pollutant tracking, a portable system powered by nanodiamond microdroplets could allow for real-time assessments of air and water quality. Such a system could be deployed in various settings—from laboratories to remote or industrial sites—broadening the scope of research and monitoring activities significantly.

Looking towards revolutionary applications, the research team aims to explore the integration of their findings into self-driving bioreactors. These advanced systems, designed to cultivate microorganisms for medicine, biofuels, or food production, could benefit substantially from the heightened level of control afforded by the quantum sensors embedded within individual droplets. Each nanodiamond-laden droplet acts as a miniature beaker, potentially housing a single cell, thereby facilitating real-time monitoring of micro-organisms’ health and productivity.

In this regard, the research offers a glimpse into the future of bioprocessing, where precise, localized measurements offered by the droplet approach could lead to innovation in the biopharmaceutical industry. For instance, the ability to monitor process conditions in harsh environments—be they terrestrial or extraterrestrial—opens doors for sustainable food production and resource generation in settings previously considered unviable.

The implications of this research extend beyond immediate scientific endeavors; they intersect with critical challenges facing humanity. With the potential to enhance the detection of contaminants or pathogens, this technology could inform responses to global health crises, addressing threats before they escalate. Thus, this pioneering work doesn’t just reflect a technical achievement; it also embodies a profound commitment to leveraging science to solve pressing, real-world problems.

As the research landscape continues to evolve, it becomes increasingly evident that interdisciplinary collaboration is essential. The successful fusion of expertise from diverse fields—including chemistry, biology, and microfluidics—highlights the importance of teamwork in achieving ambitious scientific objectives. The current study was made possible through the Laboratory-Directed Research and Development (LDRD) program at Berkeley Lab, fostering innovation and encouraging bold experimentation among researchers.

As efforts intensify to refine the technologies and methodologies around this approach, the scientific community remains hopeful that future developments will unlock even more applications for nanodiamond-based quantum sensors. With far-reaching implications for diagnostics, environmental monitoring, and bioprocessing, the journey toward harnessing quantum properties for practical applications has only just begun, illuminating a path where science may not only observe but understand and intervene in the complexities of our world.

In summary, the integration of nanodiamonds in microdroplets represents a transformative breakthrough in chemical detection. The marriage of quantum sensing with practical applications marks a leap forward in our ability to study the microscopic world. As researchers continue their work, the potential to unravel complex chemical interactions and enhance our detection capabilities heralds a new dawn in scientific and technological progress.

Subject of Research: Nanodiamonds in Microdroplets for Quantum Sensing

Article Title: Revolutionizing Chemical Detection: Quantum Sensors Powered by Nanodiamonds in Microdroplets

News Publication Date: TBD

Web References: TBD

References: TBD

Image Credits: Ajoy Lab/UC Berkeley

Keywords: Quantum sensing, nanodiamonds, chemical detection, paramagnetic species, microfluidics, bioprocessing, disease diagnostics, environmental monitoring, reactive oxygen species, interdisciplinary research, innovation.