In the ever-evolving landscape of quantum sensing, nitrogen vacancy (NV) centers in diamond continue to occupy a cornerstone position due to their exceptional ability to probe magnetic fields with nanoscale precision. These atomic-scale defects, comprising a nitrogen atom adjacent to a vacancy in the diamond lattice, have been predominantly harnessed as single-qubit sensors. Traditional single-qubit NV sensors excel at measuring both static and fluctuating magnetic fields at nanometric distances, elucidating material properties and biological phenomena with remarkable spatial resolution. However, recent breakthroughs now push this frontier forward, exploiting multi-qubit architectures formed by pairs of NV centers and nearby nuclear spins to unlock new sensing capabilities.
The team led by Rovny, Kolkowitz, and de Leon has unveiled pioneering protocols that leverage entanglement and multi-qubit control to measure correlated noise and complex spatiotemporal magnetic fluctuations at previously inaccessible length scales. Their work confronts a fundamental limitation of single-qubit sensors: the inability to directly capture nonlocal correlators and the challenges in disambiguating signal correlations from noise variance. By moving to multi-qubit configurations, they open doors to refined magnetometry approaches where entanglement itself becomes a resource for enhanced sensitivity and direct correlation readout.
For NV centers that do not interact strongly and remain spectrally unresolved due to their nanoscale proximity, the researchers devised a sophisticated phase-cycling protocol. This method exploits a third qubit, a nearby ^13C nuclear spin, coupled coherently to the NV centers. The nuclear spin serves as a coherent control tool, enabling selective single-NV spin flips pivotal for phase cycling—effectively disentangling magnetic correlations from variance-induced fluctuations in the sensor signals. Crucially, this technique works even for NV centers aligned along the same crystallographic axis, where spectral resolution is insufficient to distinguish them individually, expanding the operational regime of multi-qubit sensing.
Venturing into length scales on the order of 10 nanometers, the study harnesses the inherent dipole–dipole interactions between two NV centers to prepare maximally entangled Bell states. This leap to entangled-state sensing marks a paradigm shift by enabling direct measurement of magnetic field correlations rather than inferring them through combining separate, single-qubit measurements. The approach alters the sensitivity scaling with readout noise from a quadratic to a linear regime, which is highly consequential. For NV center readout fidelity typical in current experimental setups—where noise exceeds the quantum projection limit by roughly 30-fold—this shift translates into over an order of magnitude gain in measurement sensitivity.
Importantly, the ability to create and control entangled states in such solid-state systems carries profound implications for nanoscale metrology. Unlike classical sensors, entangled NV pairs can jointly respond to correlated magnetic fluctuations in their environment, offering unparalleled access to the spatial structure and temporal dynamics of nanoscale magnetic noise. This capability could revolutionize the probing of condensed matter phenomena, molecular dynamics, and biomagnetic processes at scales relevant to quantum information science, materials engineering, and life sciences.
Beyond the proof of principle, the authors demonstrate concrete experimental strategies to detect high-resolution correlators with pairs of strongly interacting NV centers. These methods build on controlled dipolar coupling and coherent manipulation sequences that disentangle intricate noise patterns with sub-10-nanometer spatial resolution. The strong interactions effectively mediate access to multi-qubit entangled states, further elevating the precision and scope of quantum sensing methodologies.
This work also addresses a key practical bottleneck of NV-based sensing: the off-resonant readout technique traditionally used to measure NV spin states introduces substantial noise, hampering the ultimate sensitivity. The entanglement-based protocol’s linear readout-noise scaling counters this limitation decisively, presenting a viable pathway for deploying multi-qubit quantum sensors in real-world environments where noise is unavoidable and readout fidelity remains a challenge.
Moreover, the integrated use of ^13C nuclear spins as auxiliary qubits reflects an elegant synergy between different quantum degrees of freedom inherent in diamond’s lattice. Nuclear spins serve as stable, coherent control elements with long intrinsic coherence times, complementing the fast manipulation capabilities of electron-spin qubits. This hybrid system facilitates robust implementations of error-resistant phase cycling and quantum logic operations critical to advanced nanoscale sensing tasks.
The implications of this advance reverberate across multiple disciplines. From probing long-range magnetic correlations in novel quantum materials to enhancing the sensitivity of nanoscale magnetic resonance imaging (nano-MRI), the ability to access multi-qubit correlations substantially widens the functional landscape of quantum sensors. It paves the way for investigations where spatially and temporally correlated noise sources can be characterized and controlled with exceptional accuracy, unlocking new paradigms in metrology, sensing, and quantum technology development.
Looking ahead, integrating such entanglement-enabled sensing platforms with scalable quantum networks could enable distributed sensing architectures capable of mapping magnetic phenomena across larger length scales and complex environments. Additionally, refining the protocols to incorporate error-corrected entangled states and leveraging advanced readout schemes could further push sensitivity limits and robustness in practical applications.
In essence, the work by Rovny, Kolkowitz, and de Leon heralds a transformative era in diamond-based quantum sensing, moving beyond the confines of single-qubit paradigms to exploit entanglement and multi-qubit control as fundamental resources. This leap not only amplifies intrinsic sensitivity but also enriches the information content extractable from the quantum environment surrounding NV centers. As these protocols and experimental techniques mature, they stand poised to redefine the frontiers of nanoscale magnetometry and quantum sensor technology.
Their results underscore how quantum entanglement, historically a hallmark of quantum information science, is now becoming a critical asset in precision measurement science. The ability to harness multi-qubit quantum states within solid-state platforms opens vast opportunities for sensing and characterizing magnetic fields with a precision and nuance unimaginable with classical approaches. This convergence of quantum control and nanoscale sensing epitomizes a rapidly advancing synergy at the intersection of quantum physics and applied metrology.
In summation, this landmark research highlights a transformative approach where entanglement serves as both a metaphorical and literal resource, enabling quantum sensors to peer deeper and more clearly into the microscopic magnetic world. Multi-qubit quantum sensors with entangled NV centers are no longer a theoretical aspiration but a realized platform demonstrating marked sensitivity and functionality gains. This progress is expected to catalyze breakthroughs in nanoscale characterization across physics, chemistry, and biology, ushering a new epoch in quantum-enabled sensing technologies.
Subject of Research: Multi-qubit nanoscale sensing with entanglement in NV centers in diamond
Article Title: Multi-qubit nanoscale sensing with entanglement as a resource
Article References:
Rovny, J., Kolkowitz, S. & de Leon, N.P. Multi-qubit nanoscale sensing with entanglement as a resource. Nature 647, 876–882 (2025). https://doi.org/10.1038/s41586-025-09760-y
Image Credits: AI Generated
DOI: 10.1038/s41586-025-09760-y
Keywords: Nitrogen vacancy centers, quantum sensing, entanglement-enhanced metrology, dipole–dipole coupling, phase cycling, quantum magnetometry, nuclear spin control, nanoscale magnetic noise, quantum information, diamond quantum sensors
