In the relentless pursuit of practical quantum technologies, one of the grand challenges lies in understanding and manipulating the fundamental quantum phenomena underpinning material behavior. At the forefront of this endeavor is the laboratory of Ania Jayich, a distinguished figure holding the Bruker Endowed Chair in Science and Engineering and co-director of UC Santa Barbara’s National Science Foundation Quantum Foundry. Their material platform of choice is laboratory-grown diamond, a solid-state crystal host to quantum defects known as nitrogen-vacancy (NV) centers, which are emerging as prime candidates for quantum sensing applications due to their exceptional spin properties.
Jayich’s group operates at the nexus of quantum physics and materials science, leveraging atomic-scale engineering to fabricate tailored arrays of NV centers within diamond. The hallmark achievement of their recent research, spearheaded by Dr. Lillian Hughes during her doctoral studies, is the creation and entanglement of two-dimensional ensembles of NV spin qubits. This work represents a paradigm shift from prior efforts focused solely on single qubits or uncorrelated ensembles, navigating instead towards crafting strongly interacting, depth-confined, planar layers of spins. Such intricate control over both the spatial configuration and dipolar interactions among these spins has been detailed across a trio of influential papers — one published in PRX and two in Nature — underscoring a critical advancement in realizing metrological quantum advantages in solid-state systems.
The NV center in diamond is a point defect comprising a substitutional nitrogen atom adjacent to a carbon vacancy. This defect forms a unique quantum system: a spin-1 electronic ground state with remarkable coherence times, even at room temperature. The spin’s long-lived nature provides an exquisite handle for magnetic field sensing through spin-dependent photoluminescence, enabling highly sensitive detection of nanoscale magnetic environments. Jayich emphasizes that by engineering the nitrogen-vacancy centers with precise control over their density and crystallographic orientation—specifically within a (111)-oriented diamond lattice—the team induces robust dipolar interactions between spins. These interactions are essential for fostering collective quantum behavior, a prerequisite for entanglement-enhanced sensing protocols.
Traditional quantum sensing experiments have relied on ensembles of non-interacting spins, which offer sensitivity scaling limited by the standard quantum limit. Hughes’s innovation lies in overcoming this constraint by fabricating dense, two-dimensional spin ensembles where dipolar couplings create correlated spin states. In effect, the system can harness quantum entanglement to surpass classical noise thresholds, bolstering signal-to-noise ratios and thus measurement precision. This approach mirrors early breakthroughs in gas-phase atomic systems, where entanglement-assisted metrology has been demonstrated. However, Jayich highlights the unique benefits of a solid-state platform: diamond sensors are compact, integrate easily with diverse sample environments, and operate without the extensive laser and vacuum infrastructure atomic sensors require.
From a practical perspective, NV-based quantum sensors can be engineered to reside mere nanometers beneath the diamond surface, enabling their direct proximity to target analytes—be they biological molecules or novel electronic materials. This nano-scale vantage point positions them to probe magnetic phenomena with unprecedented spatial resolution. Jayich’s team envisions applications spanning the elucidation of electronic and superconducting phases to the sensitive detection of nuclear magnetic resonance (NMR) signals from biological samples, where conventional techniques lack spatial or sensitivity resolution. The blend of material science innovation and quantum control in diamond lays a promising foundation for transformative sensing technologies.
A central quantum metrological tool realized in this system is spin squeezing—a process that redistributes quantum noise, diminishing uncertainty in one spin component at the expense of another. Conceptually, squeezing refines the granularity of measurement “rulers,” analogously shrinking the least count of a meter stick to enable the detection of minuscule signals otherwise lost amid quantum projection noise. This noise, inherent to quantum measurements, traditionally limits sensitivity to the standard quantum limit scaling inversely with the square root of the number of sensors. The Jayich lab’s ability to engineer strong spin-spin interactions permits the generation of these crucial squeezed states, paving the way for measurements that exceed classical bounds.
Beyond squeezing, the research investigates signal amplification mechanisms that improve sensitivity by increasing the effective signal strength without a concomitant rise in noise. This feat, described in the subsequent Nature publications, creates a complementary route to enhance metrology: rather than compressing measurement noise, the signal itself is made more distinguishable. Together, squeezing and amplification form a powerful duo in the toolkit for approaching and surpassing the quantum-enhanced measurement frontier. These dual strategies showcase how engineered spin ensembles in diamond can be finely tuned to optimize different facets of quantum advantage.
Despite the groundbreaking results, the pursuit of scalable, practical quantum sensors faces materials challenges. One prominent hurdle is the intrinsic randomness in the placement of NV centers during diamond growth, which currently precludes the formation of perfectly ordered spin arrays. Such disorder limits the ultimate precision and controllability of spin interactions. Jayich’s team is actively addressing this by refining fabrication techniques to position spins on well-defined grids within the 2D plane, which would enable more uniform and tunable coupling strengths. Achieving this architectural control is anticipated to unlock the next tier of quantum advantage in sensing experiments.
Looking forward, the team envisions integrating these engineered diamond spin layers into compact devices capable of high-precision sensing in complex environments. The solid-state nature of the platform inherently facilitates interfacing with samples, scalability, and robustness against environmental perturbations. Moreover, the insights garnered into collective spin physics and entanglement dynamics have broader implications, potentially influencing quantum information processing and the development of novel quantum materials. Jayich’s lab is thus not only pushing sensor technology but also expanding the fundamental toolbox available for quantum engineering.
In summary, the recent work from the Jayich group marks a pivotal advance in quantum sensing technology. By transitioning from isolated qubits to engineered, interacting 2D spin ensembles embedded within diamond, they establish a new paradigm where metrological quantum advantage becomes feasible in a robust, solid-state material. This synergy of quantum physics, precise material fabrication, and fundamental metrology promises to accelerate the realization of practical quantum devices with impactful applications across science and technology.
Subject of Research: Engineering of two-dimensional spin qubit ensembles in diamond for quantum-enhanced sensing
Article Title: Demonstration of Strongly Interacting Two-Dimensional Dipolar Spin Ensembles in Diamond Enabling Metrological Quantum Advantage
News Publication Date: October 2025
Web References:
- PRX paper: https://arxiv.org/abs/2503.14585
- First Nature paper: https://www.nature.com/articles/s41586-025-09452-7
- Second Nature paper: https://www.nature.com/articles/s41586-025-09524-8
Image Credits: Brian Long
Keywords: Quantum computing, Qubits, Nitrogen-vacancy centers, Quantum sensing, Spin squeezing, Metrological quantum advantage, Diamond quantum sensors, Dipolar spin interactions
