The development of quantum technologies has become one of the most dynamic and promising frontiers in modern science. This pursuit begins with a deep understanding of the strange and counterintuitive principles that govern the quantum world, and how those laws can be harnessed to create real, useful systems. At the University of California, Santa Barbara (UCSB), physicist Ania Jayich, the Bruker Endowed Chair in Science and Engineering, the Elings Chair in Quantum Science, and co-director of the NSF Quantum Foundry, is leading pioneering work in this area. Her laboratory specializes in using laboratory-grown diamond as the primary material to explore and manipulate quantum phenomena at the atomic scale.
Jayich’s research sits at the intersection of quantum physics and materials science, focusing on how atomic-scale imperfections in diamonds—known as spin qubits—can be engineered for advanced quantum sensing applications. Among the remarkable researchers in her group, Lillian Hughes has made a significant breakthrough in this field. Having recently completed her Ph.D. at UCSB and moving on to Caltech for postdoctoral research, Hughes co-authored three major papers in 2025—one in PRX and two in Nature—that demonstrated, for the first time, that not only individual qubits but two-dimensional ensembles of many quantum defects can be organized and entangled within diamond. This achievement represents a critical step toward developing solid-state quantum systems that can deliver measurable quantum advantages in sensing, marking a new chapter in the design of quantum devices.
Engineering the Quantum Defects
The Jayich Lab has developed a method to create configurations of nitrogen-vacancy (NV) centers—atomic-scale defects in diamond where a nitrogen atom substitutes for a carbon atom adjacent to a vacant site. These NV centers serve as stable, controllable quantum systems. According to Hughes, the team can engineer these defects with remarkable precision, controlling their density and dimensionality to form dense, depth-confined two-dimensional (2D) layers. By adjusting how the defects are oriented within the diamond lattice, the researchers can induce non-zero dipolar interactions between them—a crucial condition for achieving quantum entanglement among multiple spins.
In her PRX study titled “A strongly interacting, two-dimensional, dipolar spin ensemble in (111)-oriented diamond,” Hughes and her collaborators demonstrated that the engineered 2D NV ensembles exhibit strong spin–spin coupling. This interaction allows the system to go beyond individual qubit operations, opening a pathway to collective quantum phenomena that could significantly enhance sensing precision and sensitivity.
An NV center’s unique properties arise from the quantum mechanical concept of spin, which in this case can remain coherent for exceptionally long times, even at room temperature. These long-lived spin states make NV centers especially valuable for quantum sensing applications. The spins couple directly to external magnetic fields, enabling researchers to detect and map magnetic signals at the nanoscale.
From MRI to Quantum Sensing
The idea of using spin as a sensor is not new—it underlies magnetic resonance imaging (MRI), a technique developed in the 1970s that revolutionized medical diagnostics. MRI works by aligning the spins of protons in a magnetic field and detecting the radiofrequency signals they emit as they return to their lower-energy states. Jayich and her team are now extending this concept into the quantum regime, where control over spin states can achieve unprecedented sensitivity.
What sets Jayich’s group apart is their ability to create strongly interacting spin ensembles in solid-state materials. Previous quantum sensing experiments using NV centers typically relied on isolated spins or collections of non-interacting spins. By contrast, Hughes’s dense, interacting 2D NV arrays allow researchers to exploit collective quantum effects, such as entanglement, to surpass classical measurement limits. This quantum advantage manifests as improved signal-to-noise ratios, which translates directly into greater precision in measurements of weak magnetic or electric fields.
Why Diamond is Ideal for Quantum Sensors
Although entanglement-assisted sensing had been demonstrated before, those experiments were confined to gas-phase atomic systems, such as those used in atomic clocks and GPS. However, integrating these sensors into compact, scalable devices has proven challenging. Diamond-based quantum sensors, by contrast, offer a solid-state platform that can be easily miniaturized and brought into close proximity with the system being studied.
Gas-phase atomic sensors require complex infrastructure—vacuum chambers, lasers, and magnetic traps—that limit their applicability to nanoscale measurements. In contrast, NV centers in diamond are robust, stable, and can operate at room temperature, making them ideal for studying systems at the nanometer scale, such as biological molecules or thin-film electronic materials. Jayich emphasizes that this proximity advantage is a major reason why diamond-based sensors are so exciting—they can integrate seamlessly with various target materials, from superconductors to proteins, enabling quantum-level insight into their structure and behavior.
Probing Materials and Biology at the Quantum Level
The potential applications of these diamond quantum sensors are vast. They can be used to probe electronic, magnetic, and biological systems with nanometer precision. For instance, nuclear magnetic resonance (NMR)—a cornerstone technique in chemistry and biology—relies on detecting the tiny magnetic fields produced by atomic nuclei. By applying NV-based quantum sensing, researchers could achieve similar insights but at a scale thousands of times smaller, enabling real-time imaging of individual molecules or nanoscale materials.
Such sensors could also shed light on superconducting or magnetic materials, helping researchers understand the quantum phenomena that govern their properties. This capability has implications for developing next-generation quantum computers, energy-efficient materials, and nanotechnology-based medical diagnostics.
Overcoming Quantum Noise and Enhancing Precision
Every measurement in physics faces the challenge of noise, which sets a limit on precision. In quantum systems, quantum projection noise defines the so-called standard quantum limit (SQL)—a boundary that cannot be surpassed using unentangled sensors. To break this limit, scientists must induce correlations among quantum states, a process known as spin squeezing.
Jayich explains this concept using an analogy: if your measuring stick has centimeter-spaced markings, you cannot use it to measure a microscopic organism like an amoeba. Spin squeezing effectively reduces the “spacing” of those markings by correlating quantum states, thereby reducing uncertainty and enabling finer measurements. This quantum noise reduction is one of the key innovations driving the UCSB group’s research.
Amplifying Quantum Signals
Beyond squeezing, the team’s second Nature paper explored another groundbreaking approach—signal amplification. Instead of reducing noise, this method amplifies the signal itself, enhancing detectability without adding extra noise. Returning to the measuring-stick analogy, signal amplification makes the amoeba appear larger, making it easier to measure with existing tools.
By combining these two strategies—noise reduction and signal amplification—Jayich’s team is pushing the frontier of quantum metrology, a field that aims to redefine the limits of precision measurement.
Looking Ahead: From Laboratory to Real-World Systems
Jayich remains optimistic about the future of diamond-based quantum sensors. She believes that the remaining challenges are primarily technical rather than fundamental. Future work will focus on improving the control and positioning of NV centers within the diamond lattice to create regular arrays of spins. Achieving such ordered structures would enable even stronger entanglement and more robust signal enhancement, paving the way toward practical quantum advantage in real-world sensing applications.
A key challenge lies in the materials engineering—controlling where and how spins are incorporated into the diamond lattice. Current techniques result in somewhat random placement, but Jayich’s team is developing new growth methods to produce precisely patterned spin grids, ensuring optimal spacing and interaction strength.
Conclusion
The work being done at UCSB’s Quantum Foundry exemplifies the synergy between quantum physics, materials science, and engineering innovation. By mastering the art of creating and manipulating quantum defects in diamond, Jayich and her collaborators are not only expanding the boundaries of fundamental physics but also laying the foundation for practical technologies that could revolutionize sensing, imaging, and computation.
From spin squeezing to signal amplification, their research demonstrates how the subtle interplay of quantum mechanics can be harnessed to produce tangible benefits—making measurements more precise, sensors more sensitive, and the invisible quantum world increasingly accessible to human understanding.
Story Source: University of California - Santa Barbara.
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