Researchers at UC Santa Barbara have identified a novel and robust qubit within silicon, potentially accelerating the development of practical quantum technologies. The newly discovered CN center, composed of carbon and nitrogen atoms, offers a compelling alternative to the currently studied T center, which suffers from instability due to its hydrogen component. This finding addresses a critical challenge in quantum device manufacturing—the need for physical systems with desirable quantum properties that are also easily reproducible. “Unlike the T center, this defect does not contain hydrogen and will, therefore, be more robust and easier to realize in actual devices,” explained Kevin Nangoi, a postdoctoral scholar in the Computational Materials Group who led the project. Identifying a stable, telecom-wavelength light emitter in silicon represents a significant advance toward scalable quantum technologies.
CN Center Defects as Robust Silicon Qubits
The pursuit of stable qubits within silicon has yielded a promising candidate: the CN center, a defect composed of carbon and nitrogen atoms, offering a potential solution to long-standing challenges in quantum device fabrication. Unlike previously studied silicon defects, the CN center’s composition avoids the inclusion of hydrogen, a factor that has historically compromised the reliability of quantum systems. Researchers at UC Santa Barbara have demonstrated through computational modeling that this structural difference translates to increased robustness, a critical attribute for scalable quantum technologies. The team, led by postdoctoral scholar Kevin Nangoi in professor Chris Van de Walle’s Computational Materials Group, utilized first-principles simulations to predict the properties of this novel qubit. These simulations are vital, allowing researchers to explore materials before physical realization, and guide the engineering of new devices.
The T center, while capable of storing quantum information for extended periods and emitting telecom-wavelength light, suffers from fragility due to the presence of hydrogen, which readily moves within the silicon crystal and complicates manufacturing processes. Crucially, the CN center not only mirrors the desirable electronic and optical characteristics of the T center—specifically, its ability to emit light in the telecom range—but also exhibits superior structural stability. Mark Turiansky, a group alumnus now at the U.S.
Naval Research Laboratory, affirmed, “Our results show that the CN center reproduces the key electronic and optical properties that render the T center attractive for quantum applications; in particular, the center is structurally stable and produces light in the telecom range.” Van de Walle anticipates that experimental confirmation of these findings could accelerate the development of advanced quantum technologies, leveraging the existing infrastructure of silicon-based electronics, stating, “If confirmed experimentally, the CN center could serve as a practical new building block for quantum devices, potentially accelerating the development of advanced quantum technologies [while] using the same silicon material that powers today’s electronics.”
First-Principles Simulations Predict Telecom-Band Emission
While the NV center in diamond remains a prominent qubit candidate, attention has shifted to silicon-based defects offering comparable performance alongside manufacturing advantages. The T center, a silicon defect emitting light at telecom wavelengths crucial for long-distance quantum communication, recently emerged as a promising option, exhibiting long quantum coherence times. However, its composition—carbon and hydrogen—introduced significant fabrication hurdles due to hydrogen’s inherent instability within the silicon crystal lattice and tendency to migrate during processing. Researchers employed advanced first-principles computer simulations to model the CN center’s behavior at the atomic level, a technique enabling the exploration of material properties before physical realization. These simulations are vital for proactively assessing the viability of new materials and guiding future device engineering efforts. Naval Research Laboratory. This hydrogen-free design addresses a critical limitation of the T center, potentially streamlining manufacturing processes and enhancing device reliability, ultimately accelerating the development of scalable quantum technologies utilizing the ubiquitous silicon platform.
If confirmed experimentally, the CN center could serve as a practical new building block for quantum devices, potentially accelerating the development of advanced quantum technologies [while] using the same silicon material that powers today’s electronics.
T Center Fragility Drives CN Center Research
The team’s work, recently published in Physical Review B, centers on identifying robust quantum building blocks within silicon, leveraging the existing infrastructure of the semiconductor industry. While the T center can effectively store quantum information for durations comparable to the well-studied NV center in diamond and emits light within the crucial telecom band, its reliance on hydrogen presents significant manufacturing challenges. “Hydrogen can easily move within the crystal and is difficult to control during processing, making reproducible and reliable device manufacturing more challenging to achieve,” explained Kevin Nangoi, a postdoctoral scholar who spearheaded the project. These simulations are crucial for accelerating materials discovery and guiding fabrication efforts. Naval Research Laboratory. The absence of hydrogen in the CN center’s structure is the key to its anticipated robustness and ease of integration into future quantum devices. The team believes this characteristic addresses a critical obstacle in scaling up quantum technology.
Our results show that the CN center reproduces the key electronic and optical properties that render the T center attractive for quantum applications; in particular, the center is structurally stable and produces light in the telecom range.
