Quantum technologies stand on the brink of revolutionizing numerous sectors, from computing and communication to advanced sensing applications. At the heart of these transformative technologies lie qubits— the fundamental units of quantum information. Quantum bits derive their extraordinary power from the principles of superposition and entanglement, enabling computational capabilities orders of magnitude beyond classical counterparts. The realization of practical quantum devices demands not only qubits that exhibit exceptional coherence and controllability but also scalability and manufacturability within existing materials platforms. Silicon, the cornerstone of contemporary electronics, naturally emerges as an optimal candidate, promising integration with the mature semiconductor industry infrastructure. Yet, identifying suitable quantum defects or centers within silicon that can robustly function as qubits remains a pivotal challenge.
In a recent breakthrough spearheaded by researchers from the University of California, Santa Barbara under the leadership of Professor Chris Van de Walle, a novel silicon-based qubit platform has been theoretically revealed. This new defect center, known as the carbon-nitrogen (CN) complex, offers compelling advantages over previously studied centers. The findings are detailed in a forthcoming publication in the prestigious journal Physical Review B, marking a significant advancement in the quest for silicon-compatible quantum emitters. The research leverages high-fidelity first-principles computational methods to elucidate the atomic-scale structure and quantum properties of the CN center, providing a roadmap for experimental realization.
Defect centers in crystals have a celebrated history in quantum science, notably the nitrogen-vacancy (NV) center in diamond which serves as an archetypal solid-state qubit. NV centers enable coherent electron spin manipulation alongside the emission of single photons, facilitating applications in quantum sensing and communication. The paradigm extended to silicon has incorporated the so-called T center, a defect formed by carbon and hydrogen atoms. The T center stands out for its ability to emit light in the telecom wavelength band, crucial for fiber-optic quantum communication, and for demonstrating long spin coherence times competitive with NV centers. However, the inclusion of hydrogen atoms inherently injects instability, given hydrogen’s mobility and sensitivity during semiconductor fabrication processes, thereby complicating reproducibility and device scalability.
Addressing this crucial limitation, the CN center replaces hydrogen with nitrogen, thereby forming a more structurally stable and chemically robust defect complex within the silicon lattice. According to lead postdoctoral researcher Kevin Nangoi, the absence of hydrogen means that the CN center is less susceptible to the migration and diffusion phenomena that plague hydrogen-containing defects. This stability enhances its viability as a reliable quantum emitter for device integration, overcoming a major hurdle in silicon-based quantum photonics. The team’s computational exploration confirms that the CN center preserves essential electronic and optical characteristics akin to the T center, producing photon emission precisely within the technologically vital telecom window.
The research utilized state-of-the-art ab initio simulations based on density functional theory (DFT) combined with many-body perturbation techniques to capture the defect’s electronic structure and excited-state properties. Such computational tools empower scientists to predict material behavior from first principles—without recourse to prior experimental data—thus accelerating discovery by guiding synthetic strategies. Mark Turiansky, a former member of the group now affiliated with the U.S. Naval Research Laboratory, emphasized the significance of the CN center’s structural resilience and telecom emission profile, underscoring its suitability for quantum information processing and photonic network devices.
The implications of identifying a hydrogen-free quantum-light emitter embedded in silicon stretch far beyond academic curiosity. By leveraging silicon’s well-established fabrication ecosystems, the CN center could catalyze the development of scalable quantum communication infrastructure, quantum repeaters, and integrated quantum photonic circuits. Unlike diamond or other exotic materials, silicon’s compatibility with existing CMOS processes holds the promise of mass production and functional quantum devices seamlessly integrated with classical electronics. This synergy is critical for achieving practical quantum advantage and transitioning quantum systems from laboratory curiosities to commercial technologies.
Moreover, the telecom wavelength emission characteristic of the CN center is particularly advantageous. Telecom bands experience minimal attenuation in optical fibers, enabling photons to travel long distances with negligible loss—a prerequisite for building quantum networks spanning metropolitan, continental, or even global scales. The CN center’s ability to generate such photons on-demand within a stable and controllable silicon matrix addresses a long-standing bottleneck in realizing fiber-based quantum communication systems, potentially reshaping secure communication paradigms.
Beyond communication, the CN center’s coherent spin states coupled with its optical addressability position it as a versatile qubit candidate for quantum sensing. Precision measurements of magnetic and electric fields, temperature, and strain at the nanoscale utilize the quantum coherence properties of defect centers to surpass classical sensor limits. The enhanced stability imparted by nitrogen substitution could ensure consistent performance across diverse environmental conditions and device cycles.
Although the CN center’s theoretical promise is compelling, experimental verification remains a crucial next step. Fabricating and characterizing this defect at atomic precision will require refined doping and annealing protocols, supported by advanced spectroscopy and microscopy techniques. The theoretical predictions serve as a vital compass directing these experimental efforts, optimizing conditions to realize the CN center reproducibly and harness its quantum functionalities effectively in silicon photonic architectures.
This breakthrough research exemplifies the power of integrating computational materials science with quantum technology development, illustrating how predictive modeling can pioneer solutions to long-standing material challenges. Supported by the U.S. Department of Energy’s Office of Basic Energy Sciences through the Co-design Center for Quantum Advantage, and leveraging computational resources at the National Energy Research Scientific Computing Center, this work exemplifies cooperative interdisciplinary innovation.
Looking forward, the realization of the CN defect center in silicon could unlock a host of quantum devices that benefit from both the extraordinary physics of quantum information science and the practical advantages of silicon technology. The potential to accelerate the deployment of quantum communication networks, quantum processors, and quantum sensors harnessing a stable and manufacturable silicon qubit is an inspiring milestone on the path toward the quantum age.
In summary, the identification of the carbon-nitrogen complex as an alternative to the hydrogen-dependent T center in silicon marks a pivotal advance in quantum material research. It blends atomic-scale precision, advanced computational modeling, and strategic materials engineering to push the boundaries of what silicon quantum technology can achieve. This innovation holds promise not only for fundamental quantum science but also for scalable quantum technology ecosystems compatible with today’s semiconductor manufacturing infrastructure, potentially transforming the quantum landscape for decades to come.
Subject of Research: Quantum defect centers in silicon for quantum information technologies
Article Title: Carbon-nitrogen complex as an alternative to the 𝑇 center in Si
News Publication Date: 10-Feb-2026
Web References: [Physical Review B publication DOI: 10.1103/zy5b-fskh]
Keywords: Quantum information, Materials engineering, Quantum computing, Qubits
