Researchers from the University of California, Santa Barbara (UCSB) have made significant strides in quantum technology by discovering a novel hydrogen-free silicon defect, termed the CN center. This defect holds promise as a robust qubit capable of emitting telecom-wavelength light, a development that could enhance the scalability of quantum technologies.

The research team, part of Professor Chris Van de Walle’s Computational Materials Group, utilised first-principles computer simulations to uncover the properties of the CN center. This defect mirrors the essential electronic and optical characteristics of the previously studied T center while circumventing the fabrication difficulties associated with hydrogen.

Should experimental validation confirm these findings, the CN center could serve as a structurally stable and manufacturable quantum light emitter in silicon. This advancement would play a crucial role in bridging fundamental quantum research and the practical development of semiconductor-based devices.

The Potential of Quantum Technologies

Quantum technologies are poised to revolutionise fields such as computing, communication, and sensing by leveraging the unique behaviours of matter at the atomic scale. To translate the potential of quantum mechanics into functional devices, it is essential to identify physical systems that exhibit desirable quantum properties while also being amenable to mass production. Silicon, the backbone of contemporary computer chips, emerges as an appealing platform due to its compatibility with the existing trillion-dollar semiconductor industry.

Identifying quantum building blocks, or qubits, within silicon is a vital area of research. In the recent study published in the journal Physical Review B, the researchers focus on defects at the atomic scale that can function as qubits. A well-known example is the NV center in diamond, which consists of a nitrogen atom adjacent to a vacant carbon site. These atomic-scale defects can interact with electrons and light, enabling the emission of single photons for the transmission of quantum information or processing within quantum networks.

Previous research has explored the T center in silicon, which is capable of storing quantum information for extended durations, akin to the NV center. The T center emits light within the telecom band, a wavelength range suitable for low-loss transmission through optical fibres. However, the T center’s reliance on hydrogen renders it susceptible to fabrication challenges; hydrogen atoms can migrate within the crystal, complicating reproducible device manufacturing.

Introducing the CN Center

In their latest study, the UCSB team has identified the CN center as a promising alternative to the T center. Comprising carbon and nitrogen atoms, the CN center does not contain hydrogen, making it potentially more robust and easier to implement in practical devices. Kevin Nangoi, a postdoctoral scholar leading the project, emphasised the advantages of this new defect.

The research team employed sophisticated first-principles computer simulations to model the CN center at an atomic level. Such simulations enable researchers to predict material properties for systems that have yet to be experimentally realised, thus informing future engineering and fabrication efforts.

Mark Turiansky, a group alumnus now a postdoctoral researcher at the U.S. Naval Research Laboratory, remarked on the findings, stating that the CN center replicates the key electronic and optical properties that make the T center appealing for quantum applications. Notably, the CN center is structurally stable and emits light within the telecom range.

Implications for Future Research

Identifying a hydrogen-free quantum light emitter in silicon is a crucial advancement in narrowing the gap between quantum science and scalable technology. Looking ahead, Professor Van de Walle anticipates that, if experimentally validated, the CN center could serve as a foundational building block for future quantum devices. This could significantly accelerate the development of advanced quantum technologies using the same silicon material that powers current electronic devices.

This research received funding from the Department of Energy Office of Science, Office of Basic Energy Sciences, through the Co-design Center for Quantum Advantage (C2QA). The computational work was conducted at the National Energy Research Scientific Computing Center.