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Scientists achieve precision activation of quantum defects in diamond

A new study led by researchers at the Universities of Oxford, Cambridge and Manchester has achieved a major advance in quantum materials, developing a method to precisely engineer single quantum defects in diamond—an essential step toward scalable quantum technologies. The results have been in the journal Nature Communications.

Using a new two-step fabrication method, the researchers demonstrated for the first time that it is possible to create and monitor, "as they switch on," individual Group-IV quantum defects in diamond—tiny imperfections in the diamond crystal lattice that can store and transmit information using the exotic rules of quantum physics.

By carefully placing single tin atoms into synthetic diamond crystals and then using an ultrafast laser to activate them, the team achieved pinpoint control over where and how these quantum features appear. This level of precision is vital for making practical, large-scale quantum networks capable of ultra-secure communication and distributed quantum computing to tackle currently unsolvable problems.

Study co-author Professor Jason Smith, Department of Materials (University of Oxford) said, "This breakthrough gives us unprecedented control over single tin-vacancy color centers in diamond, a crucial milestone for scalable quantum devices. What excites me most is that we can watch, in real time, how the quantum defects are formed."

Specifically, the defects in the diamond act as spin-photon interfaces, which means they can connect quantum bits of information (stored in the spin of an electron) with particles of light. The tin-vacancy defects belong to a family known as Group-IV color centers—a class of defects in diamond created by atoms such as silicon, germanium, or tin.

Group-IV centers have long been prized for their high degree of symmetry, which gives them stable optical and spin properties, making them ideal for quantum networking applications. It is widely thought that tin-vacancy centers have the best combination of these properties—but until now, reliably placing and activating individual defects was a major challenge.

The researchers used a focused ion beam platform—essentially a tool that acts like an atomic-scale spray can, directing individual tin ions into exact positions within the diamond. This allowed them to implant the tin atoms with nanometer accuracy—far finer than the width of a human hair.

To convert the implanted tin atoms to tin-vacancy color centers, the team then used ultrafast laser pulses in a process called laser annealing. This process gently excites tiny regions of the diamond without damaging it. What made this approach unique was the addition of real-time spectral feedback—monitoring the light coming from the defects during the laser process. This allowed the scientists to see in real time when a quantum defect became active and adjust the laser accordingly, offering an unprecedented level of control over the creation of these delicate quantum systems.

Study co-author Dr. Andreas Thurn (University of Cambridge) said, "What is particularly remarkable about this method is that it enables in-situ control and feedback during the defect creation process. This means we can activate quantum emitters efficiently and with high spatial precision—an important tool for the creation of large-scale quantum networks. Even better, this approach is not limited to diamond; it is a versatile platform that could be adapted to other wide-bandgap materials."

Moreover, the researchers observed and manipulated a previously elusive defect complex, termed "Type II Sn," providing a deeper understanding of defect dynamics and formation pathways in diamond.

Study co-author Professor Richard Curry (University of Manchester) said, "This work unlocks the ability to create quantum objects on demand, using methods that are reproducible and can be scaled up. This is a critical step in being able to deliver quantum devices and allow this technology to be utilized in real-world commercial applications."