This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers have developed and demonstrated a new hybrid photonic platform that integrates quantum emitters with photonic devices, providing a way to reliably control the interaction between photons and quantum information carriers. The chip-based platform, which combines gallium phosphide (GaP) with a diamond substrate, could help make quantum networks more practical by providing a way to connect quantum devices over long distances.
Scaling up quantum technology to create communication networks requires connecting quantum memories, or qubits, over long distances. Although fiber-optic networks offer a promising way to do this using optical signals, a key challenge is reliably converting information stored in qubits into optical photons that can travel through the network. "We show that our hybrid-integrated GaP-on-diamond nanophotonic platform can address this challenge by realizing reliably controlled interactions between photons and a type of qubit called a silicon-vacancy (SiV) center in diamond," said the paper's first author, Nicholas S.
Yama from the University of Washington. "GaP also has strong nonlinear properties that enable optical frequency conversion, switching and modulation, all of which are needed for networking applications." In the journal Optica Quantum, researchers led by Kai-Mei C. Fu from Washington University and Pacific Northwest National Laboratory describe their new hybrid platform, including a scalable fabrication process they developed to address a longstanding challenge in producing diamond-based photonic devices.
They used this process to fabricate more than 600 GaP nanophotonic cavities on a diamond substrate with a 99.5% yield. "If GaP-on-diamond proves to be a viable path forward, it could be among the most straightforward paths to realizing quantum networks at scale for practical applications such as secure communications and cryptography," said Yama. "The same technology could also support broader quantum computing applications, while the ability to create quantum systems spanning large distances could open up possibilities well beyond networking." GaP-on-diamond has been studied for more than a decade as a potential scalable platform for diamond-based qubits.
However, getting the photonic devices and SiV centers to interact strongly enough to reliably control the qubits has proven difficult. This requires a regime known as high cooperativity, in which the interaction is strong enough to produce deterministic behavior. "Until now, it has been difficult to achieve high cooperativity with GaP-on-diamond because the GaP photonic layer was spatially separated from the SiV centers in the diamond," said Yama.
"Early devices used partial etching of the diamond to mitigate this, but because this process is nonstandard, it is difficult to scale up using established fabrication methods." In 2023, Fu's group showed that they could fabricate GaP-on-diamond devices without modifying the diamond by using a scalable stamp-transfer process. However, the optical interactions were not strong enough for practical use. In the new work, they went back to the drawing board and redesigned the structure to improve the performance while also perfecting the fabrication process.
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