Researchers are tackling the challenge of scaling up spin-based quantum sensors, which hold promise for advances in fields from materials science to biomedicine. M. Reefaz Rahman, Karsten Schnier, and Ryan Goldsmith, all from the Department of Electrical and Computer Engineering at The University of Alabama, alongside Benjamin J. Lawrie from Oak Ridge National Laboratory, Joseph M. Lukens from Purdue University, and Seongsin M. Kim from The University of Alabama and Seongsin M., demonstrate a novel approach using photonic links to deliver microwave control signals to these sensors. This work is significant because it overcomes limitations of traditional microwave delivery , namely thermal noise and design constraints , by utilising fibre optics, paving the way for quieter, more scalable and thermally isolated quantum sensing systems and potentially distributed quantum networks.
Remote RF Control of NV Centres via Fibre
Scientists have recently demonstrated a novel framework for remotely controlling Spin qubits using radio frequency (RF) signals transmitted via optical fiber, achieving a significant step towards scalable quantum technologies. This approach circumvents the constraints of traditional coaxial cables, which struggle to deliver high-frequency signals efficiently in cryogenic and high-magnetic-field environments. The ability to distribute control signals via optical fiber opens possibilities for creating interconnected quantum nodes and scaling up quantum sensing and computing architectures. The team’s work builds upon the growing interest in optically accessible spin qubits, like NV centers in diamond and boron vacancies in hexagonal boron nitride, which are increasingly utilized as components in quantum sensors, qubits, and quantum memories.
By addressing the microwave delivery bottleneck, this innovation unlocks opportunities for coherently addressing spins in challenging environments, paving the way for advanced spin-based quantum sensing applications. Furthermore, the RFoF system offers advantages for high-field cryogenic experiments, where conventional microwave delivery becomes increasingly difficult as spin transition frequencies reach the sub-THz range0.2 Tesla, scaling these efforts to cryogenic temperatures presents significant technical hurdles. This new approach provides a viable solution, enabling coherent spin control even at high magnetic fields and low temperatures. The recovered RF tone from the photodiode output was routed to a broadband microstrip “pinhole” antenna, fabricated on a 1.6mm thick FR-4 substrate with a copper top layer and metallic ground plane. The team positioned the diamond sample above the antenna aperture to maximize coupling to the NV spin transitions, verifying antenna response by measuring the reflection coefficient (S11), which confirmed broadband coupling in the 2.8, 3.0GHz range.
To characterize the RFoF link, scientists reported optical-to-RF power conversion efficiency based on optical power incident on the photodiode and the recovered RF power delivered to the antenna0.7 dBm. This breakthrough delivers a scalable pathway toward high-field (multi-10GHz to sub-THz), cryogenic, and networked-node operation for spin-based quantum systems0.2% at higher delivered power. The authors acknowledge limitations in recovered RF power and link linearity, but suggest improvements through enhanced modulation depth and optimised photodiode operation.