Ambient to Cryogenic High-Frequency Response of Zero-Bias Graphene Photodetectors.

Emerging cryogenic technologies suffer from scaling discrepancies due to limitations stemming from the electrical signal lines connecting the ambient to the cryogenic environment. Currently employed radio frequency cabling offers limited operation bandwidths, therefore requiring large amounts of valuable space and inherently also conducting large amounts of heat. Realizing the ambient-to-cryogenic signal transfer by optical fibers could resolve all of these issues. However, for this purpose, cryogenic-compatible, high-speed, zero-bias-operated photodetectors are required. In this work, we demonstrate a metamaterial-graphene photodetector able to generate high-speed electrical signals in a cryostat without any need for electrical feed lines. This is enabled by a nanostructured metamaterial-graphene architecture that utilizes nanoscale optical hot spots to simultaneously enhance absorption and enable zero-bias carrier extraction. Beyond that, the devices offer high-frequency operations above 100 GHz, a small footprint, and compatibility with various substrates. The signal transfer is further demonstrated by cryogenic optical communication with bit rates of >100 Gbit/s. These results demonstrate a robust platform for high-bandwidth optical-to-electrical conversion, providing a scalable pathway for low-power signal interfacing in next-generation cryogenic systems and quantum technologies.