Experimental Sensitivity Enhancement of a Quantum Rydberg Atom-Based RF Receiver with a Metamaterial GRIN Lens. - Anton Tishchenko; Demos Serghiou; Ashwin Thelappilly Joy; Paul Marsh; Paul Martin 018; Tim W. C. Brown; Gabriele Gradoni; Mohsen Khalily; Rahim Tafazolli (CoRR, 2025)