Quantum-Based Broadband Integrated Sensing and Communication with Rydberg Atomic Receiver

Integrated sensing and communications (ISAC) demands front-ends that natively support coherent data reception and accurate environmental awareness within a single hardware chain. We present a quantum ISAC receiver that replaces the conventional RF antenna-mixer-LNA cascade with a centimeterscale Rydberg-atom vapor cell, enabling quantum-traceable RF-to-optical I/Q downconversion. Using electromagnetically induced transparency (EIT) and Autler-Townes (AT) physics, the receiver provides a phase-accurate baseband suitable for standard coherent communications, while reusing the same front-end for range sensing via pilot-aided stepped tones. A hybrid tuning strategy - coarse laser-controlled state hopping with fine AC-Stark compensation - realizes non-uniform stepped coverage across 2.6-3.6 GHz. A compact prototype demonstrates centimeter-level range sensing (RMSE = 1.06 cm within 1.6-1.9 m) and resolves 15 cm separations in controlled sparse cases, while preserving stable phase tracking required by coherent demodulation. These results indicate a practical pathway to compact, calibration-free ISAC nodes with simplified RF hardware, where communications pilots can be opportunistically reused for accurate sensing.