An integrated photonic millimeter-wave receiver with sub-ambient noise

Decades of progress in radiofrequency (RF) transistors and receiver frontends have profoundly impacted wireless communications, remote sensing, navigation, and instrumentation. Growing demands for data throughput in 6G networks, timing precision in positioning systems, and resolution in atmospheric sensing and automotive radar have pushed receiver frontends into the millimeter-wave (mmW) and sub-mmW/THz regimes. At these frequencies, however, the noise performance of field-effect transistors (FETs) degrades rapidly due to parasitic effects, limited carrier mobility, hot electrons, and shot noise. Parametric transducers that couple electromagnetic signals to optical fields offer quantum-limited sensitivity at room temperature. Electro-optic materials enable receivers that convert RF signals into optical phase shifts. While early demonstrations used resonant devices and recent efforts have focused on cryogenic microwave-to-optical quantum transduction, room-temperature electro-optic receivers have yet to achieve noise figures comparable to their electronic counterparts. Here we demonstrate a room-temperature integrated cavity electro-optic mmW receiver on a lithium tantalate (LiTaO3) photonic integrated circuit with 2.5% on-chip photon-number transduction efficiency, achieving 250 K noise temperature at 59.33 GHz--matching state-of-the-art LNAs. We report the first direct resolution of thermal noise in cavity electro-optic transduction, showing the system is fundamentally limited by thermal photon occupation (~100) in the mmW cavity. Our work establishes integrated photonics as a path to surpass electronic LNAs while offering exceptional resilience to strong electromagnetic inputs and immunity to EMI, establishing cavity electro-optics as a low-noise, chip-scale, EMI-resilient receiver frontend for mmW applications and scalable analog processing in the optical domain.