  Realization of practical terahertz wireless communications still faces many
challenges. The receiver with high sensitivity is important for THz wireless
communications. Here we demonstrate a terahertz receiver based on the cesium
Rydberg atoms in a room-temperature vapor cell. The minimum detectable THz
electric field is calibrated. With this receiver, the phase-sensitive
conversion of amplitude-modulated or frequency-modulated terahertz waves into
optical signals is performed. The results show that the atomic receiver has
many advantages due to its quantum properties. Especially, the long distance
THz wireless communications is achievable using this receiver. Furthermore, the
atomic receiver can be used in the THz wireless-to-optical link.
