  Rydberg atoms, with one highly-excited, nearly-ionized electron, have extreme
sensitivity to electric fields, including microwave fields ranging from 100 MHz
to over 1 THz. Here we show that room-temperature Rydberg atoms can be used as
sensitive, high bandwidth, microwave communication antennas. We demonstrate
near photon-shot-noise limited readout of data encoded in amplitude-modulated
17 GHz microwaves, using an electromagnetically-induced-transparency (EIT)
probing scheme. We measure a photon-shot-noise limited channel capacity of up
to 8.2 Mbit/s and implement an 8-state phase-shift-keying digital communication
protocol. The bandwidth of the EIT probing scheme is found to be limited by the
available coupling laser power and the natural linewidth of the rubidium D2
transition. We discuss how atomic communications receivers offer several
opportunities to surpass the capabilities of classical antennas.
