Quantum Shot Noise Limit in a Rydberg RF Receiver Compared to Thermal Noise Limit in a Conventional Receiver

Electromagnetically induced transparency in a vapor of Rydberg atoms can be used for radio frequency (RF) electric field sensing. Such sensors can be traceable, tunable, compact, and electrically passive. One application for these electric field sensors is as a receiver for RF communications, converting a 5G transmission in free space to a modulated optical signal in a fixed network. Different figures of merit are used for an electric-field sensor and a 5G receiver; so it is not straightforward to determine under which operating conditions a Rydberg RF receiver may outperform a conventional antenna and receiver. Here, we consider two fundamental limiting sources of noise, calculating the quantum shot noise limit in a Rydberg RF receiver and comparing this to the thermal noise limit in a conventional macroscopic receiver. For a typical experimental setup, we show that the quantum shot noise can only fall below the thermal noise floor when the symbol rate is below 1-2 MSymbol/s. Higher order signal modulation will be needed to further increase data rate whilst using this constrained symbol rate to limit the fundamental noise floor.