Dual-frequency operation in a single atomic magnetometer and frequency-shift keying modulation of magnetic field communication

We present a dual-frequency operation technique for a radio-frequency atomic magnetometer utilizing a single natural-abundance rubidium (Rb) vapor cell for the first time, and demonstrate a proof-of-concept for magnetic field communication using binary frequency-shift keying (BFSK) under unshielded conditions. The two operational frequencies correspond to the Larmor frequencies of ⁸⁵Rb and ⁸⁷Rb, as determined by their distinct gyromagnetic ratios in the same magnetic field environment. A rate of 400 symbols/s is adeptly demonstrated with an ambient noise floor of < 20 pT/√Hz, attaining a signal-to-noise ratio of 20 dB. These findings highlight the efficacy of dual-frequency atomic magnetometry as a sophisticated and resilient technique for magnetic field communication in unshielded environments.