Atomic-candle techniques beyond the small-signal regime

Applying a phase-modulated AC magnetic signal at a frequency near the hyperfine splitting of an atom forces the steady-state population to oscillate at integer harmonics of the modulation frequency. Resonance behaviour of the first two harmonics near the Rabi frequency, known as $\alpha$ and $\beta$ Rabi resonances, is widely used for microwave field magnetometry and as a power standard, known as the atomic candle. Unlike in previous work, here we explore the Rabi resonances beyond the small-signal approximation using computer simulation and report experimental observations of higher harmonics in cold $^{87}$Rb atoms. This will allow us to relax the small-signal assumption and possibly exploit the higher-order harmonics in order to improve precision of magnetometers and power standards based on the atomic candle technique.