Accessing photon number via an atomic time interval

We show that Rabi resonances can be used to assess field strength in terms of time at the atomic level. Rabi resonances are enhancements in the amplitude of atomic population oscillations when the Rabi frequency, Ω, 'matches' a field-modulation frequency, ωm. We demonstrate that Ω=2κωm and find that κ=1.03±0.05. Since Ω is defined by field strength (i.e., photon number) through atomic constants, and ωm may be referenced to an atomic clock, our work shows that Rabi resonances provide a connection between time and photon number