Transient behaviors of photon switching by quantum interference

We have experimentally studied the transient behaviors of photon switching by quantum interference in laser-cooled ⁸⁷Rb atoms. The experimental results are consistent with theoretical predictions. We show that the rise time of the probe absorption cannot be less than 2∕Γ where Γ is the spontaneous decay rate of the excited states. In the low-intensity limit, the rise time is equal to 2Γ∕(Ω_c²+Ω_s²) for the scheme used here, where Ω_c and Ω_s are the Rabi frequencies of the coupling and switching fields. A simple picture based on the dark and nondark states is provided to explain these transient behaviors.