Fig. 3

Demonstration of a directional amplifier with a blue-detuned control field. a Typical measured transmission spectra for the function of the directional amplifier. The solid circles represent T_i→i+1 and the open squares represent T_i+1→i. The incident control power is 5.8 mW, corresponding to C_cw = −3.4. b Transmittance obtained at δ = 0 versus C_cw. The lines in a, b indicate theoretically expected values based on the parameters κ/2π = 16.2 MHz, ω_m/2π = 90.47 MHz, and γ/2π = 22 kHz