Tunable transient evolutional behaviours of a four-level atomic vapour and the application to photonic logic gates

The evolutional optical behaviours (turn-on dynamics) of a four-level N-configuration atomic system are considered based on the transient solution to the equations of motion of atomic probability amplitudes. It is shown that the quantum interference between the signal and control fields can lead to the controllable absorption and transparency properties of the atomic vapour. One of the most remarkable properties of the present scheme is that the absorption (or transmittance) of the probe light in the atomic vapour depends on the intensity ratio of the signal field to the control field, and thus the tunable optical features (transparency or opaqueness to the probe light) can be realized by tuning the quantum interferences between the signal and control fields. The present mechanism can be applicable to designs of some new photonic and quantum optical devices such as logic and functional devices as well as optical switches. Two typical photonic logic gates (NOT and NOR gates) designed based on the tunable four-level optical responses are presented as illustrative examples.