Low light level all-optical switching in a four-level atom-cavity system

• An all-optical switching in a four-level atom-cavity system.
• In this system, an extra coherence between two ground states is induced by two coupling lasers.
• This results that we can use one weak field to control another weak field at low light levels.

We report on an all-optical switching in a double ∧ four-level atom-cavity system both theoretically and experimentally. In this system, an extra coherence between two ground states is induced by two coupling lasers, thus the loss of the cavity field decreases. Then, we can use one weak field to control another weak field at low light levels. Compared to the three-level atom-cavity system, the power of the switching laser can be much weaker in the four-level atom-cavity system.