𝒫𝒯 symmetric phase transition and photonic transmission in an optical trimer system.

Parity-time (𝒫𝒯) symmetric structures have exhibited potential applications in developing various robust quantum devices. In an optical trimer with balanced loss and gain, we analytically study the 𝒫𝒯 symmetric phase transition by investigating the spontaneous symmetric breaking. We also illustrate the asymmetric photonic transmission behaviors in both of the 𝒫𝒯 symmetric and 𝒫𝒯 symmetry broken phases. We find (i) the non-periodical dynamics of photonic transmission in the 𝒫𝒯 symmetry broken phase instead of 𝒫𝒯 symmetric phase can be regarded as a signature of phase transition; and (ii) it shows asymmetric photonic transmission behavior in both of the phases but comes from different underlying physical mechanisms. The obtained results may be useful to implement the photonic devices based on coupled-cavity system.