# What's the physical interpretation of ρ for dipole forbidden channel?

 P: 4 Consider we have a $\Lambda$ type three level system, the one upper level is denoted by 3, and the two lower levels are denoted by 1 and 2. Assuming that the transitions between 1$\leftrightarrow$3 and 2$\leftrightarrow$3 are dipole alowed, while the transition between two lower states 1 and 2 is dipole forbidden. As we know the real and imaginary part of ρ31 describe the dispersion and absorption of the external light in 1$\leftrightarrow$3 channel. But what does the ρ12 mean?