# A What is the polarization energy?

1. Oct 21, 2016

I was going through a derivation (equation 4.1.8 in Multi-atomic Coherent Emission by Benedict et al.) and a term called the polarization energy is defined as:

$$\int |\hat{P}(x)|^2 d^3x$$

I have been unable to find much information about this term. In their derivation of the Hamiltonian of an ensemble of atoms, the authors drop this term, but don't exactly explain why (possibly for obvious reason) and I am not entirely sure of its significance. Any ideas?

2. Oct 21, 2016

### Simon Bridge

Generally the energy of something is the amount of work needed to bring the something about.
Context is important though - sometimes something gets a name because it has the right dimensions and involves something else. This integral involves the polarization and has dimensions of energy soo...

Presumably it cannot always be dropped - you need to understand the physics being represented here.
It may just be that they are constructing the hamiltonian for the case where the polarization is weak.