All coherent field states entangle equally

We analyze the interactions of particle detectors with coherent states of a free scalar field. We find that the eigenvalues of the postinteraction density matrices of i) a single detector, ii) two detectors, and iii) the partial transpose of the latter, are all independent of which coherent state the field was in. A consequence of these results is that a detector pair can harvest the same amount of entanglement from any coherent field state as from the vacuum.