  We analyze the interactions of particle detectors with coherent states of a
free scalar field. We find that the eigenvalues of the post-interaction 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.
