Generalized Coherent States and Extremal Positive Operator Valued   Measures
  We present a correspondence between positive operator valued measures (POVMs) and sets of generalized coherent states. Positive operator valued measures describe quantum observables and, similarly to quantum states, also quantum observables can be mixed. We show how the formalism of generalized coherent states leads to a useful characterization of extremal POVMs. We prove that covariant phase space observables related to squeezed states are extremal, while the ones related to number states are not extremal. 
Teiko Heinosaari and Juha-Pekka Pellonp\"a\"a
quant-ph math-ph math.MP