Quantum channel-estimation with particle loss: GHZ versus W states
  We consider quantum channel-estimation for depolarizing channels and phase-flip channels extended by ancilla qubits and fed with a GHZ or W state. After application of the channel one or several qubits can be lost, and we calculate the impact of the loss on the quantum Fisher information that determines the smallest uncertainty with which the parameters of these channels can be estimated. 
Julien Mathieu Elias Fra\"isse and Daniel Braun
quant-ph