Quantum interferometry with and without an external phase reference
  We discuss the role of an external phase reference in quantum interferometry. We point out inconsistencies in the literature with regard to the use of the quantum Fisher information (QFI) in phase estimation interferometric schemes. We discuss the interferometric schemes with and without an external phase reference and show a proper way to use QFI in both situations. 
Marcin Jarzyna and Rafal Demkowicz-Dobrzanski
quant-ph