Correspondence: Enhancing a phase measurement by sequentially probing a   solid state system
  In a recent paper, Liu et al. [Nat. Commun. 6:6726 (2015)] claim to perform the first room temperature entanglement-enhanced phase measurement in a solid-state system. We argue here that this claim is incorrect: their measurement is not enhanced because of the entanglement in their system, but instead the enhancement comes from the fact that the phase shift is applied twice to their state. 
P. A. Knott, W. J. Munro and J. A. Dunningham
quant-ph