Phase sensitivity at the Heisenberg limit in an SU(1,1) interferometer   via parity detection
  We theoretically investigate the phase sensitivity with parity detection on an SU(1,1) interferometer with a coherent state combined with a squeezed vacuum state. This interferometer is formed with two parametric amplifiers for beam splitting and recombination instead of beam splitters. We show that the sensitivity of estimation phase approaches Heisenberg limit and give the corresponding optimal condition. Moreover, we derive the quantum Cram\'er-Rao bound of the SU(1,1) interferometer. 
Dong Li, Bryan T. Gard, Yang Gao, Chun-Hua Yuan, Weiping Zhang, Hwang   Lee, and Jonathan P. Dowling
quant-ph