Coherent and Squeezed Vacuum Light Interferometry: Parity detection hits   the Heisenberg limit
  The interference between coherent and squeezed vacuum light can produce path entangled states with very high fidelities. We show that the phase sensitivity of the above interferometric scheme with parity detection saturates the quantum Cramer-Rao bound, which reaches the Heisenberg-limit when the coherent and squeezed vacuum light are mixed in roughly equal proportions. For the same interferometric scheme, we draw a detailed comparison between parity detection and a symmetric-logarithmic-derivative-based detection scheme suggested by Ono and Hofmann. 
Kaushik P. Seshadreesan, Petr M. Anisimov, Hwang Lee, and Jonathan P.   Dowling
quant-ph