Coherent mixed with squeezed vacuum light interferometry: Parity detection hits the Heisenberg limit

Mach-Zehnder interferometry based on mixing the coherent and the squeezed vacuum states of light has Heisenberg limited capabilities for phase estimation. This is so, because the quantum Cramer-Rao bound on sensitivity of phase estimation with the above interferometric scheme reaches the Heisenberg limit when the inputs are mixed in near equal proportions. We show that a detection strategy based on the measurement of parity of photon number in one of the output modes of the interferometer saturates the quantum Cramer-Rao bound of the interferometric scheme, and therefore-as a consequence-hits the Heisenberg limit when the inputs are mixed in equal intensities. © 2012 SPIE