All path-symmetric pure states achieve their maximal phase sensitivity in conventional two-path interferometry

Abstract

It is shown that the condition for achieving the quantum Cramer-Rao bound of phase estimation in conventional two-path interferometers is that the state is symmetric with regard to an (unphysical) exchange of the two paths. Since path symmetry is conserved under phase shifts, the maximal phase sensitivity can be achieved at arbitrary bias phases, indicating that path symmetric states can achieve their quantum Cramer-Rao bound in Bayesian estimates of a completely unknown phase.

4 pages, no figures

References in corpus (3)

• High photon number path entanglement in the interference of spontaneously downconverted photon pairs with coherent laser light
• Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement
• Quantum enhancement of N-photon phase sensitivity by interferometric addition of down-converted photon pairs to weak coherent light