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

2008/11/29 by Holger F. Hofmann
Computer Science · Physics and Astronomy · #Mechanical and Optical Resonators #Orbital Angular Momentum in Optics #Quantum Information and Cryptography #quant-ph

paper · pdf · doi:10.1103/physreva.79.033822

published as Phys. Rev. A 79, 033822 (2009) · 4 pages, no figures

arxiv created 2008/11/29 · openalex publication_date 2009/03/16 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

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.

Citations

• Quantum enhancement ofN-photon phase sensitivity by interferometric addition of down-converted photon pairs to weak coherent light
• Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement
• Mach-Zehnder Interferometry at the Heisenberg Limit with Coherent and Squeezed-Vacuum Light