Quantum-enhanced phase estimation with an amplified Bell state

We propose a phase estimation protocol for optical interferometry that employs a probe state (containing on average (n) over bar photons) obtained by squeezing each mode, separately, of a single photon path entangled Bell state. This scheme involves a Mach-Zehnder type interferometer for which each mode is squeezed after the first beam splitter. Information about the differential phase is extracted using a parity detection and the resulting measurement signal is super-resolving and supersensitive, with a minimum phase uncertainty Delta phi = 2/((n) over bar + 1). This probe state can be generated with current technologies where (n) over bar is in the order of many thousands of photons.