Coherent and Squeezed Vacuum Light Interferometry: Parity detection hits the Heisenberg limit

TL;DR

This paper demonstrates that combining coherent and squeezed vacuum light in an interferometer with parity detection achieves phase sensitivity at the Heisenberg limit, surpassing classical limits and matching quantum bounds.

Contribution

It shows that parity detection in a coherent-squeezed vacuum interferometer reaches the Heisenberg limit, providing a detailed comparison with alternative detection schemes.

Findings

Phase sensitivity saturates the quantum Cramer-Rao bound.

Heisenberg-limit sensitivity achieved with equal mixing of coherent and squeezed vacuum.

Parity detection outperforms or matches other detection methods in this scheme.

Abstract

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.