Phase sensitivity via photon-subtraction operations inside Mach-Zehnder interferometer

TL;DR

This paper proposes a quantum metrology scheme using photon-subtraction inside a Mach-Zehnder interferometer with coherent and squeezed vacuum states, demonstrating enhanced phase sensitivity and robustness, even surpassing the Heisenberg limit under certain conditions.

Contribution

It introduces a novel photon-subtraction scheme within a Mach-Zehnder interferometer that improves phase sensitivity and surpasses standard quantum limits, even with losses.

Findings

Photon subtraction enhances phase sensitivity and quantum Fisher information.

Homodyne detection can break the Heisenberg limit.

Scheme remains effective under lossy conditions.

Abstract

Based on the conventional Mach-Zehnder interferometer, we propose a metrological scheme to improve phase sensitivity. In this scheme, we use a coherent state and a squeezed vacuum state as input states, employ multi-photon-subtraction operations and make intensity-detection or homodyne-detection. We study phase sensitivity, quantum Fisher information and quantum Cram\'er-Rao bound under both ideal and lossy conditions. The results indicate that choosing an appropriate detection method and photon subtraction scheme can significantly enhance the phase sensitivity and robustness against photon losses. Even under lossy conditions, the multi-photon subtraction schemes can surpass the standard quantum limit. Notably, the homodyne detection method can even break through the Heisenberg limit. Moreover, increasing the number of photon-subtracted can enhance both phase sensitivity and quantum Fisher information. This research highlights the significant value of this scheme in quantum precision measurement.