Practical quantum metrology with large precision gains in the low photon number regime

TL;DR

This paper demonstrates that using entangled and squeezed states, particularly the squeezed cat-state, can significantly enhance measurement precision in optical quantum metrology at low photon numbers, surpassing classical limits.

Contribution

It introduces a practical quantum state, the squeezed cat-state, showing substantial precision gains and robustness to loss, with a simple measurement scheme that saturates the quantum Fisher information.

Findings

7-fold enhancement in quantum Fisher information over shot noise limit

Squeezed cat-state achieves 3-fold improvement over Gaussian states

Robustness to loss at low photon numbers

Abstract

Quantum metrology exploits quantum correlations to make precise measurements with limited particle numbers. By utilizing inter- and intra- mode correlations in an optical interferometer, we find a state that combines entanglement and squeezing to give a 7-fold enhancement in the quantum Fisher information (QFI) -- a metric related to the precision -- over the shot noise limit, for low photon numbers. Motivated by practicality we then look at the squeezed cat-state, which has recently been made experimentally, and shows further precision gains over the shot noise limit and a 3-fold improvement in the QFI over the optimal Gaussian state. We present a conceptually simple measurement scheme that saturates the QFI, and we demonstrate a robustness to loss for small photon numbers. The squeezed cat-state can therefore give a significant precision enhancement in optical quantum metrology in practical and realistic conditions.