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American Physical Society, Physical Review A, 3(93), 2016

DOI: 10.1103/physreva.93.033859

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

Journal article published in 2016 by P. A. Knott, T. J. Proctor, A. J. Hayes, J. P. Cooling, J. A. Dunningham
This paper is available in a repository.
This paper is available in a repository.

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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.