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arXiv · 2607.23978

Non-Hermitian-enhanced quantum sensing in an optical interferometer

X. J. Huang·Lei Xiao·Bingzi Huo·X. X. Yi·Peng Xue
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Abstract

The precision of quantum parameter estimation is traditionally constrained by the quantum Cramér-Rao bound, which is based on the Hermitian measurement framework. Recent studies of non-Hermitian systems have suggested new possibilities for enhancing parameter-estimation sensitivity. Here, we experimentally realize quantum parameter estimation using a non-Hermitian observable on a linear optical platform. The parameter is encoded in single-photon probe states and read out with a Sagnac interferometer, which allows us to reconstruct the complex expectation value of the implemented non-Hermitian observable from interference fringes. We observe a reduced error-propagation variance compared with the optimal Hermitian observable for the same probe-state model. This advantage remains visible under amplitude-damping noise. We further analyze the complete optical measurement as a physical positive-operator-valued measure (POVM) and show, through the corresponding classical Fisher information (CFI), that the observed non-Hermitian advantage is consistent with the standard quantum metrological limit when all output ports are included. Our results provide an experimental route to non-Hermitian observable readout and clarify its operational meaning in quantum sensing.

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X. J. Huang, Lei Xiao, Bingzi Huo, X. X. Yi, Peng Xue. 2026-07-27. Non-Hermitian-enhanced quantum sensing in an optical interferometer. https://arxiv.org/abs/2607.23978

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