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arXiv · 1811.05598

Entanglement estimation in non-optimal qubit states

Stefano Scali·Roberto Franzosi
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Abstract

In the last years, a relationship has been established between the quantum Fisher information (QFI) and quantum entanglement. In the case of two-qubit systems, all pure entangled states can be made useful for sub-shot-noise interferometry while their QFI meets a necessary and sufficient condition [1]. In M-qubit systems, the QFI provides just a sufficient condition in the task of detecting the degree of entanglement of a generic state [2]. In our work, we show analytically that, for a large class of one-parameter non-optimal two-qubit states, the maximally entangled states are associated with stationary points of the QFI, as a function of such parameter. We show, via numerical simulations, that this scenario is maintained for the generalisation of this class of states to a generic M-qubit system. Furthermore, we suggest a scheme for an interferometer able to detect the entanglement in a large class of two-spin states.

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Stefano Scali, Roberto Franzosi. 2019-11-06. Entanglement estimation in non-optimal qubit states. https://doi.org/10.1016/j.aop.2019.167995

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