Entanglement estimation in non-optimal qubit states

Year: 2019

Authors: Scali S., Franzosi R.

Autors Affiliation: DSFTA, University of Siena, Via Roma 56, 53100 Siena, Italy; Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom; Department of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, United Kingdom; STAR & CNR – Istituto Nazionale di Ottica, Largo Enrico Fermi 2, I-50125 Firenze, ItalyFirenze, Italy, Italy

Abstract: In the case of two qubits, all pure entangled states can be made useful for sub-shot-noise interfer- ometry [1]. However, with non-optimal two-qubit states, the value of quantum Fisher information provides just a sufficient condition in the task of detecting the degree of entanglement of a generic state. 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 quantum Fisher infor- mation, as a function of such parameter. We show, via numerical simulations, that this scenario is maintained for the generalization of this class of states to a generic M-qubits system. Furthermore, we suggest a scheme for an interferometer able to detect the entanglement in a large class of two-spin states.


Volume: 411      Pages from: 167995-1  to: 167995-11

More Information: We are grateful to A. Smerzi, M. Gessner, M. Gabbrielli and L. Pezze for useful discussions. R. F. thanks the support by the QuantERA project “Q-Clocks” and the European Commission.
KeyWords: Fisher information, Qubit state, Quantum Information
DOI: 10.1016/j.aop.2019.167995

Citations: 3
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