Mainz 2017 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 23: Quantum Information: Concepts and Methods IV
Q 23.2: Talk
Tuesday, March 7, 2017, 14:45–15:00, P 2
Witnessing the metrological efficiency with few expectation values — •Iagoba Apellaniz1, Matthias Keinmann1, Otfried Gühne2, and Géza Tóth1,3,4 — 1Department of Theoretical Physics, University of the Basque Country UPV/EHU, E-48080 Bilbao, Spain — 2Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, 57068 Siegen, Germany — 3IKERBASQUE, Basque Foundation for Science, E-48013 Bilbao, Spain — 4Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, Hungary
In quantum metrology, the precision of parameter estimation plays a central role. For a given quantum state, the quantum Fisher information characterizes the best achievable precision, hence it is very important to obtain it in an experiment. We show how to estimate the quantum Fisher information as a figure of merit of metrological usefulness based on a few expectation values. Our approach is optimal since it gives a tight lower bound on the quantum Fisher information for the given incomplete information. We apply our method to the results of various multi-particle quantum states prepared in experiments with photons, trapped-ions and cold atomic ensembles, such as spin-squeezed states and Dicke states. Based on a few operator expectation values, our approach can also be used for detecting and quantifying entanglement in very large systems.