A usual assumption in quantum estimation is that the unknown parameter labels the possible states of the system, while it influences neither the sample space of outcomes nor the measurement aimed at extracting information on the parameter itself. This assumption is crucial to prove the quantum Cramér-Rao theorem and to introduce the quantum Fisher information as an upper bound to the Fisher information of any possible measurement. However, there are relevant estimation problems where this assumption does not hold and an alternative approach should be developed to find the genuine ultimate bound to precision of quantum measurements. We investigate physical situations where there is an intrinsic dependence of the measurement strategy on the parameter and find that quantum-enhanced measurements may be more precise than previously thought.

Quantum metrology beyond the quantum Cramér-Rao theorem / L. Seveso, M.A.C. Rossi, M.G.A. Paris. - In: PHYSICAL REVIEW A. - ISSN 2469-9926. - 95:1(2017 Jan 10), pp. 012111.012111-1-012111.012111-7. [10.1103/PhysRevA.95.012111]

Quantum metrology beyond the quantum Cramér-Rao theorem

L. Seveso
;
M.A.C. Rossi
;
M.G.A. Paris
2017

Abstract

A usual assumption in quantum estimation is that the unknown parameter labels the possible states of the system, while it influences neither the sample space of outcomes nor the measurement aimed at extracting information on the parameter itself. This assumption is crucial to prove the quantum Cramér-Rao theorem and to introduce the quantum Fisher information as an upper bound to the Fisher information of any possible measurement. However, there are relevant estimation problems where this assumption does not hold and an alternative approach should be developed to find the genuine ultimate bound to precision of quantum measurements. We investigate physical situations where there is an intrinsic dependence of the measurement strategy on the parameter and find that quantum-enhanced measurements may be more precise than previously thought.
geometry
Settore FIS/03 - Fisica della Materia
   Quantum Probes for Complex Systems
   QuProCS
   EUROPEAN COMMISSION
   H2020
   641277
10-gen-2017
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/467386
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