We address the characterization of qubit chains and assess the performances of local measurements compared to those provided by Feynman probes, i.e., nonlocal measurements realized by coupling a single-qubit register to the chain. We show that local measurements are suitable to estimate small values of the coupling and that a Bayesian strategy may be successfully exploited to achieve optimal precision. For larger values of the coupling Bayesian local strategies do not lead to a consistent estimate. In this regime, Feynman probes may be exploited to build a consistent Bayesian estimator that saturates the Cramér-Rao bound, thus providing an effective characterization of the chain. Finally, we show that ultimate bounds to precision, i.e., saturation of the quantum Cramér-Rao bound, may be achieved by a two-step scheme employing Feynman probes followed by local measurements.

Characterization of qubit chains by Feynman probes / D. Tamascelli, C. Benedetti, S. Olivares, M.G.A. Paris. - In: PHYSICAL REVIEW A. - ISSN 2469-9926. - 94:4(2016 Oct 26).

Characterization of qubit chains by Feynman probes

D. Tamascelli;C. Benedetti;S. Olivares;M.G.A. Paris
2016

Abstract

We address the characterization of qubit chains and assess the performances of local measurements compared to those provided by Feynman probes, i.e., nonlocal measurements realized by coupling a single-qubit register to the chain. We show that local measurements are suitable to estimate small values of the coupling and that a Bayesian strategy may be successfully exploited to achieve optimal precision. For larger values of the coupling Bayesian local strategies do not lead to a consistent estimate. In this regime, Feynman probes may be exploited to build a consistent Bayesian estimator that saturates the Cramér-Rao bound, thus providing an effective characterization of the chain. Finally, we show that ultimate bounds to precision, i.e., saturation of the quantum Cramér-Rao bound, may be achieved by a two-step scheme employing Feynman probes followed by local measurements.
Feynman probes; quantum estimation; quantum measurement
Settore FIS/03 - Fisica della Materia
Quantum Probes for Complex Systems
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/448647
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