Optimal measurements in phase estimation: simple examples

Year: 2016

Authors: Wasak T., Smerzi A., Pezzè L., Chwedenczuk J.

Autors Affiliation: Univ Warsaw, Inst Theoret Phys, Ul Pasteura 5, PL-02093 Warsaw, Poland;‎ INO CNR, QSTAR, Largo Enrico Fermi 2, I-50125 Florence, Italy;‎ LENS, Largo Enrico Fermi 2, I-50125 Florence, Italy

Abstract: We identify optimal measurement strategies for phase estimation in different scenarios in which the interferometer acts on two-mode symmetric states. For pure states of a single qubit, we show that optimal measurements form a broad set parametrized with a continuous variable. When the state is mixed, this set reduces to merely two possible measurements. For two-qubit symmetric Werner state, we find the optimal measurement and show that estimation from the population imbalance is optimal only if the state is pure. We also determine the optimal measurements for a wide class of symmetric N-qubit Werner-like states. Finally, for a pure symmetric state of N qubits, we find under which conditions the estimation from the full N-body correlation and from the population imbalance is optimal.


Volume: 15 (5)      Pages from: 2231  to: 2252

KeyWords: Estimation theory; Quantum interferometry; Optimal measurements; Entanglement
DOI: 10.1007/s11128-016-1248-5

Citations: 8
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