2015/09/30 by Florian Fröwis, Pavel Sekatski, Wolfgang Dür · 5 citations
Computer Science · Mathematics · Physics and Astronomy · #Mathematical analysis #Mathematics #Metrology #Multipartite #Multipartite entanglement #Observable #Physics #Protocol (science) #Quantum #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum and electron transport phenomena #Quantum discord #Quantum entanglement #Quantum mechanics #Quantum metrology #Quantum state #Squashed entanglement #Statistical physics #Unitary state #Upper and lower bounds #Weak measurement #quant-ph
paper · pdf · doi:10.1103/physrevlett.116.090801
published as Phys. Rev. Lett. 116, 090801 (2016) · 5 pages, 3 figures; v2: improved presentation, close to published version
openalex publication_date 2016/03/03 · arxiv created 2016/03/11 · arxiv updated 2016/03/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We propose an experimentally accessible scheme to determine the lower bounds on the quantum Fisher information (QFI), which ascertains multipartite entanglement or usefulness for quantum metrology. The scheme is based on comparing the measurement statistics of a state before and after a small unitary rotation. We argue that, in general, the limited resolution of collective observables prevents the detection of large QFI. This can be overcome by performing an additional operation prior to the measurement. We illustrate the power of this protocol for present-day spin-squeezing experiments, where the same operation used for the preparation of the initial spin-squeezed state improves also the measurement precision and hence the lower bound on the QFI by 2 orders of magnitude. We also establish a connection to the Leggett-Garg inequalities. We show how to simulate a variant of the inequalities with our protocol and demonstrate that large QFI is necessary for their violation with coarse-grained detectors.