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The Walker speaks its graph: global and nearly-local probing of the tunnelling amplitude in continuous-time quantum walks. (English) Zbl 1507.82011

Summary: We address continuous-time quantum walks on graphs, and discuss whether and how quantum-limited measurements on the walker may extract information on the tunnelling amplitude between the nodes of the graphs. For a few remarkable families of graphs, we evaluate the ultimate quantum bound to precision, i.e. we compute the quantum Fisher information (QFI), and assess the performances of incomplete measurements, i.e. measurements performed on a subset of the graph’s nodes. We also optimize the QFI over the initial preparation of the walker and find the optimal measurement achieving the ultimate precision in each case. As the topology of the graph is changed, a non-trivial interplay between the connectivity and the achievable precision is uncovered.

MSC:

82B10 Quantum equilibrium statistical mechanics (general)
82B41 Random walks, random surfaces, lattice animals, etc. in equilibrium statistical mechanics
81P45 Quantum information, communication, networks (quantum-theoretic aspects)
81P15 Quantum measurement theory, state operations, state preparations

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