Quantum Metrology with Indefinite Causal Order.

  title={Quantum Metrology with Indefinite Causal Order.},
  author={Xiaobin Zhao and Yuxiang Yang and Giulio Chiribella},
  journal={Physical review letters},
  volume={124 19},
We address the study of quantum metrology enhanced by indefinite causal order, demonstrating a quadratic advantage in the estimation of the product of two average displacements in a continuous variable system. We prove that no setup where the displacements are used in a fixed order can have root-mean-square error vanishing faster than the Heisenberg limit 1/N, where N is the number of displacements contributing to the average. In stark contrast, we show that a setup that probes the… Expand

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