Maximal Quantum Fisher Information for Mixed States
Maximal Quantum Fisher Information for Mixed States
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DOI：
10.1103/physrevlett.123.250502
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发表时间：
2019-12-18
影响因子：
8.6
通讯作者：
Braun, Daniel
中科院分区：
文献类型：
--
作者：
Fiderer, Lukas J.;Fraisse, Julien M. E.;Braun, Daniel
我们研究幺正动力学的量子计量学。给出了从任意混合态出发的最优幺正态制备和相应的最优测量精度的解析解。这是一个严格的推广已知的最佳初始状态和测量精度上界的结果，只能饱和，如果纯状态。特别是，我们提供了一个概括的混合状态的测量精度的上限随时间变化的哈密顿量，可以饱和的最佳哈密顿控制。这些结果精确地揭示了混合态在量子计量学中的全部潜力。
We study quantum metrology for unitary dynamics. Analytic solutions are given for both the optimal unitary state preparation starting from an arbitrary mixed state and the corresponding optimal measurement precision. This represents a rigorous generalization of known results for optimal initial states and upper bounds on measurement precision which can only be saturated if pure states are available. In particular, we provide a generalization to mixed states of an upper bound on measurement precision for time-dependent Hamiltonians that can be saturated with optimal Hamiltonian control. These results make precise and reveal the full potential of mixed states for quantum metrology.