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中国物理学会期刊

基于量子Fisher信息测量的实验多体纠缠刻画

CSTR: 32037.14.aps.72.20230356

Experimentally characterizing multiparticle entanglement based on measuring quantum Fisher information

CSTR: 32037.14.aps.72.20230356
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  • 量子Fisher信息在量子度量与量子信息领域的研究中至关重要, 然而在实验中的提取却十分棘手, 尤其是对于大尺度的量子系统. 这里我们发展了利用测量量子态间重叠的方式来高效提取量子Fisher信息的方法, 对于纯态而言, 这种方法只需要在量子系统中引入一个额外的辅助比特并施加单次测量即可实现. 相对于以往的量子Fisher信息提取方法, 需要更少由测量带来的时间资源消耗, 因此高效且具有扩展性. 我们将这种方法应用于经历量子相变的三体相互作用系统中多体纠缠的刻画, 并使用核磁共振量子模拟器实验展示了该方案的可行性.

     

    Quantum Fisher information plays a vital role in the field of quantum metrology and quantum information, because it not only quantifies the ultimate precision bound of parameter estimation but also provides criteria for entanglement detection. Nevertheless, experimentally extracting quantum Fisher information is intractable. Quantum state tomography is a typical approach to obtaining the complete information about a quantum system and extract quantum Fisher information. However it becomes infeasible for large-scale quantum systems owing to the exponentially growing complexity. In this paper, we present a general relationship between quantum Fisher information and the overlap of quantum states. Specifically, we show that for pure states, the quantum Fisher information can be exactly extracted from the overlap, whereas for mixed states, only the lower bound can be obtained. We also develop a protocol for measuring the overlap of quantum states, which only requires one additional auxiliary qubit and a single measurement for pure state. Our protocol is more efficient and scalable than previous approaches because it requires less time and fewer measurements. We use this protocol to characterize the multiparticle entanglement in a three-body interaction system undergoing adiabatic quantum phase transition, and experimentally demonstrate its feasibility for the first time in a nuclear magnetic resonance quantum system. We conduct our experiment on a 4-qubit nuclear magnetic resonance quantum simulator, three of which are used to simulate the quantum phase transition in a three-body interaction system, and the remaining one is used as the auxiliary qubit to detect the overlap of the quantum state. We use gradient ascent pulse engineering pulses to implement the process of evolution. By measuring the auxiliary qubit, the experimental results of quantum Fisher information are obtained and match well with the theoretical predictions, thus successfully characterizing the multiparticle entanglement in a practical quantum system. We further confirm our results by performing quantum state tomography on some quantum states in the adiabatic process. The experimentally reconstructed quantum states are close to the corresponding instantaneous ground states.

     

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