Keywords: 
• 路径纠缠微波 /
• 信号质量 /
• 压缩参量 /
• 纠缠微波光子总数期望值

Abstract: Quantum information theory can improve the performances of the classical information techniques by utilizing the entangled state of electromagnetic field. Path entangled microwave signal distributes its entangled states between spatially separated subsystems of an information system, which can be widely applied to quantum information technology in the future. Currently, there are only several reports on path entangled microwave signal generation. Therefore, the quality of path entangled microwave signal is far from satisfactory. In order to improve the quality of path entangled microwave signal further, we make a discussion about the factors that affect the quality of it and design a quality evaluation scheme for it. Based on the designed quality evaluation scheme, an optimal squeezed parameter selection method is suggested. Firstly, the generation principle of path entangled microwave signal is briefly introduced, and the generated signal is denoted as quantum mechanics operator in the Fock state representation. In the meantime, the qualitative relationship between generated signal and the squeezed parameter is determined. Secondly, a quality evaluation method for path entangled microwave signal is proposed: the quality of generated signal is evaluated by comparing with the expectation value of the entangled microwave photon number which reflects the degree of quantum entanglement. Finally, an approach to selecting the optimal squeezed parameter for generating the path entangled microwave signals is proposed based on the quality evaluation method. The process of it is as follows: an array of squeezed parameters which achieve the highest entanglement probability of different microwave photons is acquired under the premise that the maximal effective number of entangled microwave photons is set to be a certain value. Then an array of expectation values of number of entangled microwave photons corresponding to these squeeze parameters is acquired, and the squeezed parameter corresponding to the largest expectation value is what we are searching for. Through theoretical analysis, we draw a conclusion that the quality of path entangled microwave signal is determined by squeezed parameter. Accurately, it is related to the squeezed degree, but unrelated to the squeezed angle. From simulations, we find that the maximal expectation value of the total number of entangled microwave photons is 3.77 when the simulation proceeds on condition that the maximal number of effective entangled microwave photons is set to be 26. And its corresponding squeezed degree value is 1.77, which means that the optimal path entangled microwave signal can be generated when we set the value of squeezed degree to be 1.77. And our method is proved effective by the simulation results. We provide an original idea on generating high-quality path entangled microwave signals for its experiments and applications.