Feedback control plays a crucial role in preparation and manipulation of quantum states, to evolve the quantum system towards a desired result. Here we report a novel feedback control system utilizing two four-wave mixing (FWM) processes, in which the first FWM process functions as an amplifier while the second FWM process serves as an active nonlinear controller. We experimentally investigate the classical properties of the output states, and demonstrate the manipulation of quantum states through the active nonlinear controller. Remarkably, we observe that the quantum correlation of the quantum states can be efficiently controlled and enhanced, even when the amplifier operates at a significantly low level of pump power. Furthermore, we identify an optimal intensity gain for the active nonlinear controller, which maximizes the quantum correlation of the system. These findings present a new strategy employing an active controller to enhance quantum correlation, which holds the potential to improve the communication fidelity of quantum information processing and enhance the measurement precision of quantum metrology in future applications.

中文翻译：

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热铷蒸气主动非线性反馈控制的实验实现


反馈控制在量子态的准备和操纵中起着至关重要的作用，以使量子系统朝着期望的结果发展。在这里，我们报告了一种利用两个四波混频（FWM）过程的新型反馈控制系统，其中第一个 FWM 过程充当放大器，而第二个 FWM 过程充当有源非线性控制器。我们通过实验研究了输出态的经典特性，并演示了通过主动非线性控制器对量子态的操纵。值得注意的是，我们观察到，即使放大器在泵浦功率极低的情况下工作，量子态的量子相关性也可以得到有效控制和增强。此外，我们确定了有源非线性控制器的最佳强度增益，这最大化了系统的量子相关性。这些发现提出了一种采用有源控制器来增强量子相关性的新策略，有可能提高量子信息处理的通信保真度并提高未来应用中量子计量的测量精度。