Acta Physica Sinica, Volume. 68, Issue 23, 234203-1(2019)

Analysis of entanglement source based on coherent feedback control

Yao-Yao Zhou1、*, Peng-Fei Li1, Zhi-Hui Yan2,3, and Xiao-Jun Jia2,3
Author Affiliations
  • 1Department of Physics, Taiyuan Normal University, Jinzhong 030619, China
  • 2State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
  • 3Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
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    Entangled state of light with quantum correlations between amplitude and phase quadratures is a necessary quantum resource in optical continuous variable (CV) quantum information systems. The CV Einstein-Podolsky-Rosen (EPR) entangled optical field is one of the most basic quantum resources, which can be generated by a non-degenerate optical parametric amplifier (NOPA) operated below the threshold pump power. Manipulating the EPR entangled state of light effectively can break through the limitation of the imperfect performance of optical components in optical cavities and then further improve the entanglement level under certain conditions. So it is necessary to find out an effective optical scheme of manipulating quantum state of light. The non-measurement based coherent feedback control (CFC) system without introducing any extra noise into the controlled system, can be used to stabilize, control and improve the performance of various quantum systems. Only by selecting the right experimental parameters can the CFC system play its positive role in reaching a maximum efficacy. The key optical component, i.e. optical controller in CFC system, greatly affects the final manipulation effects. In 2015, using the method of CFC, our research team experimentally realized the enhancement of entanglement to different levels by changing the optical controller with different transmissivity values for seed optical beams. At the same time, the threshold pump power of the NOPA is reduced to different levels also. Due to the technical reasons, the transmissivity of the optical controller selected in the experiment is almost the same for the signal optical field and idle optical field. In this paper, we emphasize the condition that the transmissivity of the optical controller for the signal optical field is different from that for idle optical field. Firstly, we theoretically study the final effects of manipulating entanglement source by using the coherent feedback optical cavity under the above conditions. It is concluded that if the transmittance of control beam splitter (CBS) is low, the feedback control optical cavity works best when the optical controller has different transmissivity for signal optical beam and idle optical beam, and that if the transmittance of CBS is high, the transmittance of the optical controller for signal optical beam almost equals that for idle optical beam to make the feedback control optical cavity work best. Then we theoretically investigate the dependence of the quantum correlation noise of the quadrature amplitude and quadrature phase of the output optical fields from CFC-NOPA system on other physical parameters. Combining with the actual experimental conditions, we can find the optimal transmissivity of the optical controller and appropriate range of frequency to optimize the effects of CFC, which provides the basis for correctly selecting the actual experimental parameters in CFC systems. Theoretical analysis results also show that with the higher input and output coupling efficiency and higher nonlinear conversion efficiency of NOPA, the entangled state of light with higher entanglement degree can be obtained experimentally. This provides the reference for obtaining better quantum resources needed for studying the CV quantum information.


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    Yao-Yao Zhou, Peng-Fei Li, Zhi-Hui Yan, Xiao-Jun Jia. Analysis of entanglement source based on coherent feedback control[J]. Acta Physica Sinica, 2019, 68(23): 234203-1

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    Paper Information

    Received: Jul. 30, 2019

    Accepted: --

    Published Online: Sep. 17, 2020

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