物理学报2018，Vol.67Issue(2)：72-78,7.DOI:10.7498/aps.67.20171542
连续变量纠缠态光场在光纤中传输特性的实验研究
Experimental investigation of transmission characteristics of continuous variable entangled state over optical fibers
摘要
Abstract
Continuous variable(CV)quantum entanglement is an essential resource for quantum computation and communi-cation protocols. The use of CV quantum entanglement at a telecommunication wavelength of 1.5 μm in combination with existing fiber telecommunication networks offers the possibility to implement long-distance quantum communica-tion protocols like quantum key distribution(QKD)and applications such as quantum repeaters,quantum teleportation in the future. In spite of the fact that the optical power attenuation of light in a standard telecommunication fiber is lowest at a wavelength of 1.5 μm, the entangled states will interact with fiber channels and the disentanglement will occur. It is one of the important factors restricting the development of long distance quantum information. In this paper, CV entangled state at 1.5 μm telecommunication band is obtained by using a type-II periodically poled KTP (PPKTP)crystal inside a nondegenerate optical parametric amplifier(NOPA).A wedged PPKTP is used for implement-ing frequency-down-conversion of the pump field to generate the optically entangled state and achieving the dispersion compensation between the pump and the subharmonic waves. By controlling the temperature and the length of the PPKTP crystal,a triply resonant optical parametric oscillator with a threshold of 80 mW is realized. Einstein-Podolsky-Rosen (EPR)-entangled beams with quantum correlation of 8.3 dB for both the amplitude and phase quadratures are experimentally generated by using a single NOPA at a pump power of 40 mW and an injected signal power of 10 mW when the relative phase between the pump and injected signal is locked to π. The generated entangled state is coupled into a single-mode optical fiber, and the transmission characteristics of the generated EPR entangled beams through standard single-mode fibers are investigated experimentally and theoretically. A fiber polarization controller is used to compensate for the polarization state variation induced by random fluctuations of birefringence of the single mode fiber when the light propagates along the fiber, and to keep the polarization of light linear at the fiber output. A 0.21 dB quantum entanglement could still be observed for the EPR-entangled beams transmitted through a 50-km-long single-mode fiber. The theoretical prediction considering the excess noise in fiber channel is in good agreement with the experimental result. The generated CV quantum entanglement is highly suitable for the required experiments, such as CV measurement-device-independence QKD based on standard fibers,owing to the fact that the tolerance of the excess noise in the quantum channel can be enhanced significantly with respect to a coherent state if EPR-entangled beams are used.关键词
量子光学/连续变量纠缠态光场/光学参量放大器/光纤信道Key words
quantum optics/continuous variable entangled light/optical parametric amplifier/fiber channel引用本文复制引用
万振菊,冯晋霞,成健,张宽收..连续变量纠缠态光场在光纤中传输特性的实验研究[J].物理学报,2018,67(2):72-78,7.基金项目
国家重点研发计划(批准号:2016YFA0301401)和山西省"1331工程"重点学科建设计划(批准号:1331KS)资助的课题. Project supported by the National Key Research and Develop Program of China (Grant No. 2016YFA0301401) and the Fund for Shanxi“1331 Project”Key Subjects Construction, China (Grant No. 1331KS). （批准号:2016YFA0301401）
