双端腔Ⅱ类倍频产生四组份纠缠光场

Quadripartite entanglement from two-port resonator with second-order harmonic generation

量子纠缠是执行量子计算和构建量子通信网络的关键资源,制备与操控纠缠态光场是实现量子信息处理的基础要素.本文提出了利用双端光学腔倍频产生四组份纠缠态的理论模型,从耦合波方程出发得到Ⅱ类倍频过程的传输矩阵,通过腔内自再现方程和输入输出传输矩阵理论研究了输出的两束倍频光的噪声特性;对于两束倍频光和两束基频泵浦场,利用多组份纠缠光场的充分必要判据PPT方法(positivity under partial transposition criterion)分析了最小辛本征值与泵浦功率及分析频率之间的关系,研究结果表明基频泵浦光与倍频光之间存在四组份纠缠.

Quantum entanglement is a crucial resource for performing quantum computing and constructing quantum communication networks.The preparation and manipulation of entangled light field are the basic elements of quantum communication.With the development of science and technology,multicolor multipartite entanglement is becoming a kind of special resource for quantum information,quantum networks,and quantum memory.In this paper,we propose a scheme of generating quadripartite entanglement among four output beams from a two-port frequency doubling resonator,in which a type-II phase matching nonlinear crystal is placed.We make two fundamental-frequency pump beams with the same frequency and vertical polarization pass through the nonlinear crystal to produce two frequency-doubling beams.There is a quadripartite entanglement between the frequency-doubling beams,which are output at two ports of the optical resonator,and the incident fundamental beams.Based on the transmission matrix from the coupled wave equation,the self-consistent equations of the intracavity modes and the corresponding noise properties of the output modes can be obtained.Then,the quadripartite entanglement produced from two second harmonic beams and two reflected fundamental-frequency pump beams,is verified by using the positive partial transposition criterion,in a wide range of pumping power and analysis frequency.The setup proposed in this work is compact and experimentally feasible.It is also convenient to separate the four entangled beams spatially,with different wavelengths and polarizations.When the beam wavelengths are matched with 1560 nm(low loss window of fiber)and 780 nm(atomic absorption line of Rb),this scheme can be more useful in both quantum communication and quantum memory.