Impact of coarse-grained measurement with finite range on continuous-variable quantum key distribution

In continuous-variable quantum key distribution, detectors are necessarily coarse grained and of finite range. We analyze the impact of both features and demonstrate that while coarse graining adds a fixed error to the estimated excess noise, finite range degrades the estimation accuracy of both transmission and excess noise. Moreover, the inaccurate estimation due to finite range may results in secret key rate underestimation, even misjudgment of security. To compensate these consequences, tuning the modulation variance is a possible way.     

The tripartite entanglement in a phase-mismatched frequency non-degenerated optical parametric amplifier

We present an analytical solution for Fokker–Planck equation of phase-mismatched frequency non-degenerated optical parametric amplifier (FNOPA). We investigate the continuous-variable (CV) tripartite entanglement characteristic of FNOPA working at phase-matched and phase-mismatched condition. From below threshold to above threshold, we numerically calculate the dependence of CV tripartite entanglement on relative loss parameter η and phase-mismatched factor Δω. The larger η and the smaller Δω can bring a good entanglement.     

Fock空间中基于波色双模指数二次型算符的连续变量纠缠态的量子涨落特性

利用线性量子变换理论（LQTT）,导出在Fock空间中连续变量两体纠缠态的量子涨落计算的一般公式,并讨论此纠缠态的压缩特性。通过线性拟合的方法,得到当涨落度和纠缠熵分别出现极值时,态参数之间关系。结果显示当达到较大纠缠时,该态的压缩程度也较大,除此以外还得到了涨落度随参数和纠缠熵的变化关系。同时举例说明此公式在计算双模压缩真空态和单边双模压缩真空态的量子涨落中的应用。     

Entanglement generated in a nanomechanical oscillator system

We consider a Fabry–Perot cavity with one fixed mirror and a movable perfectly reflecting mirror. Applying a linearised fluctuation analysis, we derive the quantum fluctuations and correlation matrix between the cavity and nanomechanical oscillator. We investigate the continuous-variable (CV) entanglement and squeezing between the cavity and nanomechanical oscillator. It is found that high intensity of entanglement and squeezing between the cavity and nanomechanical oscillator can be achieved.     

连续变量相干态量子神经网络模型的构建

为了将功能强大的神经网络应用到连续变量量子信息处理中,需要建立连续变量的量子神经网络(QNN)模型.以相干态量子逻辑门为基元,基于QNN原理构建了由输入层、隐藏层和输出层组成的量子线路,实现了连续变量相干态量子神经网络(CSQNN)功能.模型通过多控CNOT门实现量子态操作,利用相位旋转门完成网络参数的学习训练.仿真结果表明在CSQNN辅助下,阻尼系数为0.5的振幅阻尼信道的量子隐形传态保真度显著提高,趋近1,说明提出的CSQNN模型能有效处理连续变量量子信息.     

中间纠缠源离散调制CVQKD性能分析

连续变量量子密钥分发协议虽然具备更高的安全码 率等优势,但是其安全传输距离却一直表现不佳,而离散调制连续变量量子密钥分发协议已 被证明在低信噪比下能够获得比高斯调制更好的性能。基于 此,本文详细分析了光源非可信时,离散调制二态、四态和八态协议的性能,推导了安全码 率表达式。数 值仿真结果表明,当光源处于中间时,离散调制相干态零差检测正向协调性能优于其它协议 ,八态协议有更长的传输距离。     

基于后选择的连续变量量子密钥分发协议

连续变量量子密钥分发（CVQKD）是利用连续变化的物理量承载密钥的量子密钥分发协议,与电力系统普遍采用的离散变量量子密钥分发协议相比,其具有设备简单、探测效率高、兼容性好等优点,成为量子密钥分发的研究热点。然而,量子态在量子信道中的传输衰减严重限制CVQKD传输距离。提出了一种基于后选择方法的CVQKD协议,且不需要额外的单光子源。研究结果表明,该后选择方法中测量值越大的物理量被保留下的概率越高。该方法可以简化并降低连续量子密钥分发协议实现的成本,为探索出电力网络的量子保密通信方案提供研究思路。